Southwest Michigan grape scouting report for September 7, 2015

Harvest is quickly approaching in southwest Michigan grape vineyards.

Berrien County farms visited Friday, Sept. 4

Concord is in late veraison and the largest berries are near 2 centimeters in diameter. Concord harvest is estimated to begin around Sept. 25-28. Vignoles are ripening steadily with harvest expected to begin after Sept. 15.

The third flight of grape berry moth males is continuing, but over the past two weeks the number of moths caught in traps has been steadily decreasing. On the last scouting visits to these farms, captures ranged from zero to four moths per trap, indicating the third flight is ending.

Grape berry moth control appears to be good in vineyards we visited this week. Some clusters on the outermost vines on vineyard borders have grape berry moth infestation, but much of this damage involves only a small entry wound on a single berry with no further increase in the severity of damage, indicating that young larvae have been killed. In the vineyards we scouted Sept. 4, infestation ranged from 8 to 74 percent of clusters with higher incidence of damage adjacent to woods containing wild grape. As we have seen all season, very little damage was recorded on vines in vineyard interiors. Harvest is quickly approaching, so Michigan State University Extension recommends growers and scouts check vineyard hotspots to determine if a clean-up treatment for grape berry moth is required. Insecticides with a broad range of activity and a short preharvest interval (PHI) should be used for clean-up sprays. Third generation egglaying and feeding by young larvae is still occurring, but this activity appears to be declining.

Although our recent hot weather has added growing degree days and sped the development of insects, we do not expect a significant fourth generation of grape berry moth before harvest. This is because when grape berry moth eggs and young larvae are exposed to day lengths that are less than 14 hours, the vast majority won’t develop into adults, but will instead enter a resting stage that prepares them for over-wintering. When egglaying began in early August this year, the day length was only about 13.5 hours per day, therefore most of these eggs should not develop into adults, but rather they will enter their over-wintering phase – and yes, you will probably see them next spring!

Japanese beetles and new feeding damage were not seen during scouting this week. Overall, beetle numbers are still low, but growers with susceptible vinifera and hybrid varieties should still scout regularly to check for increasing Japanese beetles and plan to treat and protect areas with heavy beetle activity. Potato leafhoppers and Eastern grape leafhoppers were not seen during scouting at these farms, and their population is not expected to rebound this season. We have seen an increase in the number of common fruit flies and ants in some vineyards with split berries, but the other insect pests that can appear at harvest time, such as multi-colored Asian lady beetlesbrown marmorated stink bugswasps and mealybugs, were not seen during our scouting. We are still catching spotted wing Drosophila (SWD) in traps on vineyard borders, but we do not expect SWD to pose many additional problems.

These vineyards were last scouted for diseases on Sept. 4. At this time of year we are scouting leaves for active infections of downy mildew and powdery mildew (new infections are unlikely to form from this point forward), and examining clusters for botrytis and sour rot infections. The incidence of disease symptoms at the Berrien County scouting sites remains low. No black rot infections were seen on Concord clusters, but downy mildew lesions were seen on 10 percent of leaves. In Vignoles, old infections of phomopsis were seen on 10 percent of clusters. Single black rot-infected berries were seen on 6 percent of clusters, but no further infection is expected. Downy mildew or powdery mildew were not observed on leaves or clusters in Vignoles, but botrytis (8 percent of clusters infected) and sour rot symptoms (36 percent of clusters infected) are increasing. Growers should continue monitoring leaves for downy and powdery mildew and, especially in tight clustered varieties, growers should check clusters for developing symptoms of botrytis and sour rot infections. Treatment may be necessary to control these late-season diseases to ensure the canopy remains healthy and fruit quality is maintained.

Van Buren County farms visited Friday, Sept. 4

Niagara are ripening, clusters are continuing to tighten and harvest is expected to begin around Sept. 21. Similarly, Chancellor is well into veraison, and harvest should begin around Oct. 1.

The number of grape berry moth males caught in traps has decreased over the past two weeks and ranged from zero to 20 moths per trap. This trend is similar to that in Berrien County and shows the third flight is ending in this region. Grape berry moth damage in these vineyards has remained steady over the past two weeks and feeding damage by third generation larvae ranged from 60 to 96 percent of clusters with some level of damage. The incidence of damage in these high pressure vineyards is highest at vineyard borders, but the severity of feeding remains low and many of the damaged clusters contain only one or two damaged berries. At this point in the year, we are not expecting a fourth generation of grape berry moth. However, depending on the length of the third generation and the level of grape berry moth pressure, an additional insecticide application may be required in some vineyards before harvest.

Potato leafhoppers and Eastern grape leafhoppers were not seen during scouting on Sept. 4, and no Japanese beetles were observed. However, growers should continue scouting for these pests, as well as the harvest-time pests mentioned above, from now until harvest.

Diseases have been well-managed in the vineyards we scout in Van Buren County. Downy mildew and powdery mildew symptoms were absent from clusters in Niagara or Chancellor, even though these varieties are susceptible to these pathogens. Downy mildew leaf lesions, or “oil spots,” were seen in the Niagara vineyards, and the incidence of infected leaves has not increased over the past two weeks. Approximately 16 percent of leaves had downy mildew symptoms, but most importantly, the disease has not moved onto the fruit. Black rot lesions were seen on 12 percent of clusters in Niagara. In Chancellor vineyards, symptoms of black rot (5 percent infected clusters), phomopsis (4 percent infected clusters) and botrytis (4 percent of cluster with symptoms) were seen on fruit. Growers and scouts should still be checking vineyard canopies for active infections of downy mildew and powdery mildew on leaves, and botrytis and sour rot infections on clusters. It will be important to ensure these pathogens do not increase between now and harvest, so additional fungicide applications may be needed before season’s end.

Enviro-weather growing degree day summary for 2015 (GDD50 from March 1)


Sept. 7

Sept. 14 (projected)

Berrien Springs






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


Wild grape bloom

Current GDD after wild grape bloom (as of Aug. 24)

Fourth generation egglaying (2,430 GDD after wild grape bloom)


May 26


Low risk of occurrence

Van Buren (Lawton)

May 28


Low risk of occurrence

Van Buren (Mattawan)

May 29


Low risk of occurrence

Allegan (Fennville)

June 3


Low risk of occurrence

Please consult the Michigan Fruit Management Guide (E0154) for management options for insects, diseases and weed.

There will be one more grape scouting report for the 2015 season, the preharvest wrap up on Sept. 22.

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

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