Michigan grape scouting report – May 31, 2016

Warm weather in southwest Michigan has increased grape shoot growth.

Weather and grape development

Warm weather has taken shoot growth forward with vigor in Van Buren and Berrien counties. Juice grapes are at 12- to 18-inch shoots, while most wine grapes are at 6- to 12-inch shoots. Recent repeated rains created disease infection conditions. Wild grapes are in full bloom this week, and bloom in Concord and Niagara will likely begin this week, necessitating pre-bloom sprays for all fruit diseases.

Growing degree-day base 50 accumulations

Location

May 30

Jun 5 (projected)

Berrien Springs

515

608

Lawton

593

700

Diseases

The degree of infection from leaf and shoot diseases has been low. Phomopsis infections that occurred when shoot tissue was first emerging several weeks ago are now visible on shoot bases. Some areas are beginning to show early black rot lesions. Downy mildew lesions may begin appearing soon on any infected leaves.

Bloom in Concord and Niagara is expected to begin later this week. Pre-bloom sprays should be applied to protect against all major diseases of grape clusters, including black rot, downy mildew, powdery mildew and Phomopsis. At this period, tank-mixes of two or more fungicides, or pre-mixes, are an appropriate treatment, as we are entering the most vulnerable stage of infection for the fruit.

Insects

According to the Michigan State University Enviro-weather grape berry moth model, our estimate of full bloom dates in Berrien County is May 28, and in Van Buren County is May 30. Grape berry moth males were caught at all the farms we scouted in Van Buren County (65 to 230 moths per trap) and Berrien County (one to 10 moths per trap). We are currently at the peak of the first flight. MSU Extension suggests growers scout vineyards for webbing in the clusters; if more than 3-5 percent of clusters have larvae, a contact poison is recommended 10 days post-bloom. Most growers, however, can wait to spray until second generation egglaying, which will likely occur near the end of June. Check the grape berry moth model using your farm’s wild grape bloom date or the county estimate.

Recently, we detected grape plume moth (less than 1 percent of shoots infested) at one Berrien County farm. We are also seeing tumid gallmaker feeding on young leaves. Growers should keep an eye out for this pest as we have seen an increase in some vineyards over the past couple of years. Movento applied in mid- to late June when the canopy starts to fill in has been effective for controlling grape tumid gallmaker.

Rose chafers, potato leafhoppers and grape leafhoppers have not been detected, but growers and scouts should begin monitoring for these pests now.

Grape mealybugs have increased in some wine grape vineyards, and wine grape growers should scout for this insect and consider using an effective chemistry to protect vinifera varieties from mealybug and the associated grapevine leafroll virus. Any wine grape grower seeking more information on grape mealybug can attend the upcoming meeting on viruses and mealybug Thursday, June 2, 3 p.m., at Lemon Creek Winery, 533 E. Lemon Creek Rd., Berrien Springs, MI 49103. Email .(JavaScript must be enabled to view this email address) if you plan on attending.

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