Identifying and Managing Sycamore Blight on Sycamore Trees

Identifying and Managing Sycamore Blight on Sycamore Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Do you want the good news of the bad news first? The bad news is that many of our area sycamores are infected with sycamore blight this spring.  The good news is that sycamore blight seldom kills a tree.  Well, it's good news for those of you who like sycamore trees.  Most of you know that sycamores are not my favorite type of tree.  One reason that sycamores don't hold my esteem is that they get sycamore anthracnose .

Sycamore anthracnose, also know as sycamore "blight", is a fungus disease which commonly attacks the leaves and twigs of sycamore trees.  The cool, wet weather this spring has been ideal for the development of this disease.  The fungus survives the winter in cankers (which look like small wounds) on the branch twigs and also on fallen leaves and twigs.  During cool (55 degrees Fahrenheit), wet spring weather, the spores of the fungus develop in these cankers.  The spores are blown and splashed by the rain onto newly expanding buds, shoots, and leaves. The spores germinate and the fungus infects and kills plant tissue.

The first symptom of sycamore blight is usually sudden browning and death of single leaves or clusters of leaves as they're expanding in the spring. It’s easily mistaken for frost or wind injury.

A quick look around the area, and you’ll easily find a large number of sycamore trees that are quite sparse and appear to be leafing out very slowly.  Many of these are affected by “blight.”  As our weather turns warmer (hopefully), the trees will form new leaves but the foliage will not be as dense as in other years.

If our cool and wet weather persists, later leaf infections may also occur.  Symptoms of these later infections appear as brown dead spots which start at the base of the leaf or at avein on the leaf.  The brown spots then follow the veins outward.

Control of anthracnose on susceptible trees is difficult, mainly because of the large size ofmost sycamores.  Recommended cultural control consists pruning off and destroying infected twigs and dead branches and also raking up and disposing of all the fallen leaves and dead twigs.  Both of these actions are designed to remove the organism that lives through the winter and produces spores the next spring.

Spraying with a fungicide to protect expanding buds and leaves from the fungus can be done in the spring as the buds begin to swell andjust start to break open.  This is most practical where trees are young and small enough for you to be able to achieve good coverage when spraying.  Adequate coverage is difficult to achieve on large trees, even for competent applicators with good equipment.  Recommended fungicides are applied at bud‑break and then again at ten to fourteen day intervals during periods of wet weather. Remember that good coverage is essential for effective control.

I should note that sycamore and plane trees vary in their susceptibility to the disease.  Oriental plane trees are resistant while native sycamores are not.  There are some cultivated varieties of Oriental hybrids that are known to be resistant to the disease.  These varieties are "Bloodgood," "Columbia," and "Liberty."   If you must plant a sycamore, plant one of these resistant varieties.

Locust Borer Attacks Black Locust Trees

Locust Borer Attacks Black Locust Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

The locust borer (Megacyllene robiniae) only attacks black locust trees.  It’s a native insect and was first found in the eastern part of the United States in natural stands of black locust trees.  The locust borer caused problems in colonial times by rendering the durable black locust wood unsuitable for use as fenceposts.  As settlers moved west in the country, they brought black locust trees... and the borer with them.  The borer is now found throughout North America.

The adult locust borer is one of the “long-horned beetles” with antennae almost as long as its body.  This 3/4 inch black, slender, elongated beetle is sometimes mistaken for a wasp because of the distinctive bright yellow markings on its back.  Most characteristic is the “W” shaped band across the wings.  The legs are reddish.

As an adult beetle, this pest feeds on goldenrod and other flowers in late summer and early fall.  After feasting on flowers and mating, the female adult beetles lay eggs singly or in small groups in bark crevices, cracks, callus tissue around wounds, and other hiding places on the bark of black locust trees.  Interestingly, this egg laying activity usually takes place from early afternoon to late evening.

In about a week, the eggs hatch into tiny larvae which bore directly into the bark until they reach living tissue.  They spend the winter in the inner bark where they make a small hibernation burrow about one inch in length.  In the spring, they start feeding on the tree in earnest, boring upward and inward towards the center of the trunk.  At some point they make a sharp turn and descend about 3 inches down the trunk within the heartwood.  

They’re apparently good housekeepers, pushing frass and sawdust out of their entrance holes and other openings made for clearing out clogged tunnels.  In the spring, visible clues to their presence are moist areas on the bark, which is caused by sap coming from these opening.  The frass and sawdust materials pushed out of the tunnels and collecting beneath the trees is also a good clue.  They continue boring until the tunnels are three to four inches long and about 1/4 inch in diameter.  The tunnel is oval-shaped to accommodate their round head and the way it eats the wood.  It’s such a good eater, you can actually hear it feeding as it chomps away on the wood.

In mid-summer, the larvae, which have grown to approximately one inch in length, are ready to pupate... the stage where they change from a larva into an adult.  They emerge about a month later as adult beetles.  They exit through the openings they made as larvae.  There is one generation per year.

This past week I have been receiving samples and calls from numerous tree owners and cities in the region who are concerned about the damage from the borer that they’re finding in their black locust trees.  The city of Kahlotus has a great number of infested trees and the city of Richland is faced with the predicament of having 600 to 800 black locusts within their entire park system, with 60 or more in Howard Amon Park alone.  A number of these are badly infested and will probably need to be removed for safety reasons.

What type of actual damage does the borer do?  The beetles primarily attack the trunks and branches of black locust (Robinia psuedoacacia) trees, which are 1½ inches in diameter up to seven to eight inches in diameter, occasionally attacking larger wood.  It usually waits to attack trees until they’re four years of age or older.  Heavy attacks by the locust borer will weaken trees and retard growth.  Severe infestations or repeated attacks can leave wood virtually “honeycombed” and prone to limb breakage during windstorms.  During our last windstorm, a number of badly infested trees lost limbs and branches.

The borer tends to attack stressed trees more heavily.  The first line of defense against this pest is to keep the trees in as good health as possible with adequate watering and fertilization practices.  Usually older trees are not attacked, but when there is a high population of borers or the trees are stressed, the tops of older trees become infested too. 

While the locust borer doesn’t generally kill trees, trees can be killed when the population becomes epidemic in proportion.  Drought weakened trees are especially susceptible to attack.  Soil compaction also contributes to borer attack.  Even pruning creates favorable sites for infestation, since the adult females like to lay their eggs in callus tissue on the edge of wounds.

When the borer is already in the wood there isn’t much one can do in the way of “control” other than pruning out badly infested wood.  Chemicals applied to the bark will not penetrate and kill the larvae.  Systemics applied to the roots for uptake into the plants also don’t get into heartwood and older sapwood tissues where the larva does most of its feeding. 

Any chemical insecticides used for control are applications made to trunks and main branches to prevent reinfestation by young borers in the fall.  Appropriate applications of pesticides labeled for borer control are made in late summer or early fall.  Sprays are targeted at the bark of the trunk and larger branches (greater than one inch in diameter).  The spray applications should thoroughly wet the bark surface.  Special attention should be given to wounds and callus growth where the borers like to lay their eggs.

Heavily infested trees with dying tops serve as “brood” trees for the borer.  It would be advantageous to remove these trees from an area where other, healthier black locusts are growing.  However, the trees should be removed and destroyed during the dormant season when they contain the larvae.  Limbs and branches should also be removed if an attack leaves their wood structurally weak.  These should be removed as soon as the hazard is detected.  When replacing these trees, a community should consider planting a mix of species.  Pure stands or large groups of any one species invites devastation by an insect population or an attack by disease, like the locust borer or Dutch elm disease. 

One of the law’s of nature is “the survival of the fittest.”  This certainly applies to black locust trees.  Trees that are healthy and not stressed will survive; weakened trees will probably end up being dinner for the locust borer and candidates for the chainsaw.  

Fruit Trees Can be a Nightmare for Tri-Cities Gardeners

Fruit Trees Can be a Nightmare for Tri-Cities Gardeners

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

It=s a nice dream.... being able to grow fruit right in your own backyard.  However, this dream often turns into a nightmare for many home gardeners who are not aware of how much work it can take to grow acceptable quality worm-free fruit.  It requires regular sprays of insecticides to keep apple and cherry fruit free of worms.  Even if you tire of spraying and are willing to sacrifice your fruit to the Aworms@, residents of Benton and Franklin counties are required by law to control the wormy pests on apples, crab apple, hawthorn, and cherries.   The obstacles to growing backyard fruit trees often leads to many questions from would-be backyard orchardists when they discover that their dreams aren=t easily realized.  Here are some of their frequently asked questions... and answers.

Why do Benton and Franklin counties require me to spray my apple and cherry trees?  Backyard fruit trees, where codling moth and cherry fruit fly are not controlled, serve as a source of infestation for commercial orchards.  Infestations of codling moth and cherry fruit fly in nearby backyard trees mean a grower will have to use more insecticides or additional pest management strategies to control these pests in his orchard.  This leads to increased costs and an increase in the amount of pesticides used.  The infestation may also lead to infested fruit within his crop, which could mean the grower will get less money for his crop or it may even mean he can=t sell it at all.  Because commercial tree fruit production is a significant part of our local agricultural economy, it=s important to keep backyard fruit trees from becoming a liability to commercial growers.

How difficult is it to control these pests? Both codling moth and cherry fruit fly require regular sprays, generally every 7 to 10 days, during the growing season to keep the fruit Aworm free@.

Spraying trees is time consuming ... you have to mix the sprays, apply them, and clean up afterwards including laundering your clothing.  You also need the right equipment for spraying.  If the trees are large, you=ll need more than a hose-end or garden sprayer to reach the tops of large fruit trees.  It=s unsafe to spray fruit trees using a ladder.  You also should wear protective goggles, long sleeves, long trousers, a hat, and shoes when applying pesticides to your trees. These items must be laundered separately from other laundry right after spraying.

The weather can definitely make it difficult to apply the regular sprays needed to keep pests in check.  You should not spray when the temperature is expected to go below 40 degrees when applying dormant oils and you should not spray when the daytime temperature is above 85 degrees when applying sulfur or petroleum-based sprays. Wind can lead to the spray drifting off target, so you should never spray when there=s any noticeable wind.

If I apply a dormant spray, won=t that take care of the wormy pests?  No.  The dormant fruit tree sprays that are applied in the late winter just as buds start to swell are aimed at controlling diseases, not insects.  Dormant oils which should be applied just before the buds open in the spring, only help control certain insects that overwinter on the bark of the tree, such as aphids, scale, and mites.  The dormant oils have no affect on codling moth or cherry fruit flies.

I don=t like using so much pesticide.  Is there any organic way to control these pests?  Some organic sprays are available for codling moth and cherry fruit fly control, but most don=t provide adequate control to keep the home orchard worm-free and most would also require more frequent application.  Codling moth can be controlled without sprays, if you are willing to thin and bag all the apples on a tree using special paper bags. 

I=ve heard about the use of pheromones (insect hormones ) to control codling moth in apple orchards.  Wouldn’t that also work for a backyard orchardist like me?  The lures impregnated with insect sex pheromones are useful tools in codling moth management in large orchards.  The lures are placed around the perimeter of an orchard to confuse male moths looking for a mate.  Unfortunately, the lures have proven ineffective when dealing with small orchards or backyard fruit trees because mated females can come from nearby sources to lay fertile eggs on the apples.  Infested trees close to large apple orchards using lures for codling moth management increase the amount of spraying needed to keep the codling moth out of those orchards.

What about the insect traps advertised in garden catalogs?  Won=t they work in controlling the adult codling moth and cherry fruit flies?  The catalogs may be misleading you.  Codling moth traps are good tools to use to monitor the presence of these pests, but are not effective in eliminating damage because they attract only the male moths looking for a mate.  Again, fertile females can come in from nearby sources to lay eggs.. The yellow color and an ammonium carbonate bate on cherry fruit fly traps are what attract both male and female adult flies.  However, the traps are not considered adequate for good cherry fruit fly control.

Is diazinon still available to home gardeners to use on apples and cherries?  What pesticide can I use to control codling moth and cherry fruit fly?  There is still a number of home garden diazinon products commercially available that can be used on backyard cherry trees but only a few products are labeled for use on apples.  However, these products may not be readily available at your local garden store.   If you find a home garden product containing diazinon, be sure the label says it can be used on the type of fruit tree you have.  It is illegal to use the product on cherries or apples if they aren't listed on the label.

You may want to look for a home garden insecticide product containing a combination of malathion and methoxychlor for use on apples.  There are quite a few of these labeled as Afruit tree spray@ or Ahome orchard spray@ and most also contain a fungicide, captan, for disease control. 

Why shouldn’t I grow hawthorns and crab apple?  Their fruit also becomes infested with codling moth and can pose the same threat as infested apple trees do to commercial orchardists.  If you have a hawthorn or crab apple in your yard and it=s infested with codling moth, you must spray it regularly.  

How about ornamental flowering cherries?  Are they a problem for commercial growers?  Your ornamental Japanese flowering cherries don=t produce fruit and shouldn’t pose a threat to commercial cherry growers.  However, sometimes the rootstock from below the graft of a flowering cherry starts to grow.  It will usually be a cherry that produces fruit.  These shoots from the understock should be removed when they appear.  If the understock is the only part of the tree that=s still alive, then the entire tree should be replaced. 

Since apples and pears require so much spraying to keep them worm free, are there any other types of fruit trees I can grow without a lot of spraying?   There are no common wormy pests of apricots, peaches, nectarines, and plums that require regular spraying of the trees.  Your best bet is to grow plums, they don't require regular spraying and have a more reliable crop than peaches or apricots.

Verticillium Wilt, A Disease That Attacks Trees From Inside Out

Verticillium Wilt, A Disease That Attacks Trees From Inside Out

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

It’s a disease that becoming more of a problem in our region.  Its name is verticillium wilt.  Verticillium wilt is a fungus disease that attacks over 300 woody and herbaceous host plants.  While it can be a problem in the vegetable and flower garden, its attack of woody plants is what creates the most havoc for home gardeners. 

Imagine a lovely, healthy maple tree in your front yard... growing well with the proper watering, fertilization, and good care that you’ve provided over the years.  One summer half the tree suddenly wilts and dies.  This scenario could happen if your tree is attacked by verticillium wilt.

There are lots of tree species it can attack, but there are some that it commonly attacks in our region.  These are maple, ash, catalpa, redbud, smoke tree, sumac, and Russian olive... with maple being the tree most often attacked.

Verticillium wilt fungus is a sneaky disease, entering a plant through the roots in the soil.  Infections are not obvious like some other diseases, such as powdery mildew or sycamore blight.  Symptoms can be acute... with leaf curling and drying, abnormal red and yellow coloring of the leaves, partial defoliation, wilting and dieback of branches.  This wilting and dieback will typically develop on one main branch, a sector of the crown, or an entire side of the tree.  Chronic symptoms are stunted growth, yellowish leaves, crispy brown edges on the leaves, slow and stunted growth, heavy seed crops, and branch dieback. 

Trees with verticillium wilt may limp along for years, exhibiting symptoms some years and other years not showing up at all.  However, the disease can suddenly attack a completely healthy tree causing it to wilt and die in a short period of time.

The first outward symptoms of verticillium wilt are leaf scorch, abnormal coloring, and dieback of branches.  However, there are many things that cause the same symptoms.  Girdling and encircling roots, root and crown rot, drought stress, compacted soil, trunk injury, and improper planting can all cause similar symptoms.

When verticillium wilt is suspected, a pocketknife should be used to make a slanted cut on an affected branch.  When verticillium wilt is present the cut may reveal streaking or discoloration of vascular tissue (transport) tissues in the wood.  In some species, like maple, this streaking is olive-green, but it varies from tan or brown to green or even black in some species. 

What causes this streaking?  The verticillium fungus once inside a tree, invades the xylem which is the water conducting tissue in roots, trunks, and branches.  The fungus produces toxins that can kill cells, even cells not close to the infected tissues.  The disease spreads in the plant by spores.  New fungal spores move upward with water in the vascular tissue.  The spores then lodge in healthy vascular tissue and new infections begin.  Dead and discolored tissues develop at the sites of these infections, first appearing slightly discolored and then developing the characteristic color for the species.  It’s this discoloration that causes the diagnostic streaking in vascular tissue.

The infected tree reacts to this fungal invasion by trying to block its spread.  It does this by producing gums and tyloses (chemical substances) in the vascular tissue to block fungal movement.  However, these gums and tyloses also impede the flow of water.  This results in the external symptoms of verticillium wilt that can be confused with other causes that also deter a tree’s uptake of water.

When looking for streaking in a recently wilted branch, the first place to look for streaking is directly under the bark.  If no streaking if found there, a deeper into the sapwood may reveal streaking.  However, streaking may not be evident even if the plant is infected with verticillium wilt.  It typically is not present in recently infected sapwood and is usually not found in twigs of one inch in diameter or smaller.  Streaking will most likely be found near the base of the tree, since the initial infection route is usually through the roots.  As you move up the tree, you’re less likely to find streaking.  To make diagnosis even more difficult, there is no detectable streaking of vascular tissues on certain species, like ash.

Before we talk about management of verticillium wilt, let’s talk a just a little more about it’s life cycle and how it enters a tree.  The wilt’s microsclerotia, which are tiny black resting structures, can be found in many soils.  They spread by wind or water.  They can also be introduced into “clean” soil from contaminated seed and plants or from contaminated soil on root balls, hand tools, or machinery.  They can exist in the soil for many years, up to 15 years, without contact with a host plant.  Lying in wait, the microsclerotia will germinate and infect a new plant when they come in contact with the roots of a susceptible host.  They invade the roots through a wound or by direct penetration.  Once inside the host, the fungus gets into the vascular tissue and spreads throughout the plant by spores. 

So how do we control the disease?  Plain and simply, you can’t control verticillium wilt once a tree is infected.  No fungicides have been found to be effective against the fungus in trees.  Injections of fungicides into a tree have been tried, but the results have been inconclusive.  You may not be able to control verticillium wilt, but you can try to manage it.  Just because a tree is infected, doesn’t mean it will die.  It may recover and be able to live with the disease... with careful management.

Trees should receive plenty of water to promote growth and avoid stress.  Infection is less severe when trees are not drought stressed.  A good deep soaking once a week during hot summer weather will help.  Fertilization with ammonium sulfate, when symptoms are first noticed, is recommended by many “verticillium wilt” experts.  Research in Michigan indicates that you should avoid applications of nitrate fertilizers because they ineffective in management of the disease.  While fertilization is part of the management program, you should avoid excessive fertilization, which apparently can increase problems with the disease.

You will want to promptly remove branches killed by the disease but you shouldn’t remove them until you give the water and fertilizer a chance revive recently wilted branches.  If they don’t come back in response to the extra care, remove the branches, cutting well below any of the streaking or discoloration and back to a main branch or limb.  Be sure to make proper pruning cuts and don’t leave stub cuts.  In between cuts, disinfect your pruning sheers with 70 per cent rubbing alcohol or a 10 per cent bleach solution.  Wood from infected branches should be removed and destroyed.  Chipping the wood and using it for mulch can spread the disease to other areas.

If a tree dies and needs to be replaced, keep in mind that the microsclerotia can remain in the soil for over 15 years.  When replanting, select a species of tree that is resistant to the disease.  Trees reported to be immune or resistant to verticillium wilt include beech, birch, ginkgo, honeylocust, sycamore, hophornbeam, sweetgum, pear, mulberry, apple, hawthorn, willow, white oak, bur oak, and sycamore.  Dogwood and linden appear to be susceptible to some strains of verticillium and resistant to others.  Fir, spruce, pine, juniper, and arborvitae are also resistant.

Sycamore Problems

Sycamore Problems

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

Lace Bugs

Just this past week, several people have brought me samples of ailing sycamore trees.  On each of these samples there were two problems worth mentioning.  One problem was an insect, the sycamore lacebug.  It’s a tiny bug with lace-like wings.  It sucks sap from leaves creating a speckled appearance. The lace bugs can be found on the undersides of leaves along with small black specks of their excrement.   When feeding is severe, the leaves take on a brownish or dry look. 

The lace bug has not become a serious annual problem on sycamores, but it does show up from time to time.  The amount damage it causes is typically insignificant and tends to only become extensive in late summer or early fall.  With damage occurring so late in the season, control is not needed.

Herbicide Injury

The other problem evident on these samples was more noteworthy.  The leaves were somewhat malformed and cupped downward with an excess of the leaves’ natural hairy fuzz.  This is a sure sign of herbicide injury.  It was very likely caused by applications of “weed and feed” products to the lawn.  Dicamba or 2,4D, commonly found in “weed & feed” products, were probably the herbicides at fault.  Sycamores are particularly sensitive to damage from these two herbicides.

The downward cupping of the leaves is not critical. After all, the tree will soon be losing these leaves in preparation for winter.  The real damage from these lawn herbicides happens to the trunk of the tree.  Both herbicides can lead to damage of bark tissues and the emergence of bark eruptions on the main trunk, usually more extensively on the lower portions of the trunk.  The bark loses its beautiful mosaic pattern and smooth appearance.  It becomes rough and fissured.  Immediately beneath the eruptions, the bark tissue is pink and spongy.  Beneath the eruptions, the inner wood becomes dark brown.  This damage may later attract a borer, the American plum borer, which then causes even greater damage to the bark and trunk tissues.

Dicamba and 2,4 D can cause damage to sycamores even when applied at the correct rate, but greater damage occurs if they’re over-applied.  Over-application often occurs when home gardeners don’t calibrate their drop-spreader or sprayer before applying a “weed and feed”.  As a rule, 2,4 D and dicamba should not be applied in a general application to the lawn over the root zone of sycamores.  Spot treating weeds is safer for the sycamores and more economical.

Leaf Scorch

Yet another problem being noted by some sycamore owners is leaf scorch.  This shows up as bright yellow to brown leaves scattered throughout the crown and accompanied by substantial leaf loss.  The leaves most severely affected are the oldest... especially the inside leaves.  The most likely cause of this problem is heat and drought.  It’s been a hot summer.  Sycamores are big trees and if they don’t get enough water they let you know.  Lack of deep watering, girdling roots, and compacted soils can all be factors in a sycamore becoming drought stressed.

New Ways to Control Worm Pests in Fruit Trees

New Ways to Control Worm Pests in Fruit Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

If you own an apple, crabapple, pear or fruiting cherry tree, you may be wondering what to do about controlling worms in the fruit.  With apple, pear, and crabapple, regular sprays are needed to prevent the codling moth larvae from boring into and destroying the fruit.  These sprays start not long after full bloom and continue until close to harvest.  With cherries, regular sprays are needed to control the cherry fruit fly to prevent the cherry fruit fly from laying its eggs under the skin of developing cherries.  The eggs develop into those nasty Aworms@ or maggots found inside a cherry, destroying its palatability and storage life. The sprays for control usually start in mid-May and continue until close to harvest.

Because residents of Benton and Franklin counties live in a region with an important commercial tree fruit industry, they=re required by county law to control these wormy pests in any fruiting apple, crabapple, pear, or cherry trees on their property.   Infested backyard trees are a source of contamination for any nearby commercial orchard.  This can lead to commercial orchardists having all their fruit rejected by a packing house and the need to apply pesticides more frequently to keep their fruit worm free. 

Limited Pesticides Available to Prevent Wormy Fruit

Even responsible home gardeners are having an increasingly hard time controlling these wormy fruit pests.  The reason is that there aren’t many effective chemicals still available to home gardeners for use on fruit trees to control these pests.  In past years, weekly sprays of diazinon would control them, but diazinon will not be available after this year.  The limited diazinon products still available have very restrictive labels, limiting the number of times they can be applied to fruit trees during the growing season.

There are only two home garden products labeled for use in Washington containing combinations methoxychlor and malathion, two insecticides that can be used on apples and cherries for effective control of codling moth and cherry fruit fly. They are Ortho=s Home Orchard spray and True Value=s Greenthumb Liquid Fruit Tree Spray.  These may be difficult to find, but are available.  Methoxychlor-malathion mixes will provide adequate control when applied every 7 to 10 days.  There are also several products that contain malathion without methoxychlor and should also provide adequate control.

Clay Deters Codling Moth

One non-chemical material that can be used by home gardeners is a product called Surround.  Surround consists of highly refined kaolin clay.  Mixed with water, it=s sprayed onto trees.  The white clay particles coat the leaves and the fruit.  Researchers have found that rather than killing pests, this material acts as a repellent or deterrent to insects.  Insects do not like the coated surfaces and fail to deposit many, if any, eggs on the treated surfaces.  With some insects, the kaolin coating may simply hide the host plant from an insect=s chemical receptors, preventing the pest from finding the plant.

Unfortunately, while Surround has been extremely effective in repelling some pests, it=s not completely effective against codling moth, only reducing codling moth damage between 30 and 90 per cent from untreated controls.  Even if it was completely effective, home gardeners might not find treated trees aesthetically acceptable since the treated trees are coated with a chalky white coating, giving them a ghostly appearance.  In addition, the harvested fruit requires thorough washing to remove the kaolin coating.

One Product Not Available to Home Gardeners

University researchers and chemical companies are searching hard for effective materials to help control pests with less chemicals and less impact on the environment and beneficial insects.  One new product that has been developed is ALast Call@.  This is a paste that=s applied from a custom dispenser as droplets about the size of a small pea onto the trunks and main branches of each apple tree in an orchard.

ALast Call@ contains permethrin (an insecticide), a UV protectant to keep the material from breaking down too quickly, and an insect pheromone (sex attractant). The material is designed to attract the male moths to the droplet and then kill them.  After contacting the droplet and finding out it=s not a sought-after female moth, a male moth becomes paralyzed and quickly dies. ALast Call@ must be applied before the male moths have a chance to mate with the females.  That=s because the females aren’t attracted to the pheromone droplets.  Once they=re fertilized by the male moth, they start laying eggs... leading to fruit damage. Once the females are laying fertile eggs, it doesn=t matter if the males are dead or alive.

While ALast Call@ has provided positive results in commercial orchards, in a Utah State University research study it proved ineffective in controlling codling moth in home orchard sites.  The reason for this failure was probably due to fertilized females from outside sources (such as nearby unsprayed, infested neighborhood trees) depositing eggs on the treated trees.  Remember that ALast Call@ doesn’t harm the females, just the males.  ALast Call@ may become available to home gardeners in Washington as early as this year, but some regular pesticide applications will probably still be necessary to adequately control codling moth when it=s being used.

One New Produce Provides Some Control

Spinosad is another new insecticide product.  It=s made from two spinosyns.  Spinosyns are naturally derived chemicals with insecticidal activity.  The spinosyns were supposedly discovered in 1982 by a scientist who was vacationing in the Caribbean.   The scientist collected soil from an abandoned rum distillery and discovered a new bacteria, named Saccharopolyspora spinosa, in the soil.  (That sounds like an odd vacation even for a scientist.)

This newly discovered bacteria produced metabolites from the fermentation process that were found to have insecticidal properties.   New insecticides, spinosyns, were derived from these metabolites.  The spinosyns act on an insect=s nervous system, causing hyperactivity, paralysis, and death in a relatively short amount of time.  It sounds a bit gruesome, but they=re very effective on some insects and they have extremely low toxicity to humans and animals.  Spinosad, formulated in 1988,  kills a variety of pests, including codling moth, but doesn=t harm many beneficial insects.  Spinosad provides moderately good control of codling moth on apples, but does not provide adequate protection when infestations are heavy.

How about Traps?

If you open a garden supply catalog you may see insect traps recommended for control of codling moth or cherry fruit fly.  These traps really only help tell you when these pests have emerged and help you in timing any control spray applications.  Traps for codling moth only attract the male moths, leaving fertile females to lay their eggs without impunity.  Yellow sticky traps catch both male and female cherry fruit flies, but they only trap some of the flies.  The don=t catch the majority of flies and are not effective controls. 

The Bad News

The bad news is that there are fewer and fewer tools available to home gardeners for controlling codling moth satisfactorily.  While there are some newer, less toxic materials and methods available now and on the horizon, they currently don=t promise to totally prevent damage from infestations.  If planting a fruiting apple, crabapple, pear, or cherry tree, one might even want to ask if it=s worth the trouble... considering the difficulty, time and expense involved in controlling these pests.

Avoid Spreading Disease by Pruning

Avoid Spreading Disease by Pruning

Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist

What’s your favorite type of pruning tool... a pair of ratchet hand pruners, a lightweight pair of loppers, or a handy folding pruning saw?  Tools like these are standard equipment for gardeners who have a lot of trees and shrubs in their landscape.  They’re needed to prune off ill-placed branches, remove older wood, and eliminate any dead or diseased portions of a plant.  Removal of these infected tissues is very important in preventing the spread of disease.  However, many of us home gardeners may actually be spreading disease if we’re not disinfecting our pruning tools between cuts.

How can pruning tools spread disease?  According to WSU Plant Pathologist, Dr. Warren Copes, if you cut through a section of stem where a pathogen, such as a virus, bacteria, or fungus is present, then the parts of the pathogen may adhere to your pruning tool. When certain diseases are suspected, it’s a good idea to disinfect your pruning tools after every cut.

Copes also points out that not every dead branch is the result of an infection by a disease.  There are also cultural and environmental problems that can lead to dieback.  Let’s look at some common diseases that cause problems in our area and the “protocol” suggested for disease management through pruning and disinfecting the tools we use.

When we have cool, wet springs, a common problem in this area is sycamore anthracnose, also known as sycamore “blight.” True to its name it attacks sycamore trees.  This fungus disease causes cankers or lesions, which eventually girdle a stem and lead to the death of tissues beyond the canker. Over time, repeated infections create sycamores with unsightly crowns.

Where practical, it’s recommended to prune out the cankers caused by the anthracnose fungus.  This improves a tree’s appearance and more importantly removes a source of future infections.  Cuts should be made four inches below any discolored wood.  The disease is spread primarily by wind and rain, not by pruning equipment.  With this disease, you don’t need to disinfect pruning tools after cutting off infected tissue.

One fungus disease that we’ve seen quite a bit of this year is verticillium wilt fungus.  Unlike sycamore anthracnose, verticillium wilt is distributed within a plant at considerable distances from the area of obvious dieback.  It usually enters the plant by way of the root system and moves through the vascular system to plant tissues.  Dieback of branches and limbs is caused by impairment of the root system and the plugging of the vascular system... the system that transports water and nutrients within the tree.  In our region, verticillium wilt is a common problem on maple, ash, sumac, redbud, catalpa, Russian olive, and smoketree. However, there are many other types of trees, shrubs, and garden plants susceptible to verticillium wilt.

While the verticillium wilt fungus can travel throughout a tree, it’s usually not evenly distributed in the plant.  Copes points out, “Since the pathogen isn’t evenly distributed, it’s difficult to identify where the pathogen would be located and also why the fungus is not always spread on pruning tools.”  Dead portions of trees infected with verticillium should be pruned out, but we must keep in mind that this doesn’t remove the pathogen which is located in the roots.  Pruning tools used on trees that have been diagnosed with verticillium wilt or are suspected to have it, should be disinfected between trees and when you are done pruning.

Some “blights” or diseases are caused by a bacterium rather than a fungus.  The most common one that can cause problems in local landscapes is fireblight,  Erwinia amylovora.  Fireblight attacks many members of the rose family including apple, flowering crabapple, pear, pyracantha, hawthorn, cotoneaster, quince, and mountain ash.

Symptoms of a fireblight infection usually start in the spring with infected flowers appearing water soaked.  The flowers may turn brown to black and fail to fall from the tree or shrub.  The bacteria moves down the infected blossom into the twigs, resulting in the sudden death of other flowers and fruits on the same twig.  Often, the twigs will develop a hooked tip or"shepherd’s crook."  Twigs and leaves look almost black, as if scorched by fire.  As the bacteria moves down a twig into a branch, the tissues darken and die. If the outer bark is cut or peeled away, the inner tissues will appear red and water‑soaked.

Fireblight infections commonly occur in the spring when bacterial strands from dead infected tissues are splashed to flowers by rainfall or irrigation water.  The bacteria may also be spread to the flowers by insects that have visited infected plants.  Fireblight often enters a plant through natural openings in the floral parts.

Infection is favored by wet weather and temperatures between 65 and 86 degrees Fahrenheit.  Because of the relatively low rainfall conditions in this region, fireblight is not often a problem in home landscapes.  However, in some years the spring moisture and temperature conditions are just right.  This past spring’s weather provided perfect conditions for fireblight infections in a number of home landscapes.

Once an infection is noted in a plant, it’s important to prune it out immediately.  Pruning cuts should be made at least 12 inches below any discolored wood.  This is because discoloration is a chemical response by the infected plant.  It takes a while before the discoloration forms in infected wood. 

This rule of pruning at least 12 inches below discolored wood can cause a dilemma.  Copes notes that, “Sometimes, a blighted twig or spur may be less than 12 inches away from a larger limb and such removal would disfigure the tree.  In this case, there is no easy answer. Removing the scaffold limb may be necessary.”  If you don’t remove the limb, you should monitor the tree to see if the disease is still present.  While 12 inches is the rule, the disease doesn’t always follow the rules.  It may be present further down, especially if there is a length of time from the first appearance of symptoms and the removal of infected wood.

Pathologists have not been able to confirm that contaminated pruning tools actually spread fireblight from one plant to another.  However, the accepted practice when pruning off fireblight infected wood is to disinfect pruning tools after each cut.

Now we’ve talked about when you should disinfect your pruning tools, but just how should the tools be disinfected?  Plant professionals use a variety of materials to disinfect their pruning tools including commercial horticulture products and also other chemicals.  An article on disinfecting horticultural tools is available from University of Florida IFAS Extension at:  http://edis.ifas.ufl.edu/ep380t.

Be aware that some disinfecting chemicals are corrosive.  Make sure to wash the chemical off after the final disinfecting, allow the equipment to dry thoroughly, and then coat the metal parts with light oil or a silicone based spray.  If viruses are the suspected disease, clean your tools by washing them with detergent to physically remove the virus and inactivate virus that may remain on the blades.

Managing Mite Problems

Managing Mite Problems

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

It might be mites, it might not.  Spider mites are often blamed for plants turning brown evenwhen they=re nowhere to be found on a failing plant.  How can you tell if your tree, shrub or garden plant has mites? 

What are Mites?

Spider mites are not insects.  They=re tiny arachnids related to the other arachnids that we know and Alove@, includingspiders, ticks, and harvestmen (daddy longlegs).  Like their relatives, spider mites have eight legs and lack wings, antennae and compound eyes.  Members of the insect family typically have six legs, antennae, compound eyes and wings.

Spider mites are visible, but extremely small (1/60th of an inch in length or smaller) and almost microscopic. One way to tell if a plant has mites is to tap a branch or some leaves suspected of having mites over a piece of white paper.  Invariably, little dust specks will fall onto the paper.  If after a second or two the little specks start crawling, it=s a good bet that they=re mites.

The other way to detect a mite problem is to look for their damage and other signs of their presence.  Spider mites don=t have chewing or piercing-sucking mouthparts. To access plant sap they pierce and rupture leaf cells with needle-like stylets.  They then suck up sap that seeps out of the punctured cells. This type of damage leads to the death of individual cells, giving the leaf a finely stippled appearance. As the damage increases a leaf appears discolored, then it turns yellow to brown and dies.  Some types of mites even inject a toxin when they feed which can lead to leaf distortion.

Another sign of a mite infestation is webbing.  The webbing is very fine and, depending on the type of mite, is often found on the undersides of leaves.  It shouldn=t be confused with more visible webbing made by spiders or the cottony masses from cottonwood and poplar trees.  However, it=s important to note that not all spider mites produce webbing... so you can have a mite infestation without webbing.

Mite Life Cycle

Knowing the life cycle and habits of a pest enables us to better manage that pest when it becomes a problem.  Because the two-spotted mite is the most common spider mite that causes problems for trees, shrubs, garden flowers, and vegetables let=s take a look at its way of life. 

The two-spotted spider mite, thus named because of the two dark spots on the back of the adult mite, start out as an egg.  The egg hatches into a larva that has only six legs.  This larva molts into a nymph with eight legs. The nymph molts into a larger nymph and then becomes an adult.  Both the larva and the nymphs resemble the adult.  This entire process takes about five to 20 days depending on the weather.  When winter comes, many types of mites overwinter as eggs. However, the two-spotted mite overwinters as an adult in the soil or in bark crevices on trees and shrubs.  They become active as soon as plant growth begins in the spring.

Mite Build-Up

During hot weather, two-spotted mite populations can build up quite quickly causing plant damage.  A female two-spotted spider mite lives approximately 30 days and lays about 100 eggs. One reason that hot weather leads to spider mite explosions is because of the low humidity.  With low humidity the excess water they excrete evaporates more rapidly.  This allows them to feed more heavily, favoring reproduction.  Another factor is that many of the natural mite predators are stressed by the hot, dry conditions and aren=t able to multiply quickly enough to keep up with the burgeoning mite population.

Hot weather doesn’t=t favor all types of mites. One very notable exception is the spruce spider mite that feeds on conifers, especially spruce and juniper.  This mite is most active during cooler spring and fall weather and actually goes dormant (in an egg stage) during hot summer weather.

Natural Mite Control

Spider mites do have some natural enemies.  They=re Adinner@ for predatory insects, such as dark- colored lady beetles, lacewings, predatory thrips, minute pirate bugs, and big-eyed bugs.  There are also a number of predatory mites that feed on spider mites and keep their populations under control especially when the weather isn=t extremely hot and dry.  One reason for spider mite outbreaks when the weather is not hot is that these predatory mites are killed off when insecticides are applied to plants.  They=re particularly sensitive to carbaryl (Sevin), but may also be harmed by other insecticides.   To keep spider mites in check, avoid using pesticides that kill off predators.

Controlling Mite Infestations

One cultural technique that helps keep mite populations in check is periodically syringing mite-prone plants with a forceful spray of water.  This forceful spray not only knocks off and kills the spider mites, but also dislodges the webbing that collects dusts and deters the natural predators.  It=s also important to keep plants from becoming drought stressed in hot weather.  Plants under stress are more vulnerable to spider mite attack.

If cultural controls don=t work, then pesticide sprays may be needed if significant damage is showing up on your plants.  Since mites aren’t=t insects, most garden insecticides are not very effective.  There are specific miticide chemicals for mite control, but they=re not readily available to home gardeners.  Two options that are available are insecticidal soaps and horticultural oils.

Insecticidal soaps are only moderately effective against mites.  For best results good coverage to both the upper and lower leaf surfaces is essential.  (Remember most mites are on the bottom of the leaves.)  The soap is only effective on the mites that are contacted with the soap spray.  Eggs are not harmed, so repeat applications are usually needed within seven to ten days in hot weather. Additional retreatments may be needed. 

During the growing season horticultural oils may be applied at the summer rate... but be sure to check the label for any hot weather precautions.  Horticultural oils may also be used on dormant plants in the spring at a dormant application rate for controlling overwintering adult mites and mite eggs. 

Spider mite infestations are not as common as some gardeners think.  I sometimes see infestations of spider mites on willows, marigolds, roses, and impatiens.  Spruce spider mites are occasionally a problem on area junipers and spruce, especially dwarf Alberta spruce.  I very seldom see spider mites on arborvitae or other landscape and garden plants.  So if your plants start to turn brown, check for stippling, crawling specks of dust, and very fine webbing on the undersides of leaves.  If in doubt, take a sample to your local Master Gardener Plant Clinic

New Pesticide for Control of Shade Tree Insects

New Pesticide for Control of Shade Tree Insects

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

There continues to be concern about our dependency on chemicals for pest management in yards, gardens, and agricultural crops.  Chemicals that we have relied upon for years have recently come under scrutiny for one reason or another.  Many of these "old" chemicals have one or more objectionable characteristics, such as they're very hazardous to the applicator due to their extreme toxicity in a concentrated form, they don't break down very quickly in the environment, they pose a threat to groundwater due to their leachability, or they may lead to long term health effects like cancer.

It's been said that, "Necessity if the mother of invention."  This is true when it comes to pesticide chemistry.  With concerns about old pesticides and their chemistry, the pesticide industry has worked hard at formulating new and safer chemicals which will be more environmentally friendly and thereby more acceptable to consumers.  Of course, these new chemicals must also do a good job of controlling the pest... whether it's a weed, insect, or plant disease.

One fairly new chemical on the commercial market is an insecticide known by the trade name of Merit.  Its common chemical name is imidacloprid.  Merit has been quite popular for several years in areas where lawn grubs are a problem.  However, since lawn grubs are not usually a serious problem in this area, you've probably never heard of Merit.  Merit is also labeled for use on trees and shrubs. Local pest control operators have started applying Merit to area landscape trees with fairly good results.

Let's take a look at this new chemical.  Bayer Corporation, who manufactures Merit, indicates that it's a "broad-spectrum insecticide."  This means that it kills a variety of different insects.  The label lists numerous sucking insects and some chewing insects which can be controlled with Merit.  These include aphids, adelgids, elm leaf beetles, lacebugs, leafminers, leafhoppers, pine tip moth larvae, scale insects, and thrips.

Bayer also indicates that Merit is a systemic insecticide which means that it's taken up into the plant sap and moves to different parts of the plant.  Bayer indicates that it can be applied as a foliar spray to the leaves or applied to the soil for root uptake.  They point out that soil application is more efficient and effective for long-term insect control.  

Merit uses "new chemistry" and is very low in toxicity to humans, mammals, birds, and fish.  It's used at extremely low rates and there's no odor or phytotoxicity problems (damage to plants.)  Soil treatment also eliminates the chance of spray drift, reducing the potential exposure of humans and pets to this chemical.  Most beneficial insects are also safe with soil applied Merit.

Merit can be applied to the soil as either a drench or by injection.  Commercial applicators often opt for soil injection because it's the easiest to apply when they have the proper equipment.  Injections can be placed right at the base of the trunk; in a grid pattern below the tree's dripline; or in a circle at the dripline of the tree.  Bayer research indicates that all of these methods of placement are equally effective.  Many commercial pest control applicators choose the base treatment because it's most efficient.  Injections are placed a foot or less away from the base of the tree at a depth of six to twelve inches.  If the soil is dry, it's important to follow the application with adequate irrigation to thoroughly moisten the soil.  The soil in the application area should be kept moist for seven to ten days after treatment.  The number of the recommended injection sites increases with the size of the shrub or tree.

Now here's one of the interesting characteristics of Merit...  it will provide season long control if it's applied in late fall or early spring.  It takes about two to three months after application for it to become fully effective in the control of foliar pests on large trees.  It takes about a month after application on small trees and shrubs to become effective.  With this time lapse between application and full effectiveness, it's obvious that it must be applied prior to the time that the anticipated pests will be at their peak.  Foresight is much better than hindsight when using Merit. Fall application would logically be the best time to treat shade trees for aphid problems. 

Merit is now available to home gardeners so that they can treat their own trees and shrubs.  Merit is living up to it's manufacturer's promises... as long as it's applied early enough to become fully effective... and enough water is available to keep the soil moist for at least a week.  As Merit gains in popularity we'll probably not even miss some of those older chemicals that controlled the same pests, but were not as safe to use or as friendly to the environment.  Necessity made it happen.

Aphids Make Trees Sticky

Aphids Make Trees Sticky

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent

 “Why are the leaves of my trees shiny and sticky?  My trees are weeping and get everything underneath so sticky, what’s wrong with them?”  As summer progresses, we’re starting to see more insect pest problems bothering trees, shrubs, and other ornamental plants.  One major insect offender is aphids.  Aphids are often a perennial problem on some types of plants.  With trees and shrubs, like maples, ash trees, and roses, it’s a continual battle to keep aphids at reasonable levels.

Knowledge of your adversary can give you a tactical advantage in your yard and garden confrontations.  Aphids are soft-bodied insects which feed on plants by piercing leaves, stems, or twigs and then sucking out plant sap.  They often suck out more sap than they can use and secrete the excess as a sticky waste... called “honeydew.”  Honeydew is mostly sugar and water and isn’t harmful.  This sticky goo, or honeydew, may be eaten by other insects, or a black mold may grow on it.  This black mold, called sooty mold, is not harmful to the plants.

Along with the problem of “sticky trees,” aphid feeding can cause other problems.  Excessive feeding can lead to a loss of plant vigor and retard growth.  Aphids also secrete a saliva into plants while they feed.  In many plants this saliva causes distorted plant growth in the form of curled leaves, swollen nodes, and distorted growth.  Repeated severe annual infestations can lead to plant die-back.

Before trying to manage any insect population that has gone beyond tolerable levels, you need to understand the insect and it’s life cycle.  There are many different types of aphids with varying life cycles.  Entomologists say that there is probably at least one species of aphid that feeds on nearly every type of plant... trees, shrubs, flowers, vegetables, row crops, and weeds!  With so many different species of aphids it’s hard to know the exact life cycles of all of them, especially since aphids seem to have such a complex and strange life cycle.

Aphids can overwinter as eggs or mature adults.  In the spring, the eggs hatch into “Big Mommas” (actually, entomologists call them “stem mothers”) who produce live young without the “disadvantage” of mating.  These daughters also mate asexually, producing even more daughters.  You can see that without the need for mating that aphid populations can build up quite rapidly.  In fact, it has been estimated that one cabbage aphid “Momma” can be responsible for a family of 1,560,000,000,000,000,000,000,000,000 aphids by the end of the season... under ideal conditions. 

If you’re wondering where all these aphids might be hanging around, they’re probably not all still alive.  Aphids take about one week to mature and then most live for only about three weeks.  Many become the dinner for other insects.  If the colony becomes too crowded or the host plant is stressed, winged aphids are produced so they can move out on their own and seek new sources of food. In the fall, some aphid species produce both male and female aphids for the purpose of mating.  After mating the females lay eggs in protected locations, such as in buds or cracks in the tree bark, for overwintering.

Now we know the life cycle, but what about how aphids look?  Identifying the right pest is important.  As mentioned before, aphids are soft-bodied insects.  They come in a variety of colors including green, white, yellow, brown, black, gray, pink, purple, or red.  Some are even covered with a whitish “wooly” or cottony coating.  Aphids are usually found in large groups on plants, often on tender new foliage or the under sides of leaves.  Most aphids don’t move too fast... as you can’t budge them easily once they’ve found a good source of food.  They know a good thing when they taste it!

Now that we know more about how aphids live and grow, let’s talk about when and how to “control” them.  There are some fairly innocuous methods you can try... when and where they’re practical.

1. First look for signs of natural control.  Aphids have a number of natural enemies... ladybird beetles and their larvae, green lacewings, small parasitic wasps, syrphid fly larvae, predacious stink bugs, and assassin bugs.  If you’re able to find evidence that these natural enemies are present and working, don’t do anything unless the aphid population appears to be beyond their control.
2. Dislodge aphids with a fine but forceful spray of water from your hose. Be sure to move the spray back and forth as well as directing it towards the undersides of the leaves.  This will kill some aphids and many will not make it back to the plant.  Repeat this every several days.  This method of control can’t be used effectively on small or tender plants.
3. On some plants you can simply wipe aphids off plant stems or buds.  However, you may want to wear a pair of garden gloves to do this.  Snip off badly infested branch or stem tips.  Avoid fertilizing your plants with too much nitrogen.  Soft, lush growth encouraged by excess nitrogen is exactly the type of growth that aphids thrive upon.
4. Avoid aphid buildup early in the season on woody trees and shrubs by applying dormant oils to plants that have had problems with aphids in the past.  The dormant oil should be applied in early spring when temperatures are above freezing, but before the buds start to show green tissue.  Use according to label directions... of course.
5. If aphids are out of control and an insecticide is warranted, first consider the use of insecticidal soaps.  These are good materials to use because they protect a number of the “good” insects and they are very low in toxicity.  It’s important to get good coverage and to spray both the tops and bottoms of the leaves.  Repeat as needed.  Check product labels to avoid applying to plants sensitive to soaps. Don’t apply to stressed plants.
6. When aphid infestations are so severe that no other method of control is practical, a chemical insecticide may be needed to prevent further plant injury.  There are a number of pesticides labeled for control of aphids on plants.  However, some of these can only be used on ornamental plants because of their systemic action... meaning that they’re absorbed into the plant sap and move within the plant’s vascular system.  Systemics are particularly useful when aphids are protected by the leaves curled with their feeding damage.  Curled leaves protect aphids against contact insecticides.  Some materials are systemic sprays, such as Orthene, which is taken up into the plant sap of treated leaves.  Others, such as Merit or Di-Syston, are applied to the soil and absorbed with water by the roots.  

Root applied systemics are a practical way of treating a large shade tree with severe aphids populations.  They’re also less detrimental to the beneficial insects in the area.  Di-Syston and Merit (imidacloprid) are available to home gardeners.  Other soil applied systemics, such as Cygon, are available only to licenced commercial pest control operators.  Cygon can be used by home gardeners as a spray, but it’s illegal for them to use it as a soil applied drench on shade trees.  Keep in mind that most systemic insecticides are quite toxic to humans and animals.  Some plants may also be injured by the use of certain systemic insecticides.  Carefully read and follow all the label directions when using a systemic insecticide or any other pesticide product.

Aphids can be pesky, but a little knowledge about how they behave and how to safely manage their populations can lead to truce in your yard and garden.

Why Are All the Birches Dying?

Why Are All the Birches Dying?

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Even if you don’t own a birch tree, it would be hard to ignore the fact that so many birches in our area are dying.  There are various factors involved, but the causes involve stress, winter injury, and a devastating insect borer.

Birch trees are generally not well adapted to our region.  They’re better adapted to areas where the summers don’t get quite so hot; where the soils are more acid and have more organic matter; and where there is snow over the roots during the cold parts of winter.  In their native habitat you’re most likely to find them at cooler, higher altitude locations growing close to water.

Birch Tree Roots Need Air

Birch trees have a rather large system that can spread twice the distance of the tree’s height or more!  A mature tree’s root system can be as large as one-third the size of a football field.  Obviously, birches need room to grow and shouldn’t be planted in areas that restrict their growth.  Small planting areas or sites close to sidewalks, driveways, and building foundations should be avoided. 

Compacted soils limit air getting to roots.  When planting birches you need a soil that has not been compacted by construction equipment.  Compacted soils should be “ripped” or deeply cultivated before planting birches.  (Keep in mind that you need to loosen the soil in an area about one-third the size of a football field.)  If the soil becomes compacted after planting due to traffic from people, pets, or vehicles or due to the use of impact sprinklers, aeration is a must.  Aeration will help get air to the roots and keep the trees healthier.

Birch Trees Need Water

Remember, in their native habitat you will most likely find birches associated with a water source... rivers, streams or lakes.  Watering a birch tree just with your lawn irrigation is inadequate.  Birch trees need much more water than the leftovers they receive from lawn watering. This means watering the trees once a week during the hot part of summer and once every two to three weeks during the cooler parts of the growing season.  Watering deeply with a soaker hose placed at the dripline (the perimeter of the branches) is what’s needed.  After watering deeply the soil should be moist to a depth of 18 to 24 inches.  Watering should continue until the end of October.  If the winter remains mild and warm, then it’s also recommended to water at least once a month if the soil becomes dry.

While it would be very hard to mulch the entire root system of a mature tree, young birch trees benefit from mulching the root zone with bark chips or compost.  This helps maintain soil moisture and keeps the roots cooler.

Birch Trees Need It Cool

“Coolness” or mild summer temperatures are not something we can control, but we can avoid planting birches in sites where they will be under additional heat stress.  Don’t plant them on south or west facing slopes.  Don’t plant them where they’re surrounded by paving or asphalt.  Don’t mulch them with stone or rock mulches.  Avoid planting birches where they’ll also be exposed to strong, drying winds.  Shelter them from wind and sun on the north sides of buildings or with other trees.

Is It Decline or Is It Borers?

Too many birch trees in our area are declining and dying back because they’ve experienced considerable stress.  This stress and subsequent decline of the birches has been the result of inadequate or improper watering, compacted soils, and damage to the roots from cold winter and hot summer temperatures.

Identifying Bronze Birch Borer

The weakened state of local birches has made them very vulnerable to attack from the bronze birch borer.  This is a wood boring beetle pest that is decimating many local birches.  The first symptom of bronze birch borer attack is the wilting and dying back of the top portion of the tree.  However, this is pretty much the same symptom that results from the general decline of the tree. 

To determine if the bronze birch borer is at fault, an examination of the main branches and trunk at top of the tree needs to be made.  The bark will be bumpy and ridged from the borer larvae feeding beneath the bark.  Slicing into the area right below the bumpy bark will reveal serpentine trails filled with the dark excrement of the feeding larvae.  Once the feeding larvae mature they pupate and turn into adult beetles.  The adults exit the tree leaving characteristic D-shaped holes in the bark. These holes are sure signs of bronze birch borer activity.

Resistant Varieties

What can be done to control bronze birch borer in our birches?  Well, the very first thing is to plant trees that are more resistant to attack from the borer.  Unfortunately most of the types of birches planted in our area are very susceptible to bronze birch borer attack.  This includes the European white birch (Betula pendula,) Jacquemonti Birch (Betula jacquemontii,) and Young’s weeping birch (Betula pendula ‘Youngii’.)  The River birch (Betula nigra) and the Heritage birch (Betula nigra ‘Heritage’) are probably the most resistant birches available.  Unfortunately, the River birch and Heritage birch don’t have the much-desired white bark.  Instead they have an attractive peeling apricot colored bark. 

The Whitespire senior birch (Betula platyphylla japonica `Whitespire Senior’ is moderately resistant and does have white bark.  However, it’s important to get `Whitespire Senior’ that has been propagated from the original, superior tree in Wisconsin.  Other trees that are simply designated as “Whitespire” may be seedling trees that are probably not resistant to the borer.

Managing Bronze Birch Borer

If you chose to plant a tree that isn’t resistant to bronze birch borer, your next line of defense is to keep the tree as healthy as possible and growing vigorously.  Plant the tree in a suitable location where the soil can be kept cool and moist.  The north or east side of your home is best.  Be sure to water deeply during the growing season, especially during the hot part of summer.  Mulch the roots with shredded bark, wood chips or coarse compost.  Don’t use rock mulches!

Fertilize the tree to maintain vigorous growth if needed.  Use a slow-release tree fertilizer and be careful not to over-fertilize.  Don’t prune birch trees unless there is a very good reason to prune.  When you prune, avoid pruning in late winter or early spring because the sap will bleed.  Absolutely do not prune until July during the growing season because adult female bronze birch borers are attracted to trees with fresh pruning wounds. 

Chemical control of bronze birch borer is difficult.  Pesticide applications are best applied to the bark to prevent reinfestation by adult borers that have already emerged.  By the time a borer attack is evident, chemical pesticides will have limited or no effect on borers feeding under the bark.  To prevent reinfestation the recommended sprays are applied to the bark and the leaves.  These should be applied in late spring and early summer (May through June.) They must be applied with thorough coverage to the bark because the adults lay their eggs under loose bark and inside bark cavities.  Timing is critical to get the adult beetles and the baby larvae before they eat their way back under the bark where they’ll spend the rest of the summer feeding.  In the fall they pupate or transform into a resting stage just underneath the bark for the winter.  In the spring they mature and transform into adults and then emerge... leaving D-shaped holes.

Systemic insecticides applied to the soil for uptake by the roots or injected into the tree usually have no or only limited effectiveness on the borer larvae in the tree.  The systemic insecticides which do provide some control are only effective when the larvae are actively feeding in the summer and early fall.  Spring and fall applications of these systemics is not practical.

If a birch tree has been infested by bronze birch borer, it’s also important to prune out infested wood as soon as possible.  Pruning cuts should be made properly well below the infested area.  Infested wood should be destroyed or disposed of as soon as possible.

Leaf Scorch

Leaf Scorch

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Hot weather or drought conditions sometimes lead to a physiological problem called leaf scorch. Leaf scorch shows up as a browning and drying of the leaf edges. In severe cases the brown areas will extend into the leaf tissue between the main veins. In extreme cases, the entire leaf turns brown.

Leaf scorch is often more severe on the side of the plant where the heat stress was greater, usually the south or southwest sides. Reflected light from light-colored surfaces and heat radiated from cement or asphalt put additional heat stress on plants and can increase the severity of leaf scorch. Rock mulches also absorb and radiate heat causing plant stress.

Leaf scorch is associated with inadequate amounts of water being available for the plant to use, especially during hot weather when plants have higher water demands. However, the cause is not always a matter of heat stress and too little water in the soil. A number of other factors may contribute to the development of leaf scorch. These factors include:

Inadequate or poorly developed root systems due to recent transplanting or poor planting practices.

Girdling roots choking the tree.

Injury to the roots or trunk, especially mower and weed trimmer injury.

Vascular disease.

Root disease, especially root rot.

Interference with water uptake and utilization due to soil compaction, poor penetration of water into the soil, water run off on slopes; and high salts in the soil.

Excess water and saturated soils exclude oxygen from the roots and also interfere with root function and water uptake. The result of too much water can be the same as too little!

Leaf scorch is a sign that a tree is under some sort of stress. When scorch develops on tree leaves, it's important to analyze the cause and then take remedial action to alleviate the stress and keep the tree as healthy as possible.

Scale Insects

Scale Insects

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Scale insects are positively insidious. As female scale insects mature, they settle down to feed on a plant, hiding beneath a convex shell-like scale covering.  The female scales never move again.  Concealed beneath the armor-like scale, they often go unnoticed because they don’t move and they don’t look much like insects.

Damage

You might wonder what damage is caused to plants by these sneaky little creatures.  Scales feed by sucking sap from plants.  While a few scales won’t harm a plant, large numbers weaken it.  A heavy scale infestation can make a plant more prone to damage from drought or severe temperatures and make it more susceptible to attack from other insects.  Heavy scale infestations can also lead to the death of branches and limbs or possibly an entire plant.  Some species of scale inject a toxin into a plant as they feed, causing even greater damage. 

Certain types of scale suck out more plant sap than they can use.  They expel the excess sap as a mixture of liquid and sugar called “honeydew”.  The sticky honeydew is not harmful, but it can serve as a food source for the “sooty mold” fungus.  Sooty mold is a black fungus that lives on the secreted honeydew, coating leaves or needles and detracting from a plant’s appearance.

Life Cycle

If the adult females don’t move once they start feeding, one might wonder just how they spread from plant to plant.  Before we can answer that question, let’s take a look at the life cycle of scale insects. Most scale insects start their life as eggs.  These eggs hatch and become immature scales, also known as nymphs.  These immature scales are mobile and referred to as “crawlers”.  The crawlers have six legs and walk around looking for a place to feed on the new plant growth. 

When they are ready to settle down and feed, the crawlers molt and begin forming the scale over their bodies.  They produce this scale covering from waxy filaments and feces.  The shape, color, and size of the scale are distinctive for each species of scale.  The scale covering provides protection from being eaten by other insects... and also from being killed by insecticide sprays.

Once the female scales have settled down to feed and secreted the scale covering over their backs, most species lose the use of their legs.  Male scales are different.  They develop under thin scales and emerge as winged forms.  Their only purpose in life is to mate.  They have no functional mouthparts and can’t feed.  After they mate, the males disappear.  The females then produce eggs (some species produce live nymphs) under their scale covering or in some type of cottony material... and thus the cycle of lives begins again.  Most species of scale that attack outdoor trees and shrubs in our region have only one generation a year.  However, scale insects found on indoor and greenhouse plants can produce several generations a year. 

It is in the crawler stage that scales move from plant to plant, but the tiny crawlers can’t fly and aren’t able to crawl or walk to different plants.  They are moved about in different ways. Their mode of transportation can be the wind, other insects, birds, animals, or even man.

Managing a Scale Infestations

Managing a scale infestation is not an easy task.  Because of their sneaky nature, scale populations tend to build up to large numbers before they’re noticed.  It’s also especially difficult to control these insects because their scale protects them from most insecticides.  Some scales can be controlled with dormant oils applied in late winter.  The oils work by suffocation.  However, it’s in the unprotected crawler stage that scales are most vulnerable to control with insecticide applications.  The problem is that the crawlers are so small it’s difficult to detect their presence and there is a relatively short time before they start covering themselves with a scale. 

A magnifying glass or hand lens will assist you in seeing them.  You can also trap crawlers with double-sided sticky tape wrapped around twigs and branches.  About the time when the crawlers are expected to emerge, place the tape near adult scales and trap the crawlers as they move out to feed on new growth. You may need to renew the tape from time to time, when it loses its stickiness.  Keep an eye on the tape and apply the appropriate sprays when they emerge. 

Scale Insects Troublesome to Trees & Shrubs in Our Region

Pine Needle Scale: This scale is a often problem on stressed pines, especially older trees or those located in dusty areas.  Pine needle scale is white, pear-shaped and about 1/8 inch long.  Its feeding weakens and slows growth.  Pine needle scale can be controlled with dormant oil applied in the spring before new growth begins and with sprays at the crawler stage about April.

Spruce Bud Scale: More and more of this sneaky scale is showing up in local spruces.  It’s often found on the lower branches of spruce trees, but it’s not easily noticed because the scales resemble spruce buds and are located at the base of new twig growth.  Gardeners sometime notice the excessive amounts of honeydew produced by this scale; the bees and wasps attracted to this copious sweet residue; or the sooty mold growing on the honeydew.  However, it may not be noticed until dieback starts occurring.  Spruce bud scale can be controlled with delayed dormant oil in the spring and with sprays when the crawlers appear about June. (Be aware that oil sprays will turn a “blue” spruce to green.)

Juniper Scale: Here’s a little round scale that feeds on the needles of juniper, arborvitae, chamaecyparis, cypress, and red cedar, but it’s most often seen on juniper in this region.  The scale is off-white with a central yellow dot. It tends to be a problem on older, less vigorous junipers.  It can be controlled with dormant oil in late March to early April before new growth begins and with sprays when the crawlers appear about June.

San Jose Scale: This is also a very small scale (1/16 inch in diameter) round scale.  It attacks a wide variety of hosts including apple, cherry, pear, poplar, willow, maple, birch, and many other deciduous trees and shrubs.  It’s black and tends to blend in with the bark of many trees and shrubs. 

This is a common problem on fruit trees and is moved about by the wind, birds, and humans.  Predators sometimes keep small populations of San Jose scale under control, but rampant infestations can be quite damaging.  Control can be achieved with late winter dormant oil and with sprays when the crawlers appear in June and again in September.

Other types of scale sometimes found in this region include cottony maple scale on maples, oystershell scale on various deciduous trees and shrubs, elm scale on elm, and hemlock scale on spruce.

If you should notice some scale on one of your trees and shrubs, don’t panic. Many scale infestations are kept under control by natural enemies.  Sprays may not be warranted if predators or parasites have kept the population in check.  There are also cultural controls that gardeners can employ to assist with prevention and management.  First and foremost, keep your plants happy and healthy.  A tree or shrub that’s growing vigorously and not stressed will be less prone to attack.

The Use of Imidacloprid for Aphid Control in Trees

The Use of Imidacloprid for Aphid Control in Trees

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Late winter is a good time to apply imidacloprid to shade trees for control of aphids in the coming season.  Imidacloprid, know commercially as Merit, is available to home gardeners under the name of ABayer Advanced Garden Tree & Shrub Insect Control Concentrate@.  It=s a liquid material that you mix with water in a watering can or bucket and then apply it to the soil at the base of the tree trunk.  It=s taken up by the tree and transported to the leaf tissues where it controls a variety of sucking insects, especially aphids. The amount applied is based on the circumference of the trunk at chest height. 

It takes a while for the chemical to reach the tops of tall trees... so late winter is a great time to apply the imidacloprid so it will be available when the leaves bud out and the early aphids start feeding.  The product is quite expensive and you may have sticker shock after you determine the amount you=ll need for larger trees, but it provides 12 months of control.  It=s also more environmentally sound, eliminating the difficulty of spraying the tops tall trees and removing the possibility of spray drift.  Beneficial insects are also protected by this method of application. 

Imidacloprid is also a good material for season long aphid control in roses.  However, the ABayer Advanced Garden 2 in 1 Systemic Rose and Flower Care@ contains fertilizer and a different systemic, disulfoton, that will only be effective for six weeks or less. It=s applied as a granular to the soil.  For season long aphid control on roses, use imidacloprid applied to the soil.  Just keep in mind that

Control Options for Trees with Sycamore Blight

Control Options for Trees with Sycamore Blight

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

Living in Prosser and working in the Tri-Cities, I have often been able to notice a distinct difference in the climates of each area.  This spring the disparity between the two has become very evident because of a disease problem showing up on sycamore trees. The sycamores in the Prosser and Grandview area have been hit hard by sycamore anthracnose, also known as sycamore blight.  It=s a fungus disease that attacks sycamore buds, shoots, twigs, and leaves. 

Our native sycamores, the western sycamore (Plantanus racemosa) and the American plane tree (Plantanus occidentalis), are very susceptible to sycamore anthracnose, a fungus disease common in this region.  The Oriental plane tree (Plantanus orientalis) and the original (not seedling offspring) London plane tree (Plantanus acerifolia) are more resistant, but not immune.  Resistant cloned cultivars include >Bloodgood=, >Columbia=, and >Liberty=.

This fungus attacks new tissues when they begin to emerge in the spring.  Infection is most severe when the weather is wet and cool with temperatures below 55 degrees.  Depending on the timing of the infection, the fungus may infect and kill expanding bud, shoot, and leaf tissues before they fully develop or it can attack leaves later after they=ve expanded.  On leaves, the fungus creates brown lesions that form along the midrib and main veins of the leaf. 

Cultural Control

Cultural control of the disease consists of raking and destroying fallen leaves and twigs along with keeping the tree adequately watered and fertilized.  On smaller trees it=s recommended to prune out and destroy infected twigs and branches.  Cankers on these infected branches provide spores for future anthracnose infections.  However, removal of cankers by pruning is impractical on large, older trees.

Fungicide Applications

Fungicides to prevent infection can be applied, but these are sprayed onto the tree when the buds begin to swell and the bud caps first start to break.  They are applied again 10 days after the first spray. Timing and good coverage over the entire tree is critical in getting control... something that=s very difficult with big trees.  

Injections for Control

One other control option is available.  This is an injection of a systemic fungicide into the tree.  This is done by drilling small holes into the trunk or root collar of a tree and injecting the material into the tree.  The fungicide is carried through the water-conducting vessels in the wood to the branches and leaves where it will protect against early season infection.  

To be effective this is usually done for two consecutive years.  Some materials are injected in the fall; other materials require an early spring application.  This procedure should be done only by a professional arborist trained in proper injection techniques.  Repeated use of this method may lead to eventual significant damage and wood rot because of the holes that are drilled into the trunk.

Stopping Wormy Fruit in Cherries and Apples

Stopping Wormy Fruit in Cherries and Apples

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

There seems to be a great deal of confusion about the need for spraying fruit trees to control insects and diseases.  There are a number of pest problems on fruit trees that require frequent and regular chemical applications to keep the trees healthy and producing quality fruit.  When fruit trees are large, this becomes a difficult, costly, and time-consuming responsibility for their owners.  Smaller, dwarf trees are easier to handle, but still require regular attention.  Owning and caring for fruit trees is not a low maintenance endeavor.

One of the major pest problems faced by backyard fruit growers... the cherry fruit fly.  It’s first and foremost on the list because it’s the pest that causes worms in cherry fruit.  The adult of this pest is the cherry fruit fly.  The adult is a fly that begins to emerge from the ground in late may or early June.  The adult fly takes about seven to ten days to fly around and mate.  After mating, the female lays eggs underneath the developing cherry’s skin.  (No hole is visible in the cherry after she lays the egg.) 

The eggs hatch into small larvae, actually maggots, and begin feeding close to the pit. After about five to eleven days, the maggots each make one or two breathing holes in the skin. (These holes are small but visible.)  Several days after making their breathing holes the maggots are fully mature.  They exit the fruit and drop to the ground where they go into their resting pupae stage.  They spend the rest of the year as pupae in the soil until next spring.

While eating one of these maggots (yuk!) won’t hurt you, it’s certainly not appetizing.  An entire load of commercially grown cherries can be rejected if even one larva is found.  Control of the cherry fruit fly is aimed at killing the adult fly before she lays her eggs under the cherry’s skin.  Once they’re under the skin, pesticide sprays are useless in killing the developing maggot.  That’s why it’s so important to spray regularly and get rid of the flies before they have a chance of laying eggs.

To control cherry fruit fly, backyard cherry growers should recommended sprays regularly, every seven to ten days starting about Mother’s Day weekend..  (Remember, you can’t tell by looking at them whether cherries contain maggots or not.) 

If you’re doing a good job of controlling the cherry fruit fly in your yard but you have a neighbor who isn’t, you may still get maggots in your fruit.  That’s because the flies from your neighbors’ trees are capable of coming over to your tree and laying eggs after you spray.  That’s why it’s important for all backyard orchardists to control this pesky fly... as they cause problems to others growing cherries including the many commercial cherry growers in this area.

Let’s move on to worms in apples.  This is a very different insect pest... the adult is a moth.  Worms in apples are the result of codling moths.  The adult moths emerge sometime in May... about 14 to 21 days after the tree was in full bloom and start laying their eggs on leaves and the surface of developing apples and pears. (They also may attack quince, crab apple, hawthorne, and English walnut.)  It takes anywhere from six to twenty days for the eggs hatch into little larvae.

Once they hatch, the codling moth larvae chew their way into the fruit and proceed to eat their way to the center and eat on the seeds.  As they start to mature, they eat their way out of the fruit, usually exiting at the base.  They then find their way to the branches and trunks to spin a cocoon under loose bark or other little hiding places.  They pupate or go into their resting stage in the cocoon.  There are usually two generations of codling moth a year, but there can be three during longer, warmer seasons.

Control of codling moth is aimed at killing the baby larva before it enters the fruit.  Since it chews on the skin of the fruit before entering, pesticides applied to the fruit will kill the larva both through direct contact and through ingestion.  Because there are at least two generations a year, pesticide applications must be made regularly starting soon after adults start laying eggs and continuing through the summer.  Spray apples and pears on a regular basis with the recommended material starting when codling moths are present and laying eggs.  That’s usually two to three weeks after full bloom... usually around Mother’s Day weekend.

Things you should know about controlling cherry fruit flies and codling moths:

1. Dormant oil and dormant fungicide sprays do not control either pest.  They control overwintering insects, such as aphids and scale.
2. Good coverage of the tree with pesticide spray is important. Start at the top of the tree and thoroughly cover the tree just to the point of runoff. Spray the leaves, fruit, limbs, and trunk.
3. Don’t spray when it’s windy.
4. Don’t spray when it’s hot... over 85 degrees Fahrenheit.
5. Avoid wetting the leaves with irrigation sprinklers right after applying the material.

Aphids Are Nasty Little Suckers

Aphids are nasty little suckers.  Yep, that's right they can suck the life right out of a plant. Severe infestations of aphids can even lead to a plant's demise by weakening it and making it more susceptible to attack from other insects and more vulnerable to injury from environmental stress. Some types of aphids inject toxins into the plant as they feed, causing distorted and malformed growth. Certain aphids even spread disease as they move from plant to plant.

Appearance

Aphids are soft-bodied insects with a pear-shaped body.  Different aphids come in different colors... green, black, grey, red, purple, and yellow.  Most aphids you'll find on your garden plants don't have wings, but at certain times of the year they do develop wings.  Aphids are fairly slow moving insects so it's not hard to check them out.  Look for their Acornicles@, a pair of tail pipe-like structures projecting out from the rear of their abdomen.

Sucking Sap

While small, aphids are successful at what they do... they suck sap from plants.  They do this by pushing their tiny stylets (located in their proboscis) into stems, leaves, and even roots.  You might think the stylets are tough to be able to pierce plant tissues, but they're aren't. To protect their thin stylets the aphids secrete a fluid that forms a hard protective coating over them as they push into the plant.  Once the stylets tap into the phloem, the source of the plant sap, the aphid secretes saliva into the plant.  It's believed that the saliva is produced to counteract the effects of proteins formed by the plant in response to the wound caused by the piercing stylets.

Once the aphids tap into the phloem they have access to the sugary sap flowing through these plant conducting tissues.  Plant sap contains lots of sugar, but not much of other nutrients needed by the aphids to survive.  To get the nitrogen they require, aphids must imbibe much more sugary plant sap than needed to sustain themselves.  As a result, they excrete volumes of a sugary liquid, called honeydew, from their alimentary canal.  This excreted honeydew is deposited on the leaves and appears as shiny spots.  When aphid populations are large, honeydew can entirely coat lower leaves, making them very sticky and shiny.

Reproduction

Of the over 4000 aphid species in the world, only about 250 species are considered pests.  The presence of moderate amounts of aphids on a plant doesn't mean a plant is doomed, but it should prompt monitoring of the situation.  Not only are aphids successful at sucking, they're also veryadept at reproduction.  Several immature aphids deposited on a plant will mature in about a week.  Each of these young aphids is usually a female and able to produce 40 to 60 baby aphids or nymphs.  These babies quickly mature and then reproduce, setting off a real baby boom with the population having the potential of growing into the hundreds and thousands quite quickly.  If they become too crowded on a branch or the plant becomes weak andAtapped out@, some of the aphids will develop wings and go off to start new colonies.

Life Cycle

The life cycle of many aphids is pretty straightforward.  Aphids go through simple metamorphosis starting out as an egg and hatching into a nymph in the spring.  The nymphs molt and change into successively larger nymphs and then into adults.  During the spring and summer, the females give birth to live babies (all female) who in turn mature and give birth and so forth.  There is usually enough time during the growing season for several or more generations.  When the aphid colony becomes too crowded or the plant starts to die, some of the aphids will develop wings so that they can fly to other feeding locations.  In the fall, some male aphids develop and mate with females.  The females lay eggs for overwintering.

That life cycle may seem simple, but some aphids are Aheteroecious@.  This means they spend the fall, winter and spring on one type of plant species and then spend the summer on an unrelated plant species. That explains the presence of aphid distorted leaves on certain plants but the absence of aphids when the plant is checked for aphids during the summer.  Examples of heteroecious aphids are the rosy apply aphid on apple and plantain and the lettuce root aphid on poplar and lettuce.  Other aphids are Aautoecious@ spending their life on one species of plant or closely related species.

Managing Aphid Infestations

While aphids are nasty little guys dedicated to sucking away at plant sap, light to moderate infestations usually cause no real harm to healthy mature plants.   Control is often desired by gardeners for aesthetic reasons or because the excreted honeydew is creating a problem.  On vegetable crops, gardeners may feel a need to control aphids because their presence diminishes their enjoyment of their produce.  The least toxic way to manage an aphid infestation is the use of a strong force of water from a garden hose to knock the aphids to the ground where most will not be able to crawl back up the plant.   Of course this method is not practical for delicate plants or those without stiff stems.

Summer oils and insecticidal soaps work well against the soft-bodies of aphids. However, be aware that these materials must come in direct contact with aphid bodies because they work by disrupting their membranes.  Soaps and oils don't have any residual effect and must be reapplied when aphid numbers increase again.  If the aphids are protected by distorted and curled leaves, these materials will not work because they don't come in contact with the aphid bodies.  It's also important to note that many aphids feed on the undersides of leaves.  Oils and soaps must be directed to the surfaces where the aphids are feeding to be effective.  Be sure to check for label directions and precautions, such as not using oils in hot weather or using soaps or oils on sensitive plants.

There are also a number of spray insecticides, such as malathion, diazinon, and acephate, that attack the nervous system of the aphids and can provide aphid control.  Adequate coverage is also needed with these materials for them to be fully effective.  However, when you use these materials you will probably also be killing a number of aphid enemies, such as lady beetles, lacewings, syrphid fly larvae, aphis lions and tiny wasp parasites.  These aphid enemies may have been helping you by keeping aphids and other pests in check.  Without their help, pest problems may build to threatening levels.

Systemic Insecticides for Aphid Control

There are also several systemic insecticides that can be used in aphid management.  They're applied to the soil and taken up into the plant sap.  When the aphids feed on the plant sap, they imbibe these and become poisoned.  One advantage to using the root-applied systemics is their ease of application.  They're applied to the soil and taken up by the roots... there's no spraying and very little equipment is needed.

Another advantage to the root-applied systemics is that most of the beneficial insects are not harmed by their use.  Di-syston is one of these materials.  It has been on the home garden market for a number of years and is applied to the root zone of plants as a granular and watered in.  It's a popular material for use in Arose systemics@.  Imidacloprid is another root-applied systemic that just became available to home gardeners a couple of years ago.  It's mixed with water and applied as a drench to the base of a tree or shrub.  It works very well and lasts all season long, but it's quite expensive when compared to oils, soaps, or the spray materials available for aphid control.  Imidacloprid is currently only available to gardeners from the Bayer Advanced Garden products line.  It's in Bayer Advanced Garden Tree & Shrub Insect Control Concentrate@.