Spotted Wing Drosophila and Japanese Beetle Update

July 19, 2017

Bill Hutchison, Eric Burkness, Dominique Ebbenga, and Suzanne Wold-Burkness
MN Extension IPM Program, Dept. of Entomology, University of Minnesota

Spotted Wing Drosophila

Harvest of June bearing strawberries should be complete across the state and in southern Minnesota the harvest of summer bearing raspberries and most blueberry varieties should be coming to end. However, any thin skinned soft fruit that is ripening or ripe at this point (day neutral strawberry, raspberry, blackberry, blueberry, cherry) is susceptible and now at high risk for SWD infestation. Numbers of SWD in traps continue to increase across the state. All traps were positive this week with the highest single trap catch at ~5,000 flies per trap in one week in southern Minnesota. Traps in the Twin Cities Metro are generally between 100-200 flies per trap. Unfortunately, fly numbers could go even higher than 5,000 per trap and management strategies will have to remain in place to protect fruit until the end of harvest. In addition to trying to maintain shorter spray intervals of 5 days and trying to practice clean harvests and sanitation to eliminate excess fruit remaining on plants or the ground, we remind growers to store fruit under refrigerated conditions prior to sale, if possible.  Cooling the fruit can cause mortality to SWD eggs and larvae and will slow development as well. For updated SWD trap catch (sorted by location and berry type) and reference materials on management options, please visit http://www.fruitedge.umn.edu/swd . If you plan to make insecticide applications to manage SWD, please make sure to carefully read and follow the directions on the label of the insecticide.

SWD Trap in Fall Raspberries

SWD trap in a row of raspberries.


Japanese Beetle

The first Japanese beetles of the season were observed on raspberry during the last week of June in Rosemount, MN this year. Populations have been relatively low until the past week. Populations have increased rapidly and winter survival was likely high and has contributed to higher populations this summer compared with 2016. Japanese beetle has a wide host range that includes many types of fruits, including raspberries, apples, grapes, and ornamental plants and trees. Adults are typically active in late June and throughout July with egg lay occurring in July in weedy grass areas or turf and after egg hatch larvae (white grubs) will feed on developing roots in the soil. To view the current distribution of Japanese beetle in Minnesota visit http://www.mda.state.mn.us/plants/insects/japanesebeetle.aspx . If you’ve had issues with Japanese beetle in the past, you will likely have issues this year as well. Spot spraying (only treating areas where the beetles are present) with an insecticide (for example products containing the active ingredient carbaryl) will typically work well.  However, as populations increase, treating an entire crop or planting may be necessary. Because the beetle population can be high in an area this year, reinfestation is likely as the insecticide residues degrade. So an infestation should continue to be monitored until about mid-August when adults begin to die and populations decline. If Japanese beetle traps are used, it is typically a good idea to locate the traps away from the crop to draw them off of the plants you are trying to protect. Please visit http://www.fruitedge.umn.edu/insectpests/jb for information regarding management of Japanese beetle populations. If you plan to make insecticide applications to manage Japanese beetle, please make sure to carefully read and follow the directions on the label of the insecticide.

Japanese Beetle on raspberry fruit

Japanese beetles on raspberry fruit.

Japanese Beetle on raspberry fruit

Japanese beetles on raspberry leaves. Note the characteristic white tufts of hairs on the sides of the abdomen and metallic bronze and green coloration (click on photo to enlarge).