West central Michigan small fruit update – July 25 2017

Blueberry harvest is in full swing in all counties. Fruit is of excellent quality and flavor, but pay attention to spotted wing Drosophila management recommendations.

West central Michigan has remained under moderate to high temperature conditions with scattered rain showers, allowing a blueberry harvest with minimal problems. For the past seven days, the average minimum temperature in the region has been around 63 degrees Fahrenheit and a daily maximum averaging 83 F. Precipitation over the same period has been limited to only a few rain showers that left an accumulation of 0.1 to 0.2 inch of rain in the area.

Current weather conditions at harvest time are conducive for the production of high quality blueberries with only minimal problems related to fruit rots or soft fruit problems due to rain or high temperatures at harvest. These conditions, however, are also perfect for reproducing spotted wing Drosophila (SWD) at blueberry and raspberry fields. Thus, we have seen an increase in reported problems with SWD infestations at harvest time. So far, no fruit rejections have been reported.

Because of the reported increased pest pressure, especially at fields having problems harvesting on time due to lack of labor or equipment, Michigan State University Extension recommends the following.

Monitor SWD traps as frequently as possible to timely detect any problems with arriving SWD flies. The main reasons for failing to prevent larval infestations are lack of SWD monitoring traps; inefficient traps unable to detect the presence of SWD flies; and checking traps once a week when they need to be checked at least twice a week due to the intense SWD pressure.

Check the fruit before and after each insecticide application, and before taking the fruit to your processor. Managing and controlling SWD is not a matter of good or bad luck, it is a matter of knowing when and how. Managing and controlling SWD requires timely information of the presence of the pest and weather conditions at the target site. Efficient SWD monitoring (trapping and fruit inspection) allows you to decide when to initiate the control, and the weather information helps you select the insecticide and the time of the application; that is the how. SWD monitoring and weather information provided by Michigan State University Enviroweather is critical for an efficient SWD management.

Finally, selecting the appropriate insecticide according to current and forecasted conditions of rain and temperature is critical to successfully preventing SWD larvae infestations at harvest time. Before programing your next application, check the weather conditions for the next 24-72 hours to determine what class of insecticide you need to use in your field. Remember, pyrethroid insecticides are affected by high temperatures, but are excellent tools at low temperatures and not affected by rain. Lannate and Brigade, and to a lesser degree Imidan, are not affected by high temperatures and remain in the fruit if rains occur after the application.

The extended weather forecast for the next six days indicates temperatures above 80 F and the probability of rain in the area is less than 25 percent, with exception of Thursday, July 27, when the probability of rain is around 65 percent. To maintain SWD populations, Brigade, Imidan, Lannate and Mustang Maxx are a good alternative.

Assail is a good larvicide, but weak against SWD flies. However, it can be used as a “curative” treatment in a rotation with other insecticides. Other alternatives can be found at the MSU Extension2017 Fruit Management Guide,” Bulletin E0154.

If you need assistance with your spray program, call your local MSU Extension office.

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