Advances in management of tree fruit borer pests using mating disruption

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Peachtree borer, lesser peachtree borer, dogwood borer and American plum borer are key indirect insect pests of cherry, apple and peach, in Michigan and other fruit growing regions in the eastern United States. The first three species are clearwing moths while American plum borer is a pyralid moth. The range of cultivated hosts of these four species overlaps, as peachtree borer, lesser peachtree borer and American plum borer are pests of sweet cherries, tart cherries and peaches, while dogwood borer and American plum borer infest apples.

The damage that borer species cause to fruit trees is similar in that they all feed on the phloem and vascular cambium, but each species has its preferred feeding location. The larvae of peachtree borer have a tendency to feed in the lower trunk and roots, a habit that can cause girdling of the trunk and death of young trees. Lesser peachtree borer tends to feed higher in the trunk and limbs, favoring locations such as cankers, pruning wounds and mechanical harvest scars. Dogwood borer larvae enter the trunk of apple trees using burr knots that form when dwarfing rootstocks are used. American plum borer can use harvest scars in cherry, and burr knots in apple. Along with stressing the tree and providing entryways for microbial diseases, borer feeding weakens the trunk and limbs of the tree and can cause them to break under the weight of the crop. It has been estimated that severe borer infestations can kill young trees and decrease the productive life of older trees by one third.

The tree fruit borer species differ in their lifecycle with each species completing a different number of generations and having distinct periods of adult moth flight. Peachtree borer has only one generation per year, the adult flight starts in late spring and peaks in late summer. Lesser peachtree borer has one to two generations in northern fruit growing areas like Michigan. Dogwood borer has only one generation per year and, like with peachtree borer, the adult flight lasts most of the favorable season. American plum borer has at least two generations per year and the flight of the overwintering generation starts as early as late April even in northern areas like Michigan. In a recent survey of borer species in cherry and peach orchards in Michigan, peachtree borer, lesser peachtree borer, and American plum borer were captured in pheromone baited traps in all orchards where traps were deployed.

The occurrence of simultaneous infestations by several species, combined periods of activity extending from May through October, and the sheltered feeding habit of the larvae make this pest complex and difficult to control with conventional insecticides. In addition, only a few effective compounds are registered, and these must be applied as directed trunk sprays that are costly, unpleasant to conduct, and difficult to time correctly. For these reasons, we are developing in Michigan pheromone based mating disruption and attract-and-kill programs to control borer pests in cherry and apple.

Peachtree borers

The discovery of the sex pheromones of peachtree borer and lesser peachtree borer in the 1970’s prompted great interest in their use for mating disruption. Early attempts at mating disruption were successful when each species was targeted separately. When both species were targeted simultaneously, the control obtained was not satisfactory, except if the pheromone for each species was deployed in separate dispensers placed on opposite sides of the tree. Because orchards in the eastern United States are often infested with both species, the excessive cost of deploying two sets of dispensers caused interest in concurrent mating disruption of peachtree borer and lesser peachtree borer to wane.

Recent advances in pheromone synthesis and dispenser technology led to the development of novel dispensers for mating disruption that target both species with a single device. Field trials conducted in Michigan in 2008 compared a new dual dispenser for control of both species with dispensers targeting each species separately. Our results showed 100 percent disruption of male peachtree borer orientation to pheromone-baited traps and 99.2 percent disruption of lesser peachtree borer. These levels of disruption were similar to the ones that we recorded usingseparate dispensers for each species.

Our trials with single and dual dispensers were conducted using 150 dispensers per acre. Other trials comparing disruption of orientation to traps when varying numbers of dispensers were deployed per acre showed that it may be possible to decrease the dispenser rate and still achieve excellent control. We will continue efforts to explore the feasibility of using lower rates in the coming season. These promising advances should improve the efficacy and economics of peachtree borer and lesser peachtree borer mating disruption in eastern cherry and peach orchards.

Dogwood borer

Work done at Virginia Tech and USDAARS showed that the pheromone blend used in commercially available dogwood borer lures contains an antagonist compound that greatly decreases the attractiveness of this blend. This antagonist compound is a byproduct of the synthesis of one of the major components of the blend and its removal has proven difficult to accomplish. The lack of effective lures to trap dogwood borer has hindered the development of mating disruption because male moth flight cannot be monitored accurately.

In Michigan, we initiated collaboration with a chemical synthesis company to custom make a pheromone blend that does not contain the antagonist. This pheromone blend will be loaded into lures that will allow us to accurately monitor dogwood borer flight in mating disruption trials using commercially available dispensers. In addition, we are exploring the possibility of loading the custom made pheromone blend into dispensers for mating disruption. We are focused on finding the most effective and economic deployment rate for the commercially available and new blend dispensers.

American plum borers

The pheromone blend of American plum borer is more difficult to synthesize and use in dispensers for mating disruption than that of the clearwing moths. In Michigan, we are working to test and develop attract-and-kill management options for American plum borer that use less pheromone and do not require loading the pheromone into dispensers for field use. Taking advantage of technologies developed in our research program with codling moth and other tree fruit pests, we are developing traps and toxicant delivery systems that will be effective and economical. Attract-and-kill will require using less pheromone per acre to achieve the same high level of control as mating disruption.

Mating disruption and attract-and-kill management options can be targeted to specific orchard borer species composition and will last the whole season, overcoming some of the major hurdles to effective control. Moreover, the amount of insecticides applied to the orchards for control will decrease, reducing the environmental impact of fruit pest management, and providing long term economic benefit to the fruit industry in Michigan and other fruit growing regions.

Peachtree borer larva
Peachtree borer larva feeding on peach tree trunk at soil level.
Photo credit: L. Teixeira.

Dr. Gut’s work is funded in part by MSU‘s AgBioResearch.

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