VT pathologist Nita offers guidelines for grape growers
MONROE TOWNSHIP, N.J. — Dr. Mizuho Nita, an Extension specialist in grape pathology at Virginia Tech, offered up pest control suggestions when it comes to growing grapes at the 20th annual “Grape Expectations” conference at Forsgate Country Club in March.
Nita is an Ohio State graduate who has been doing research at Virginia Tech for the last decade.
Dr. Nita showed slides of powdery mildew, black rot, ripe rot, downy mildew and various other afflictions that vineyard owners throughout the Mid-Atlantic must deal with.
Some fungicides become less effective over time, and some forms of fungus-based diseases become fungicide resistant, he said and why and how this happens is the subject of ongoing research.
Nita said that among fungicides he and his team tested, Captan and Mancozeb seemed most effective in combatting a host of fungal diseases.
“Make sure you do careful, proper rotation in your spraying and make sure the product number starts with an M, not a number,” he cautioned regarding spraying fungicides for powdery and downy mildew.
“Last year we had a dry spell for a couple of months in Virginia, so it was not a typical year for powdery mildew,” Nita said.
If there is rain in the forecast, grape growers should make every effort to spray before the rain event happens, not after it, he stressed.
Dr. Nita’s research into combatting powdery mildew, downy mildew, ripe rot, black rot and botrytis or gray mold, used a variety of fungicides, including, but not limited to: Captan Gold, Mancozeb, Tepsin M, Abound, Ph.D., Prophyt, Aprova, Endura, and Luna Privilege.
“In my trials I was spraying the same material four times in a row,” Nita said. “I’m not recommending that you guys do that, this is to test if this particular chemical works or not, and it often says on the label you can spray only three times a year or twice a season. It depends on the product,” so follow the label instructions, he stressed.
Nita displayed more results from studies undertaken at Virginia Tech research farms in 2016 and said the goal was to find something effective to combat powdery mildew.
“In 2017, we didn’t have much powdery mildew growing, we had a lot of rain early in season and it was really cold, and then we had a dry spell for a couple of weeks but not enough rain to get much powdery mildew sporing,” Nita said.
With black rot, Mancozeb appears to be able to work effectively for now, Nita said.
“It you have a mixture and a couple of different modes of action, it can actually prolong the life of the products you’ve applied,” Nita said. “When we talk about downy mildew, it has a little bit different application time. We try to spray it over 10 to 12 days, and sometimes depending on weather conditions we have to stretch into a 14-day interval.”
He was critical of the fungicide manufacturers, noting not many new products have been introduced in recent years.
“If you take a close look at mode of action, it’s nothing new; they change the formulation they have a different way to attack the target site, but the actual mechanisms to stunt the growth or to kill the pathogen is the same,” Nita said, and added, “you really have to use a number of applications, especially if it’s a newer product. When you look at the code that is supposed to be on the label, if the number starts with a number, 3 or 37 or 14, it means that particular product has either medium or high risk of having an issue with resistance,” Nita said.
Nita recommended growers apply a product up to twice a season, nothing beyond that.
“Try to mix with a product where the product number begins with M for M4 for Mancozeb, then you can spray more than a couple of times, but make sure you have a rotation. Unfortunately, each species has different profiles and so is their sensitivity to fungicides as well.”
More information on Nita’s ongoing research to combat grape vine afflictions in his online blog, Virginia Grapes Disease Update, at http://grapepathology.blogspot.com.
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