What is in this article?:
- Grape powdery mildew survey a Farm Press, UC Davis effort
- Top grape growers, PCAs
- Grape growers and PCAs use the Gubler-Thomas Powdery Mildew Index (PMI) for making decisions about powdery mildew management.
Top grape growers, PCAs
“The powdery mildew CEU course is one of the most popular ones because it was developed with the guidance of Dr. Gubler, who is recognized worldwide as a leading authority on powdery mildew management,” said Cline.
The survey was emailed to those who identified grapes as their primary crop.
The majority of the 112 respondents were PCAs (49 percent) and individual vineyard owners (36 percent). Almost 30 percent of individual vineyard owners were also PCAs. Average experience working with grapes was 16 years with 30 percent of the respondents reporting between 20 and 25 years of experience.
Just over 80 percent of the respondents reported managing up to 2,000 acres with a few respondents reporting larger operations of 10,000 acres or more.
These demographics from the survey were very enlightening to the Penton Ag CEU team. “The growers and PCAs surveyed from the CEU database represent the largest grape growers in the state,” said Cline. “This indicates to us that the pentonag.com portal is utilized by the top grape PCAs and grape growers in California.”
There are currently 20 CEU courses offered at pentonag.com. All are accredited by the California Department of Pesticide Regulation for all state licensees, including county private applicator certificate holders.
The survey results showed that 50 percent of the survey participants managed more than one vineyard.
Growers said they evaluated the risk of powdery mildew mostly on weather conditions and their own experience (45 percent). About a third relied heavily on the Powdery Mildew Index and PCA recommendations.
Just over 50 percent reported receiving recommendations from an external PCA. The majority of those recommendations (57 percent) came from PCAs working for their agricultural supplier. Almost 20 percent came from in-house PCAs and 16 percent came from independent PCAs.
In response to increased risk of powdery mildew, most growers frequently adjusted their treatment timing. About a quarter of them also reported switching to different chemicals and a slightly smaller group (18 percent) reported regularly adjusting treatment dosages.
The PMI was quickly adopted by those who tried it. Less than 10 percent of the growers reported discontinuing its use once they used it.
The main reason PMI is used is to reduce the probability of powdery mildew outbreaks. 55 percent reported it as “extremely important.”
The second and third most important motivations were reducing chemicals costs (20 percent) and reducing fungicide residue on berries (20 percent).
Raisin growers were the most concerned about reducing costs, and the group that placed the most importance on PMI use across all four areas of concern.
The PMI model is detailed in the powdery mildew course on the pentonag.com CEU portal. The course is offered free by Farm Press.
The UC IPM website on-site weather stations are the two primary sources for PMI data. Most respondents are located in Fresno County with others coming from San Joaquin, San Luis Obispo and Sonoma counties.
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