Timing your black stem borer spray on tree fruits

Guidelines for making your black stem borer treatment decision.

One of the insect pests targeted for management early in the tree fruit season is the black stem borer. Most growers do not have a problem with this pest, but those that do will attest to the difficulty in preventing additional infestations within their orchard. Always look first to correcting the problem, or problems, stressing the trees and causing them to emit ethanol, which attracts the insect. Sometimes it is not a correctable situation, such as stress from a severe winter.

Determining when to spray for black stem borer can be difficult. Ideally, you would use the trapping information for the orchard you wish to protect along with the long-range weather forecast to come up with the perfect time to make your application. Fortunately, there are some guidelines to know when that time approaches. USDA researchers have determined that flight activity generally begins at 100 growing degree-days base 50 degrees Fahrenheit. A phenological indicator is full bloom on forsythia. We have met both these criteria in Michigan’s southwest and Ridge regions and our network of traps are beginning to catch one to two beetles each. At peak flight activity, traps may collect between 10 to 50 or more beetles per week.

If flight appears to be increasing prior to bloom, a Lorsban application as a trunk application can provide the initial protection. Once bees are brought into the orchard, or bloom initiates, all insecticide applications should stop. After bloom, and once pollinators are no longer present, if trapping indicates beetle flight is continuing, another insecticide application should be made. A pyrethroid insecticide would be a good choice as these have been among the top performers in our chemical trials over the past several years. The best way to apply an insecticide for a trunk boring pest such as black stem borer is to make a trunk application versus a full tree airblast application.

More detailed information can be found in the guide “Managing Black Stem Borer in Michigan Tree Fruits” by Michigan State University.

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