Spotted wing drosophila catches rise sharply in southwest Michigan

Last week we reported that 2018 has been slow to start compared with last season in terms of spotted wing drosophila (SWD) caught in traps. This week, our network of MSU monitoring traps have detected a sharp increase in captures of SWD at farms in southwest Michigan. Some of the traps that were catching just a few flies a week ago are now trapping tens of flies, indicating that the population is increasing quickly with the suitable weather that we have had over the past few weeks.

Average per trap catch over the 90 sites being monitored is up from 0.01 last week to 2.07 SWD flies per trap this week. These are primarily being caught in a handful of southwest Michigan blueberry fields near wild hosts such as mulberry and honeysuckle (see photo). With wild fruit coming into ripeness across this region, SWD will find places to lay eggs and develop even if adjacent crops are not yet ripe.

For tart cherry growers, harvest is looming and given how rapidly the pest can reproduce and how devasting infestation can be, if your crop is at a susceptible stage, do not wait to apply a cover spray of an insecticide that is rated excellent against SWD to protect fruit.

With blueberry growers expecting harvest of the earliest varieties to start around June 29 in southwest Michigan, it will be important to protect ripening and ripe berries to prevent infestation by SWD. Berries that are still green will not need protection until they start becoming ripe later in the summer.

As always, be sure to rotate insecticide chemistries once you begin your spray program to prevent the risk of developing insecticide-resistant populations of SWD on your farm.

We will continue to monitor SWD as the season progresses. Our general regional reports provide an overview of the regional 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, and will be posting a separate article on that later this week.

More information:

• Recently released Management Recommendations for Spotted Wing Drosophila in Organic Berry Crops
• For information on effective insecticides registered for use to control SWD, refer to the MSU Extension Michigan Fruit Management Guide for 2018 (E-154).

– Julianna Wilson, Rufus Isaacs, Larry Gut, Michigan State University

Photo above: Wild hosts like this Tartarian honeysuckle bush, serve as source of SWD next to fruit crops. This week we are finding more SWD adults in traps near wild hosts than last week. Photo: Mark Longstroth, MSU Extension