Jul 25, 2017

Blueberry growers urged to take stock of SWD pressure

Blueberry harvest is in full swing in Michigan all counties. Fruit is of excellent quality and flavor but growers need to 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˚ and a daily maximum averaging 83˚. Precipitation over the same period has been limited to only a few rain showers that left an accumulation of 0.1 to 0.2 inches 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 the reproduction of SWD at both blueberry and raspberry fields. Thus, we have seen an increase in the number of growers reporting problems with SWD infestations at harvest time. But so far, no fruit rejections have been reported, yet.

Because of the reported increased pest pressure, especially at fields having problems harvesting on time due to lack of labor or equipment, we would like to recommend the following:

1. Monitor SWD traps as frequently as possible to timely detect any problem with arriving SWD flies. One of the main reasons for failing to prevent larval infestations is lack of SWD monitoring traps. Also, 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.

2. Check the fruit before and after each insecticide application, and before taking the fruit to your processor. Growers need to realize that managing and controlling the SWD is not a matter of “good” or “bad” luck. It is a matter of knowing “when and how.” Managing and controlling the SWD require timely information of the presence of the pest and weather conditions at the target site. Efficient SWD monitoring (trapping and fruit inspection) provides the information to make decisions on “when” to initiate the control. And the weather information provides the information to select the insecticide and the time of the application; that is the “how.” So, SWD monitoring and weather information provided by the MSU Enviroweather are critical for an efficient SWD management.

3. Finally, selecting the appropriate insecticide according to current and forecasted conditions of rain and temperature is critical to a successful prevention of SWD larvae infestations at harvest time. So, 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 in a lesser degree Imidan, are not affected by high temperatures and remain in the fruit if rains occur after the application.

Currently, the extender weather forecast for the next six days indicates temperatures above 80˚ and the probability of rain in the area (with exception of Thursday, July 27, when the probability of rain is around 65 percent), is less than 25 percent. So, to maintain SWD populations under control during the next days, Brigade, Imidan, Lannate and Mustang Maxx are a good alternative. Assail is a good larvicide but weak against SWD flies but can be used as a “curative” treatment in a rotation with other insecticides. Other alternatives can be found at the Michigan State University Fruit Management Guide Extension Bulletin E-154.

If you need assistance with your spray program call your local MSU Extension Office. There you will be directed to the right person that will be able to assist you with your questions

 – Carlos Garcia-Salazar, Small Fruit, Agriculture & Agribusiness Institute, Michigan State University