MSU Extension

Most vineyards in Southwest Michigan are rapidly approaching the berry touch or cluster closing phase of development, and with that we know the second generation of grape berry moth larvae will soon appear in vineyards. Egglaying for this mid-season generation begins 810 growing degree days (GDD) base 47 degrees Fahrenheit after full bloom of wild grapes (Vitis riparia) in the area local to the vineyard. Across the region, wild grape bloom was recorded between May 29 and June 2. Using these dates, the MSU Enviro-weather grape berry moth model predicts egglaying to begin in most of the region over the July 4 weekend, or early the following week.

Growth regulator insecticides and other products that are active on eggs and hatching larvae should be applied at the start of egglaying, as close to 810 GDD as possible. For Berrien County, this would be during or soon after the July 4 weekend for insecticides such as Intrepid, Altacor, Belt and Dipel. Contact poisons such as Imidan, Baythroid, Bifenthrin, Delegate and others should be applied at about 910 GDD to target egg hatch timing, which will be a week or so later.

MSU Enviro-weather grape berry moth model summary (GDD47 from wild grape bloom)

Recent high temperatures have increased the rate of development of grape berry moth, and the first flight of adults is ending. There are still a few late first generation larvae in clusters, and we may see early second generation egglaying before those larvae have moved from the clusters to pupate. Very few other pest insects were seen during scouting; rose chafers are no longer present and eastern grape leafhoppers were at very low levels and below economic thresholds. We did, however, record early emergence of Japanese beetles in the vineyards we scout in Berrien and Van Buren counties. Control of Japanese beetles is not needed at this time as the vines have abundant leaf area to ripen the potential crop.

Berry touch also is a critical period for disease control, because as the cluster tightens it becomes more difficult for sprays to penetrate into the center of the cluster. Many growers take advantage of this opportunity to protect clusters from infection by downy mildew, black rot, phomopsis and powdery mildew. This season has proved to be a rainy one, and growers will need to stay on top of disease management. Recent scouting by Michigan State University Extension specialists has turned up some light infections of downy mildew, phomopsis and black rot on clusters, and phomopsis lesions on leaves and shoots. Maintaining protection against these diseases is important as we head towards the fruit ripening stage of the season.

MSU Enviro-weather GDD50 summary from March 1, 2014

Berrien County farms scouted Monday, June 30

Concord has reached berry touch and Vignoles, which have mostly secondary clusters, are now finished with bloom and have small developing berries. Rose chafers were not found during scouting and very few eastern grape leafhoppers, considered below economic threshold, and no potato leafhoppers were seen in the vineyards we scouted. We have recently detected emergence of the first few Japanese beetles; however, there is no need to treat for this pest at this time. A small number of spotted wing Drosophila have been caught in monitoring traps in vineyards, but as this fly attacks ripe fruit, we do not expect any infestation in vineyards at this time.

The first flight of grape berry moth males has declined sharply over the last week, and the number of moths caught in pheromone traps ranged from 0 to 33. Larvae are still feeding on clusters in vineyard hot spots, but these larvae will soon move out of the berries to pupate and metamorphose into adults. Using wild grape bloom on May 29 as the biofix to start the grape berry moth model yields a predicted start date of July 4 for second generation egglaying.

Disease symptoms were still detected at very low levels during scouting in the monitored vineyards on June 30. We found only two Concord clusters in a sample of 100 with early black rot symptoms. The Vignoles were free of disease symptoms. Growers will be applying fungicide and insecticide to protect berries before cluster tightening progresses.

Van Buren County farms scouted Monday, June 30

On June 30, Niagara and Chancellor were close to berry touch. Consistent low captures of grape berry moth males shows the first generation flight is declining, as are the number of larvae in clusters. We expect second generation egglaying by grape berry moth to begin after July 7 in this region. Similar to observations from Berrien County, rose chafers were not found and very low levels of grape leafhoppers were present in the vineyards we scouted. Japanese beetles are starting to emerge, but populations are not large enough to warrant treatment.

We did detect the presence of downy mildew on Chancellor on six out of 50 clusters with two or three diseased berries. In the same vineyard, we also observed early signs of black rot on berries on five out of 100 clusters, and very low levels of early phomopsis lesions were seen on leaves. In the Niagara vineyards we monitor as part of this project, only one cluster with early black rot symptoms was recorded. Growers will be applying fungicide and insecticide to protect berries before clusters become too tight to allow spray penetration.

This report is supported by the Michigan Grape and Wine Industry Council and the National Grape Cooperative.

Drs. Schilder and Isaacs’ work is funded in part by MSU‘s AgBioResearch.