Early season disease management in Vermont vineyards

May 13, 2015

by Terence Bradshaw

With bud burst in cooler sites and grape shoots ranging from 1-3″ in the Champlain Valley is the time begin thinking about disease management. I’ll put it simply: the next four fungicide applications, combined with good vineyard sanitation, will ‘set the stage’ for your vineyard in 2015 as far as diseases are concerned.

Disease Management at the 3-5 Inch Shoot Growth Stage – The following was written by Dr. Wayne Wilcox of Cornell University and appeared in the article “Grape Disease Control, 2013”: [Note:   Ph = Phomopsis; PM=
powdery mildew; BR= black rot; DM= downy mildew]

“3 – to 5-INCH SHOOT GROWTH. A critical time to control Ph rachis infections if it’s raining or likely to be soon, especially in blocks with any history of the disease. Early is better than late if it looks like some rain is setting in. Late is much better than nothing if those are the only two options , i.e., you’re past this stage, haven’t gotten anything on, and wonder whether it’s too late . This spray can provide significant benefit against fruit infections as well, since many of them originate from movement into the berries from infected rachises and berry stems. Also an important time to control basal shoot infections, since this is where the fungus will establish itself for the future if infected tissue is retained in canes, spurs, or pruning stubs.

Now is the time to start thinking about control of PM on vinifera varieties if temperatures remain above 50 °F for long stretches of the day… This spray is much more likely to be important in vineyards that had significant PM last year (we’re talking late season foliar disease more than fruit infections here) than in those that were “clean ” into the fall; however, it may be beneficial even in relatively clean blocks of highly susceptible cultivars, which tend to be relatively valuable as well… If already spraying for Ph, most growers of highly susceptible (and valuable) varieties include something for PM while they’re at it. I would too.

In NY, spending extra money for BR control is almost never justified this early unless you’re trying to clean up a severe problem block AND weather is wet and reasonably warm. In general, the farther south you go, the more important early sprays can become. Still too early for DM.

Disease Management options for the 3-5 Inch Shoot Growth stage are listed on pages 55-58 of the printed version of the 2015 New York and Pennsylvania Pest Management Guidelines for Grapes.

Unless you have had issues with anthracnose or extensive black rot on your vineyard, an application of a protectant fungicide such as mancozeb or captan should be sufficient at this time.

Terence Bradshaw, UVM Tree Fruit and Viticulture Specialist