West central Michigan is still busy harvesting the remnants of blueberries and fall raspberries. Weather conditions during the past week resulted in some of the highest daily temperatures of the summer with daily maximum temperatures averaging 83 degrees Fahrenheit and minimum temperatures of 66 F, with only traces of rain. Those conditions compelled blueberry growers to apply supplemental irrigation to fields that were not yet finished with harvest. Currently, blueberry varieties still in harvest are Elliott and other late-season varieties, but in small quantities. In central Michigan and counties north of Allegan County, harvest will be done soon.

As in past years, the end of blueberry harvest is coinciding with an increase in the populations of spotted wing Drosophila (SWD). SWD is becoming a serious problem for blueberry growers with fields planted with the variety Jersey that are unable to maintain the last harvest relatively free of SWD larvae. Before SWD, fruit from the last harvest was still accepted for processing. However, with an increased number of SWD larvae per load at harvest, that fruit is not accepted anymore for processing, or is downgraded to juice with considerable loses for the grower.

This year, there will be more fields that will not be totally harvested and some fruit will be left on the bush. Although there is not a market for those berries, Michigan State University Extension recommends cleaning the field of any berries that will provide a host for SWD. This will reduce the overwintering population for the next crop season.

Because of the hot and humid conditions of the past two weeks, we have seen a resurgence of SWD populations in the entire region. However, if you are done with harvest, do not spray any insecticide against this pest. This will not have any benefit or impact next year’s populations. On the other hand, if you are harvesting fall raspberries, our recommendation is to limit the amount of overripe fruit in the field that may provide a host for SWD. Harvesting daily will remove a large portion of fruit that could be a host for the flies. Growers need to maintain monitoring of flies and the insecticide application until they consider that is economically acceptable.

For insecticide options and recommendations, please consult MSU Extension Bulletin E0154 “2015 Michigan Fruit Management Guide,” or “Spotted Wing Drosophila Management Recommendations for Michigan Raspberry and Blackberry Growers.”