Vineyard IPM scouting report for June 2, 2014

Southwest Michigan growers should get ready to start their grape berry moth model and plan for final pre-bloom fungicides. Wild grape is blooming over much of the region.

Two common wild grape species in Michigan. On the left is summer grape while on the right is riverbank grape. Be sure to use the timing of bloom riverbank grapes for assisting with vineyard decisions.

Two common wild grape species in Michigan. On the left is summer grape while on the right is riverbank grape. Be sure to use the timing of bloom riverbank grapes for assisting with vineyard decisions.

Wild grape is at or past full bloom – 50 percent of the flowers are open on 50 percent of the clusters – in Berrien and Van Buren counties, and this means several very important things for vineyard integrated pest management (IPM). We must first make sure that we are talking about the correct species of wild grape, the riverbank grape, Vitis riparia. This common species of wild grape has leaves that are shiny green underneath with very few, if any, hairs. There is another common species, summer grape, Vitis aestivalis, that has leaves that appear white or gray on the underside because they are covered in hairs (see photo).

These two species bloom at least two weeks apart, so Michigan State University Extension experts say it is critical to look at the right species to help with your vineyard management decisions. Another clue to help know when to look for wild grape bloom is that the correct species to look for, the riverbank grape, blooms at about the same time as black locust, which is a very common tree with very noticeable white flowers. See the Michigan Grape and Wine Newsletter from May 15, 2012, for more about this tree.

In many varieties of cultivated grapes, we can expect bloom in the vineyard about a week after wild grape bloom, so this signals that the final pre-bloom insecticides will need to be applied soon. Another very important thing about wild grape bloom is that it can be used to predict when the middle- and late-season generations of grape berry moth are expected to start laying eggs on clusters and when the clusters need to be protected. The MSU Enviro-weather Grape Berry Moth Model  can help you decide when it is best to apply insecticides to protect from this pest. However, you will need to know the date of wild grape bloom around vineyards in your area so that the date can be entered into the model to predict egglaying.

Ideally, it is best to assess the wild grape on your own farm to make the best predictions and to write this down on a calendar or notebook. Our recent observations on farms that are part of the MSU Vineyard IPM Project put the biofix of full bloom to be May 29 in Berrien County and June 2 in Van Buren County.

Growing degree day summary (GDD50 from March 1)

The recent warm weather and accumulating GDDs have increased the rate of development of vines and some insects. We are now only about 25 GDD behind the 2013 spring.

Enviro-weather site

June 2

June 8 (projected)

Berrien Springs

505

573

Lawton

494

580

Berrien County farms, visited Monday, June 2

Concord bloom is expected to occur in the next week and Vignoles are now at 8- to 12-inch shoots. A few flea beetle larvae were seen feeding on leaves, but damage is still low where we are scouting. Low activity of the leaf feeding stage of phylloxera and some young galls formed by the grape tumid gallmaker were found in some vineyards and in wild grapevines in adjacent woodlots. Scouts, growers and crop consultants should be on the lookout for symptoms of these pests, especially in vineyards with a history of infestation.

The number of grape berry moth males that have been caught in pheromone traps has increased steadily at all sites and ranged from four to 131 moths per trap. We are likely at or nearing the peak of male flight and we expect females to become active in vineyards in the next week to 10 days. No action for control of this pest is necessary at this time. Very little damage results from this first generation of grape berry moth. In vineyards where there is low to moderate infestation at harvest, growers should consider not using insecticide for this generation. We would recommend concentrating control efforts on the middle- and late-season grape berry moth generations, and the timing for these can be based on the degree day model mentioned above.

Growers are preparing to put a final pre-bloom fungicide cover sprays targeting phomopsis, powdery mildew, downy mildew, black rot and anthracnose. No disease symptoms were seen at these vineyards during scouting on June 2.

Van Buren County farms, visited Monday, June 2

Niagara was at pre-bloom and Chancellor was at 16- to 18-inch shoots. Grape berry moth males were captured at all the farms we visited in Van Buren County and the number caught in traps remains high, ranging from 18 to 121. This suggests we are at or approaching the peak of male flight, but no action for control of this pest is necessary at this time (see above). As in Berrien County, growers are preparing for the final fungicide application before bloom. Disease symptoms were not seen at these vineyards during scouting on June 2.

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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