UCONN IPM: Integrated Pest Management:UConn Grape IPM Message

Vines have progressed into the 1-5 inch shoot stage and many are even in the 8-12 inch stage. This means it’s time to monitor and control Phomopsis cane and leaf spot, downy mildew, powdery mildew, and black rot.

Powdery mildew: Bark and leaves that were heavily infested with powdery mildew in 2008 have been stored outdoors at several sites in CT, MA, and RI. Each week since May 1, samples have been tested for maturity of the fungal inoculum. As of May 20, none of the spores were mature, but this may change fast. The weather has been conducive for heavy powdery mildew ascospore infection for half the days of May at almost every southern New England vineyard (to see the weather data and model outputs, check-out the next issue of New England Grape Notes or go to the CT Agricultural Experiment Station website, http://www.ct.gov/caes/ and look for Remote Weather Data). As soon as the spores are mature, they will be released during rains. Subsequent infections are favored by high humidity and temperatures between 68 and 81 ^o F. Last year, the ascospores reached maturity during the last weekend of May. This year we would expect maturity a little sooner.

Other diseases: Looking over the other disease model predictions for Phomopsis cane and leaf spot, black rot, and downy mildew, it is striking to see how uniform the results are among sites. There was risk of infection for black rot for most of the days in the first and third weeks of May for all sites. The same periods had weather conducive to downy and powdery mildew infection, although it was a bit early for those at that time. When we got to warm dry weather on 5/18, all the disease risk fell way off. The Phompsis model projects the estimated lesions per leaf of this disease. Infectivity was moderate to high in CT for much of early and mid-May. More northern sites, like Deerfield, MA had fewer days of high infectivity.

As soon as the weather turns wet again, all of these diseases could take-off. It makes sense to follow a standard fungicide program. You may have made one or two applications already, based on the info in New England Grape Notes or other sources. A logical choice at this time would be to apply a mancozeb spray with either rubigan or sovran or nova. The mancozeb will cover Phomopsis, black rot and downy mildew while the rubigan or sovran or nova will cover powdery mildew. I would follow up in 7-10 days depending on the weather. It is best to time the spray for before a wetting period if you can.

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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Disease Management