By the Chemtura AgroSolutions team of experts
Rising temperatures mean conditions are nearly perfect for an explosion of powdery mildew in vineyards.
“I’m finding areas with the disease in the beginning stages,” says Nathan Ostly, PCA with Kerman Ag Resources in Madera, Calif. “Temperatures are right for it to take off.”
According to the University of California’s grape powdery mildew risk assessment index (RAI) website this week, powdery mildew disease pressure is high at nearly every reporting station.
The RAI is derived from this formula:
After you find powdery mildew, an epidemic will begin when there are three consecutive days with six or more continuous hours of temperatures between 70 degrees and 85 degrees F as measured in the vine canopy.
1. Starting with the index at 0 on the first day, add 20 points for each day with six or more continuous hours of temperatures between 70 degrees F and 85 degrees F.
2. Until the index reaches 60, if a day has fewer than 6 continuous hours of temperatures between 70 degrees F and 85 degrees F, reset the index to 0 and continue to monitor.
3. If the index reaches 60, an epidemic is under way. Begin using the spray-timing phase of the index.
The current RAI ranges from 60 to 100, with many stations ranked at 90 or 100, meaning properly implementing powdery mildew management strategies is critical.
“Most vineyards are finishing up their second sprays. With powdery mildew pressure being what it is and a lot of irrigation taking place, the timing is good to apply Viticure® fungicide,” says Ostly.
Viticure is a systemic sterol inhibitor fungicide that’s labeled for protective and curative control of powdery mildew. It works by inhibiting development of the target organism’s cell walls, without which the organism cannot survive. Viticure can be applied in rotation throughout the season and also suppresses black rot and Botrytis bunch rot.
Be sure to visit with your PCA or Chemtura AgroSolutions representative for additional ways to ensure a successful season:
• Mike Ansolabehere, Southern San Joaquin Valley: (661) 304-3023 or email Mike.Ansolabehere@Chemtura.com
• Matt Loftus, Central San Joaquin Valley: (559) 960-1112 or email Matthew.Loftus@Chemtura.com
• Eric Leer, North Central California: (209) 531-6478 or email Eric.Leer@Chemtura.com