A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines
Almond hulls split in a healthy orchard in Ripon. Researchers, growers and pest control advisors are on the watch for red leaf blotch disease after its recent discovery in some California almond orchards.
First finding of red leaf blotch in California almonds By Vicky Boyd
lesion that goes across the leaf area. I’m not a plant pathologist, but it looked a little off to me, especially with the color.” He contacted Trouillas and followed up with the consultant to visit the orchard for a closer look. Trouillas’ team also collected samples, which were confirmed as red leaf blotch by his lab, CDFA and the U.S. Department of Agriculture. Zuber said he has since visited a few other orchards in Merced County that had suspi- cious yellow and orange spots, but they have not yet been confirmed as red leaf blotch. In the original orchard, he said he didn’t see any defoliation. In subsequent ones, Zuber said he saw some but not widespread defoliation caused by what he assumed was red leaf blotch. As word of the disease spread and telltale reddish-brown leaf spots became more ad- vanced in June and July, northern San Joaquin Valley farm advisors began to receive an uptick in calls about suspicious leaf spots. So far, the disease has been found in Madera, Merced, San Joaquin and Stanislaus counties, suggesting it is “somewhat widespread” in the northern San Joaquin Valley, Trouillas said. Suspicious symptoms also have been found but not yet confirmed in a Fresno County orchard. See BLOTCH, Page 7
University of California plant pathologists have confirmed red leaf blotch disease in almonds for the first time in the state, prompting calls for farmers and pest control advisors to keep their eyes peeled. “The first step is to reach out to UC Extension so the disease can be confirmed—that’s the most important step,” said Florent Trouillas, UC Cooperative Extension fruit and nut crop pathology specialist. “From the disease management perspective for this year, it’s too late. No fungicide is effective once the symptoms are visible, so the whole management strategy needs to be initiated next year in the spring.” Contacting UCCE farm advisors about suspicious leaf spots also will help the almond industry understand how widespread the fungal disease is, he said. In addition, the infor- mation will assist the California Department of Food and Agriculture determine a specific pest rating. Because of red leaf blotch’s prevalence, Trouillas said it’s likely here to stay. The disease first surfaced in California in May when UC orchard crops advisor Cameron Zuber contacted Trouillas about unusual leaf symptoms in an almond orchard straddling the Merced-Madera county line. Infected leaves on the nonpareil, Monterey and Fritz varieties had yellow spots with orange to dark red-brown centers. Zuber said a consultant had texted him photos of unknown leaf symptoms on May 29. “When I first saw it, I was a little concerned,” he said. “It’s very odd to get this large a
6 Ag Alert August 14, 2024
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