Weather conditions in west central Michigan during the past seven days were hot and dry. Daily maximum temperatures averaged 80 degrees Fahrenheit and the minimum temperature was 61 F. No substantial precipitation occurred during the same period, only scattered showers were present in the region. That increased the need for supplemental irrigation for all small fruit crops, and in blueberries contributed to the problems of soft fruit at harvest.

Blueberries have continued without major problems except for the presence of spotted wing Drosophila (SWD) that is creating considerable loses for some growers unable to maintain tight SWD control. Another problem was high temperatures causing soft fruit problems affecting fruit quality. In counties south of Allegan, we are seeing the end of the Bluecrop harvest and growers are machine harvesting the remaining fruit to clean up the field. Jersey harvest has continued with quality not as good as that observed for Bluecrop. Currently in Allegan County, growers started harvesting the variety ‘Elliott’ with fruit of excellent quality and some fields will have an almost normal crop with very good market prices. Meanwhile in Ottawa County and other northern counties, Bluecrop and Jersey harvest has continued with fruit of good to excellent quality.

The past week has been the most active week for SWD since the beginning of the season, both in blueberries and in all small fruit crops. SWD captures increased from a few flies during the past weeks to more than 20 flies per trap during the past seven days. As a result of this, detections of blueberry fruit infestations at the packing plant increased substantially, despite grower’s intensified efforts to maintain tight SWD control.

During the past week, some growers requested assistance to identify fruit infestations and get advice on their integrated pest management (IPM) program. One observation that is worth mentioning is growers that complained about SWD infestation in fruit did not reapply insecticides right after the heavy rains of Aug. 2 and waited five or more days to apply another spray, or sprayed Mustang Max 24 hours before harvest.

Harvesting immediately after the end of the 24 hour pre-harvest interval (PHI) does not always result in clean fruit. This is because the insecticide may not have penetrated into fruit in a quantity large enough to kill large larvae that requires being exposed to a bigger insecticide amount than small larvae. Although you may start harvesting immediately after the 24-hour PHI, it will be better to wait a few more hours to allow for more time for the insecticide to act, especially under high SWD pressure.

If you are in the middle of harvest and the number of SWD flies in your trap are high, DO NOT use Malathion. Use Mustang Max or any other insecticide with a short PHI. 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 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.

If you need assistance with your selection of insecticides or using MSU Enviro-weather, contact your local MSU Extension office or contact me at 616-260-0671 or garcias4@msu.edu.