Vineyard IPM scouting report for June 16, 2014

Scout vineyards for post-bloom insect activity and diseases as now is the time to protect vines from post-bloom diseases.

Posted on June 17, 2014 by Keith Mason, Michigan State University Extension, Department of Entomology; Annemiek Schilder, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences; and Rufus Isaacs, Michigan State University Extension, Department of Entomology

Most varieties of cultivated grapes are finishing bloom this week, with a few wine grape varieties still in full bloom. Additionally, there are vineyards with winter injury where there are many buds on secondary shoots that have yet to bloom. We are starting to see some early infestation by grape berry moth larvae in clusters, and a few eastern grape leafhoppers on the undersides of leaves. However, infestation levels are very low in the vineyards we scouted, and would be considered below economic thresholds. We are still seeing small numbers of rose chafer in the vineyards we scout in Berrien and Van Buren counties. We have not observed any phomopsis, black rot, downy mildew or powdery mildew on clusters, but some early signs of phomopsis leaf lesions are now visible in the vineyards we are monitoring.

Michigan State University Enviro-weather growing degree day (GDD) base 50 summary from March 1

Warm days have fueled plant and insect development, and we are now only about 5 to 10 GDDs behind spring 2013, so this is shaping up to be a more “normal” season. This is also reflected in the progression of the MSU Enviro-weather grape berry moth GDD model, as we are now about half way to the 810 GDD target for the start of the second generation of this pest when cluster protection is critical. The current estimate is that second generation egglaying would begin after July 4.

Berrien County farms scouted Monday, June 16

Concord bloom is finishing and Vignoles, which have mostly secondary clusters, are now in full bloom. The leaf feeding stage of phylloxera and some young galls formed by the grape tumid gallmaker have become more evident in some vineyards and in wild grapevines in adjacent woodlots. Michigan State University Extension advises scouts, growers and crop consultants to be on the lookout for symptoms of these pests, especially in vineyards with a history of infestation.

Rose chafers are also present in vineyards, and as these beetles feed on developing clusters, they can greatly reduce yield if left unchecked.

The number of grape berry moth males that have been caught in pheromone traps is still high at most sites, and ranged from three to 97 per trap. The number of moths per trap has decreased over the last couple of weeks at the sites we scouted, so we are likely past the peak of male flight which usually overlaps with the start of egglaying. Larvae can be seen on clusters in vineyard hot spots with a history of grape berry moth infestation. These hotspots are usually located near woodlots that contain wild grapes.

In most situations, very little damage results from this first generation of grape berry moth. Vineyards can be scouted to check for infestation in clusters. If less than 5 percent of the clusters have grape berry moth infestation, one should consider omitting insecticide from the post-bloom application, and using the MSU Enviro-weather grape berry moth model to help concentrate control efforts on the middle and late season grape berry moth generations. Some vineyards may still require post-bloom insecticides for control of rose chafers or other leaf-feeding pests.

Disease symptoms were still at very low levels at the monitored vineyards during scouting on June 16.
With rain forecast over the next few days, growers are preparing to apply a post-bloom fungicide cover spray to protect the vines from phomopsis, powdery mildew and downy mildew, black rot and anthracnose.

Van Buren County farms scouted Monday, June 16

On June 16, Niagara was at post-bloom and Chancellor was at full bloom. Grape berry moth males were captured in traps at all farms we visited in Van Buren County and the number caught in traps remains high, ranging from four to 84. Similar to observations from Berrien County, grape berry moth larvae, rose chafers and very low levels of grape leafhoppers are present in the vineyards we scouted. As in Berrien County, no disease symptoms were seen on clusters, and very low levels of early phomopsis leaf lesions were seen on Chancellor.

Growers are preparing for post-bloom fungicide applications. Our grower cooperators on this IPM project will include insecticide in their post-bloom application as their vineyards have a history of high grape berry moth infestation, along with low levels of other pests such as rose chafers and leafhoppers observed during scouting on June 16.

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.

This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).