PHOTO COURTESY OF CORNELL UNIVERSITY
For Washington grape growers who had a bunch rot problem in 2010, efforts to get rid of any carryover crop are worthwhile, says a New York plant pathologist. Growers should also be prepared to spray a botrytis-specific fungicide during bloom, if weather conditions are favorable for the disease.
If growers can throw leftover material during dormant pruning into the row middle to be disked, it will be helpful, said Cornell University’s Dr. Wayne Wilcox. “If you can take care of it without standing on your head and spending a lot of money, it’s a good thing to do.”
To growers who had a problem with Botrytis cinerea (bunch rot) last year, he said: “Realize that you already have the inoculant. Now, all you need is the right environment. If it’s as wet this year as it was in 2010, your disease will be worse.”
While vineyard sanitation is a worthy goal, he believes that one or two well-timed fungicides that might not have been applied otherwise are more cost effective.
Wilcox suggested Washington growers concerned with botrytis use the following strategy in 2011:
- Spray during bloom. Unless it’s bone dry before and after bloom, spray during bloom with a product that will be effective against both botrytis and powdery mildew.
- Monitor latent infections for presence of disease. Monitor for infection by picking bunches when berries are the size of BB pellets. Put them in a Ziploc bag, and freeze. Let thaw in bag with moistened paper towel for two days and watch for fuzzy growth.
- Monitor weather during veraison. If rain is forecast, it might be wise to invest in a $30 to $40 per acre
- fungicide spray to provide botrytis control.
- Apply botrytis-specific product if postveraison/preharvest control is needed. Vanguard, Elevate, and Rovral (if disease resistance is not established) have been effective in New York efficacy trials.