Southwest Michigan grape scouting report – August 9, 2016

Veraison is beginning while young vines experience drought stress. A fourth generation of grape berry moth is predicted this year.

Drought-stressed muscat grapes on a third-year vine. Photo: Brad Baughman, MSU Extension.
Drought-stressed muscat grapes on a third-year vine. Photo: Brad Baughman, MSU Extension.

Weather and crop development

With no rain the past two weeks and highs in the 90s last week, conditions have been hot and dry. Some vineyards on well-drained soils are experiencing drought stress, and irrigation should be employed where it is available. Young vines are particularly vulnerable to drought stress.

Many wine grape varieties are entering veraison, and color is also starting to show in Concord grapes.

Growing degree-days base 50 accumulations for the year


Aug. 8

Aug 15. (projected)

Berrien Springs







The third flight of grape berry moth continues with one to nine male moths per trap. Though trap catch is lower during the third flight than during the first two, the potential for damage is higher. In Berrien County, 5-12 percent of clusters had some damage, and 10-40 percent of clusters had damage in Van Buren County, though most of the damage was only single berry stings. The berry stings and the trap catch were most prevalent on the vineyard edges adjacent to woodlots.

If vineyards have not yet been sprayed for the third generation, contact insecticides such as Imidan, Sevin or pyrethroids (Baythroid, Mustang Maxx, etc.) would still have efficacy. A second application of a contact insecticide may be needed to control the entire third generation. Be sure to use a different chemical class from what was used for second generation; rotation will keep us from developing resistance issues in the southwest.

Grape berry moth generation development


Wild grape bloom (approx.)

Beginning of third generation

Progress towards 2,430 GDD (fourth generation)

Berrien Springs

May 28

Aug. 2


Benton Harbor

May 28

July 30



May 30

July 31


A fourth generation of grape berry moth is very likely to occur this year, beginning right before or during harvest. Michigan State University Extension suggests growers and vineyard managers monitor vineyards for third generation damage, and watch MSU Enviro-weather’s grape berry moth model. In vineyards with significant third generation damage, plan for a spray at 2,430 degree-days from wild grape bloom in any vineyards with more than a week to harvest. Don’t forget to check pre-harvest intervals carefully! Where third generation damage is light to intermediate, applying only to the border of 10 rows will be all that is needed.

Potato leafhoppers, grape leafhoppers and Japanese beetles are still scarce where we are scouting, but growers and scouts should continue monitoring for these pests in problem areas.


Continued hot and dry conditions have resulted in low pressure from common infections in the vineyards we scout. We are seeing 5-9 percent of leaves and 2-5 percent of clusters with some evidence of disease, by and large old infections of Phomopsis and black rot. Much of the black rot we saw was in association with grape berry moth feeding.

New infections of powdery mildew and downy mildew will still form on leaves, and downy mildew will spread rapidly on dewy mornings when leaves are not protected. Clusters are now resistant to new infections of most diseases, except that Botrytis and sour rot infections can take hold as clusters tighten up in vulnerable varieties.

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