IN YOUR ORCHARD
TIME TO CONSIDER Red leaf blotch is a disease almond growers should take seriously. It can have a multi-year impact on your crop. As with all things farming though, growers are adaptable. We understand the life cycle of this disease and have the tools to control it. The final step is to act. Don’t shrug it off like I did last year! It’s here and it will remain here for the foreseeable future. Last year, while walking through our family’s orchards with my dad and brother, I mentioned a new disease that had recently appeared in California almonds. “It’s called red leaf blotch,” I said, “but it’s only been spotted in a few areas.” We all shrugged it off. With a solid fungicide program in place, it seemed like just another new name making the rounds. Then came this year. By late May, I began noticing distinct discoloration in orchards across Stanislaus and Merced counties. One day, my dad called and said, “Hey, you know that new disease? We’ve got it. What can we do about it?” It was red leaf blotch and it was spreading fast throughout the region. This isn’t a disease we can afford to ignore. It demands a focused, proactive management plan. Red leaf blotch was first detected in a few counties last spring. Experts believe the pathogen was introduced into California via infected plant material. A local PCA (Pest Control Advisor) pointed out a key difference between this year and last year. Last year, the question was “Is the disease present in the orchard?” This year, it’s “To what extent is the orchard infected?” Severity varies, but orchards with high infection levels this year were, typically, affected last year as well. Red leaf blotch follows a single infection cycle. Active spores are present around petal fall, just as young leaves are emerging. Rain during this period splashes spores onto the leaves, initiating infection. Symptoms appear 35–40 days later.
Figure 1: Red leaf blotch in Merced County. Photo credit: Trent Voss
The early signs include small, yellowish spots that enlarge and change color from orange to reddish-brown. As blotches grow, leaves begin to curl and eventually drop prematurely. This defoliation reduces photosynthesis, impacting the current crop and significantly affecting next year’s yield due to lower carbohydrate reserves in the trees.
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ALMOND FACTS
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