West central Michigan small fruit regional report – August 4, 2015
Spotted wing Drosophila infestations are increasingly affecting all small fruit crops, but blueberries and raspberries are at risk the most.
Weather conditions for the past seven days have been creating problems for small fruit crops. However, blueberries are the most sensitive to high temperatures and lack of precipitation. During the past week, the daily average maximum temperature was 82 degrees Fahrenheit and the average minimum temperature was 66 F with no precipitation until Sunday, Aug. 2, when most of the central region received between 1 and 1.5 inches of rain. Due to those conditions, some growers reported a decrease in the quality of fruit harvested.
In addition, the presence of spotted wing Drosophila (SWD) in high numbers at all fields in central Michigan is creating management problems for most growers. Since growers need to apply supplemental irrigation to deal with dry weather conditions, SWD control measures had to be scheduled in such a way that irrigation did not interfere with insecticide applications. If overhead irrigation is used, insecticide applications must be scheduled after the supplemental irrigation has been applied.
One major recommendation for this week is that after the heavy rains of Aug. 2, all blueberry and raspberry fields need to be treated again to prevent SWD fruit infestations. Michigan State University entomologist John Wise has demonstrated that 0.5 inches of rain or more substantially affects the persistence of most insecticides used against SWD. Therefore, do not expect to have the same protection you anticipated from your insecticide application performed one or two days before the rain. Reapply your field immediately before harvesting. If you are in the middle of harvest and the number of SWD flies in your trap is low, you may use Malathion. Otherwise, use Mustang Max. However, if you can wait three or more days to harvest, use Imidan, Lannate, Delagate, Danitol or any of the other recommended insecticides with a three-day pre-harvest interval (PHI).
For insecticide options and recommendations, please consult the “2015 Michigan Fruit Management Guide,” (Michigan State University Extension Bulletin E0154), or the “SWD Management Recommendations for Michigan Blueberry” fact sheet.