Increase of spotted wing Drosophila in berry crops

Increasing spotted wing Drosophila catches highlight the need for tighter harvest intervals and excellent berry protection.

Monitoring for spotted wing Drosophila (SWD) over the past week has revealed an upswing in the catches of SWD in monitoring traps. Numbers have gone from a few per trap to some catching more than 10, indicating populations are building and we are entering the time of season when fruit protection from SWD becomes increasingly important. Wild fruiting plants are becoming ripe and the area of ripe fruit in the landscape is higher each week, and both of these factors will drive the SWD population to increase over the next month.

We have typically seen growing populations through July with a sharper increase in late August. This usually means earlier blueberry varieties and the first part of fall red raspberries have less pressure from SWD, but the risk is present and growers should be responding to SWD catches in their local area by taking action to minimize its effect on crops. Michigan State University Extension recommends that if possible, tighter harvest intervals can help reduce the chance for this pest to develop in crops, but this will not be sufficient to prevent infestation of susceptible crops, and chemical control is the primary option being used to control SWD.

Blueberry and caneberry growers have a number of options available for fruit protection, and these are described at the MSU SWD Crop Recommendations webpage. For good control of this pest, if SWD is active and berries are starting to ripen or are ripe, they should be treated with an effective insecticide on a weekly schedule until harvest is complete. Beware of the seasonal limits and the times you must wait between applications. This information is also provided in the tables within the online recommendations.

Scheduling harvest and protection can be very challenging, especially with all the rain. Our research on SWD has demonstrated rainfall causes significant loss of residues and a reduction of control for most products tested, but with Imidan, Lannate and Mustang Max maintaining the greatest amount of activity after rain. These are also three of the most effective insecticides for this pest and represent three different chemical classes, which is important for resistance management. Note that Imidan and Lannate cannot be used in caneberries and Lannate cannot be applied in blueberry fields being used for U-pick sales. We also expect Exirel to be relatively rainfast, adding another chemical class for blueberry growers.

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

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