West central Michigan small fruit regional report – September 2, 2015
Spotted wing Drosophila infestations continue on all berry fields. Blueberry harvest is ending in southern counties, while Elliott and some Jersey fields are in full harvests in Ottawa, Allegan and other northern counties.
The past week presented weather conditions that were optimal for spotted wing Drosophila (SWD) control with some of the most effective insecticides being Brigade and Mustang Max. On average daily maximum temperatures were 72 degrees Fahrenheit and minimum temperatures were 56 F with scattered rains amounting to a less than 0.25 inches. Under those weather conditions, pyrethroid insecticides provide an excellent SWD control. In addition, the end of harvest of most early blueberry varieties in southern counties is leaving the SWD with a reduced number of hosts. At this time only Elliott and other late season varieties are actively harvested and the size of the SWD habitat is shrinking due to the impact of winter on the 2015 berry crop. A better control and limited food resources may have caused a decline in the number of SWD flies trapped by Michigan State University Extension and other scouts during the past week.
However, in spite of this good news, this week we may see a resurgence of SWD populations due to high temperatures and high relative humidity expected for the rest of the week. Those conditions are optimum for SWD population development. Since blueberry harvest may continue for another three more weeks, growers in Ottawa, Allegan and other northern counties need to maintain an active SWD control. It is important to rotate insecticides to prevent the development of insecticide resistance in the SWD and excessive insecticide residues on harvested fruit. Also, to comply with the label recommendation about the number and amount of product allowed per season.
For insecticide options and recommendations please consult the 2015 Michigan Fruit Management Guide (Michigan State University Extension Bulletin E-154) or the MSU SWD recommendations for Michigan Blueberries factsheet.