Southwest Michigan grape scouting report – July 12, 2016

Disease pressure remains low and leaf-feeding pests are few. Apply contact insecticides now to control grape berry moth.

Weather and development

Concord berries are nearing berry touch, and wine grapes are in varying stages of berry sizing.

Growing degree-day base 50 accumulations for 2016

Location

July 12

July 18 (projected)

Berrien Springs

1,347

1,484

Lawton

1,473

1,616

Insects

We are catching low numbers of grape berry moth males, and second generation egglaying is occurring across most of the grape production areas in southwest Michigan. Levels of damage have been very low (0 to 4 percent of clusters, generally one sting only) at the vineyards we scouted. The application window is closing for using insecticides like Intrepid, Altacor or Belt that are applied at the beginning of egglaying to be most effective.

If vineyards have not been treated yet for second generation grape berry moth, contact insecticides such as Imidan, Sevin or pyrethroids (Baythroid, Mustang Maxx, etc.) should be applied. The Michigan State University Enviro-weather grape berry moth model predicts the start of egg-hatching presently, so we are in the ideal window for using these materials. A second application of a contact insecticide may be needed to control the entire second generation.

Potato leafhoppers, grape leafhoppers and Japanese beetles are out, but are still at very low numbers, or in only a few vineyards. Japanese beetles are generally more abundant in vineyards that are located near large, grassy areas and they can be particularly harmful to wine grapes with tender leaves and a light canopy. Generally speaking, most Concord and Niagara vineyards have dense canopies that can tolerate substantial beetle feeding without affecting the crop. Michigan State University Extension suggests growers and scouts continue monitoring for these pests.

Diseases

The weather has continued to be drier than average, and symptoms of common infections are consistently at very low levels in the vineyards we are scouting. Phomopsis and black rot infections formed during the wet period of early shoot growth continue to develop in many vineyards. Two to 13 percent of leaves are showing symptoms in vineyards we scout. Downy mildew and powdery mildew have not been observed on leaves or clusters at any commercial vineyards we scout.

Juice grapes are now resistant to new infections of black rot, phomopsis, downy mildew and powdery mildew. For the remainder of the season, downy and powdery mildews can form new infections on leaves. Wine grape clusters, on the other hand, remain vulnerable to new infections of most diseases for at least two more weeks.

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