As 2011 continues to be a challenging powdery mildew year, vineyards may need more later-season sprays than anticipated to keep the disease at bay. “This spring’s cooler temperatures slowed the disease’s progression,” says Larry Bettiga,viticulture farm advisor for Monterey County, “but now temperatures are holding steady at cooler-than-normal levels for this time of year—between 68oF and 86oF. Because of that, powdery mildew infections are spiking since conditions are right for ascospores release.”
Bettiga believes enabling good spray coverage, reacting quickly to weather changes, and keeping spray plans flexible are key to controlling powdery mildew in cooler seasons.
Open Closed Canopies
As maturing canopies begin closing, spray applications may not fully penetrate, leaving areas susceptible to powdery mildew. “Even a small infection in a young canopy can become a big problem once it’s enclosed in a dark canopy and the weather warms up,” says Bettiga. Opening up dense canopies lets in light and heat, reducing optimal conditions for powdery mildew and bunch rot organisms while helping ensure thorough spray coverage.
React to Weather Shifts
Quickly translating how a weather change will affect powdery mildew pressure in a vineyard can mean the difference between prevention and outbreak. The Powdery Mildew Risk Assessment Index created by UC-Davis helps identify periods with higher risk of ascospore infections so timely preventive sprays can be made before outbreaks occur. Bettiga discusses the Index in more detail here.
Stay Ahead with Sprays
Don’t let your guard down when it comes to getting product out in the vineyard, cautions Bettiga. “Just because you can’t see the disease doesn’t mean it isn’t there. Once you see it, the infection has already taken hold,” he says.
Maintaining a preventive spray schedule is important because many powdery mildew products are preventive and cannot eradicate existing infections. “Preventing powdery mildew infections in the first place is less costly and time consuming than trying to eradicate existing infections,” reminds Bettiga. If infections do occur, Bettiga recommends using an eradicant to clean up any disease before going back out with a preventive product.
Bettiga encourages PCAs to be flexible when it comes to selecting materials and creating spray schedules. Using the Powdery Mildew Risk Assessment Index and other tools can help in making informed decisions about which products and application intervals will work best in specific situations. “The more flexible you are in matching products and applications to weather and pressure shifts, the more effective your powdery mildew control will be,” says Bettiga.
Be Smart About DMIs
DMI fungicides are a popular choice for additional sprays, but Bettiga cautions PCAs to be aware of the potential for resistance. “We’ve had DMI resistance issues in the past,” says Bettiga. “Older DMI products tend to have more potential for resistance issues, but many newer DMIs have good activity and can work if used correctly.” Listen to more of Bettiga’s advice on using DMIs here.
One option is Viticure fungicide from Chemtura AgroSolutions. “Viticure is a good choice for the DMI slot in the rotation because it offers different activity than other DMIs, providing powdery mildew control while reducing the potential for DMI resistance,” says Henry Wu, technical sales support representative for Chemtura AgroSolutions.
As a systemic DMI fungicide with different chemistry than the triazole chemistry found in most other DMIs, Viticure provides protective and curative control of powdery mildew. In addition, Viticure is also labeled for suppression of black rot and Botrytis bunch rot.