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.