Southwest Michigan grape scouting report – September 20, 2016

Harvest continues with good prospects for weather; consider pre-harvest sprays for insects and downy mildew.

Brown marmorated stink bugs crowd into a trap hanging in a southwest Michigan vineyard. Photo: Keith Mason, MSU.
Brown marmorated stink bugs crowd into a trap hanging in a southwest Michigan vineyard. Photo: Keith Mason, MSU.

Weather and development

Harvest continues in wine grapes and began in Niagara juice grapes. Expect continued warm and dry weather; chance of precipitation is low for the coming week. Highs are predicted to be in the 80s for the rest of the week, dropping to the 70s this weekend.

Growing degree-days base 50 accumulations since March 1, 2016


Sept. 20

Sept. 26 (projected)

Berrien Springs







Fourth-generation flight of grape berry moth is ending. Trap catch of the moths has declined this week and last week, to none to two per trap in Berrien County and one to 16 per trap in Van Buren County. Feeding of larvae from the third generation is now over, and damage is light in the vineyards we scout – 0-6 percent of clusters damaged in Berrien County, and 5-20 percent in Van Buren County.

We have been detecting greater numbers of brown marmorated stink bugs this year in vineyards, though very little feeding damage has been seen. As ripe fruit continue to hang, we are seeing more fruit flies, ants and yellowjackets on the fruit.

For fourth generation grape berry moth and the other insects mentioned above, a final cleanup spray may be needed before harvest in some vineyards. Carefully check the pre-harvest interval (PHI) for this spray and abide by it. We suggest pyrethroid materials, which are broad-spectrum and can be sprayed safely close to harvest.


For most growers, this year has been a relatively low pressure year when it comes to diseases. However, with heavy dews and cloudy weather, we have been through some weather that’s great for the downy mildew fungus. Monitor this situation carefully in all vineyards where more sugar accumulation is needed between now and harvest – another spray for downy mildew will be needed in many vineyards to preserve leaf area.

We are also seeing the typical late season proliferation of botrytis and sour rot in vulnerable varieties, especially in vineyards that didn’t get a botrytis-active insecticide during bloom. Up to 50 percent of clusters are showing some botrytis infections in some Vignoles vineyards, for example.

A final word

This is the final scouting report for the 2016 season. Thanks to many of you for hosting Michigan State University Extension on your farms, thanks for reading, and we hope some things were helpful. Please contact with questions or suggestions for next year’s series, or just to let us know which aspects of the scouting report have been helpful to you. Any notes on your own pest management situation in 2016 would also be of interest to the authors.

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