Michigan spotted wing Drosophila update – July 31, 2018

Cooler weather means more SWD activity; blueberry and other berry crops must be protected against infestation.

July 31, 2018 - Authors: Julianna Wilson, Rufus Isaacs, Larry Gut

Spotted wing drosophila larvae (circled on the right) compared with a blueberry maggot larvae (circled on the left) in a coffee strainer after being extracted from blueberries using the salt test on 7/31/2018. Photo credit: Steve Van Timmeren, MSU Entomology.
Spotted wing drosophila larvae (circled on the right) compared with a blueberry maggot larvae (circled on the left) in a coffee strainer after being extracted from blueberries using the salt test on 7/31/2018. Photo credit: Steve Van Timmeren, MSU Entomology.

As predicted last week, cooler weather has meant a lot more SWD activity – especially in unmanaged fruit plantings. Seventy-five sites across the fruit production regions of Michigan were monitored for SWD last week, with an average of 34.5 flies per trap overall, 25 percent more flies per trap than during the previous week. Although the number of spotted wing Drosophila (SWD) caught in traps in managed fruit plantings remained steady, traps in unmanaged blocks caught dramatically higher numbers of SWD flies over last week and fruit tested with the salt method from these unmanaged blocks were infested.

As always, the risk of infestation is highest near the edges and when there are alternate hosts like blackberries, honeysuckle and buckthorn in those adjacent areas. Pressure from this pest can be reduced through sanitation techniques such as exclusion, rapid harvest, and removing and disposing of infested fruit, but at this stage, these cultural controls will likely not be sufficient for effective control on most farms.

For best results for late season control of this pest, it is imperative that growers with ripening or ripe fruit maintain tight spray intervals to continue preventing infestation in managed blocks – particularly in blueberry and raspberry plantings. Be sure to use insecticides rated excellent against SWD to protect fruit, calibrate your sprayer to maximize coverage, and rotate insecticide chemistries to prevent the risk of developing insecticide-resistant populations of SWD on your farm.

We will continue to report on our SWD monitoring program for a few more weeks. Our general reports provide an overview of the situation but monitoring flies on your own farm provides a more relevant source of information on SWD activity. We are also recommending that growers check their fruit for infestation through the season.

For the recently released guide to SWD management in organic systems, click here:  http://www.ipm.msu.edu/uploads/files/SWD/SWDOrganicBerryCrops.PDF

For more information on effective insecticides registered for use to control SWD, refer to the MSU Extension Michigan Fruit Management Guide for 2018 (E-154).

Tags: msu extension, spotted wing drosophila, swd


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