Vineyard IPM scouting report for July 15, 2014

Wet weather is fueling higher disease pressure and grape berry moth second generation is going strong, but where are the other insect pests?

In our scouting in southwest Michigan vineyards over the past two weeks, we have seen an increase in the incidence of grape diseases including downy mildew, black rot, phomopsis and powdery mildew. There also has been an increase in grape berry moth damage in clusters on vines that are adjacent to wooded areas. Captures of male grape berry moth have remained steady over the past two weeks as the second generation continues. We can expect grape berry moth egglaying to continue from now until harvest, although cooler weather should slow egglaying and reduce the rate of development of eggs and larvae in clusters for the time being.

Growers and vineyard managers with a history of berry moth infestation and have not treated for this pest yet may need to apply insecticides to clusters at this time. Egg hatch by this pest is well underway in southwest Michigan, and the overall efficacy of Intrepid, Altacor, Belt, Dipel or other products that are active on eggs and young larvae may be reduced. Contact insecticides such as Imidan, Baythroid, Bifenthrin, Delegate and others will be better options to apply now to target egg hatch. Consult the “2014 Michigan Fruit Management Guide” (E-154) from Michigan State University Extension for a more comprehensive list of insect and disease control options.

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

County

Date of wild grape bloom

Start of second generation egglaying

Current GDD after wild grape bloom as of July 14

Berrien

May 29

July 4

1,052

Van Buren

June 2

July 9

957

Very few other pest insects were seen in the vineyards we scout in Berrien and Van Buren counties. Eastern grape leafhoppers and potato leafhoppers were at very low levels, and still well below economic thresholds. A few Japanese beetles were observed during scouting, but only very light feeding damage was seen on leaves. Control of this pest is not needed at this time as the number of beetles observed is still low and the vines have abundant leaf area to ripen the potential crop. Although wine grape varieties are more adversely affected by Japanese beetle feeding than are juice grape varieties, the beetles often feed at the top of the canopy, and on a vertical trellis system their feeding typically does little to reduce the capacity to ripen the crop. This will be particularly true this season with the lighter crop load in many vineyards. Growers of susceptible vinifera and hybrid varieties should still scout regularly to detect possible build up of Japanese beetle populations and plan to treat if canopy protection is needed.

MSU Enviro-weather degree day summary (GDD50 from March 1)

Site

July 14

July 20 (projected)

Berrien Springs

1,302

1,376

Lawton

1,268

1,364

Berrien county farms scouted Monday, July 14

Concord is well past berry touch and the berries are sizing well. Vignoles are now at berry touch and many clusters are tightening rapidly. Eastern grape leafhoppers and potato leafhoppers were not seen in the vineyards we scouted. Japanese beetle numbers have increased over the past two weeks, but numbers are low and there is no need to treat for this pest at this time (see above). Low numbers of spotted wing Drosophila have been caught in monitoring traps in vineyards, but as there is no ripe fruit yet, we do not expect any infestation in vineyards at this time.

The second flight of grape berry moth males has remained low and steady over the last week, and the number of moths caught in pheromone traps ranged from zero to 17. Second generation larvae can be found in clusters in vineyard hot spots, and in some border areas, 30 to 40 percent of the clusters have evidence of active berry moth feeding (webbing and frass). In vineyard interiors, grape berry moth damage ranged from 0 to 6 percent of the clusters with grape berry moth feeding damage. Border treatments can be considered at this time to prevent further increase in infestation.

Disease incidence has increased over the past two weeks. In Vignoles, phomopsis leaf lesions were fairly widespread with about 25 percent of the leaves showing symptoms during scouting on July 14, but no evidence of any other leaf, shoot or cluster diseases were seen. Low levels of phomopsis leaf lesions were seen in Concords (7 percent leaves with symptoms), and phomopsis was also seen on the rachis in 4% of the clusters.

Van Buren County farms scouted Monday, July 14

On July 14, Niagara and Chancellor clusters were tightening. Consistent low captures of grape berry moth males show the second generation flight is progressing, and the level of feeding by larvae in clusters is similar to what was seen in Berrien County (30-40 percent clusters infested on borders and 0 to 6 percent in vineyard interiors). As was seen in Berrien County, very low levels of grape leafhoppers and potato leafhoppers were present in the vineyards we scouted. Japanese beetle numbers are increasing, but populations are not large enough to warrant treatment.

We did detect the presence of phomopsis (9 percent of leaves), black rot (3 percent of clusters), downy mildew (2 percent of leaves and 3 percent of clusters) and powdery mildew (1 percent of leaves and 1 percent of clusters) this week on Chancellor. In the Niagara vineyards we monitor as part of this project, we recorded phomopsis leaf lesions on 4 percent of the leaves, and black rot symptoms were detected on 7 percent of the clusters.

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.

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