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Posts Tagged: pest
Almond crop yields threatened by disease new to California
Detection of fungus causing red leaf blotch spurs call for grower vigilance
Symptoms of red leaf blotch (RLB), a plant disease caused by the fungus Polystigma amygdalinum, have been observed for the first time in California across the Northern San Joaquin Valley.
Molecular DNA testing by the laboratory of Florent Trouillas, University of California Cooperative Extension fruit and nut crop pathology specialist, has detected P. amygdalinum. Pest identification was confirmed by the California Department of Food and Agriculture and U.S. Department of Agriculture.
The disease, named for the characteristic orange-to-dark red blotches that appear on infected leaves, is typically nonlethal for trees but has been a long-standing problem for almond-growing regions across the Mediterranean. Causing trees to lose their leaves prematurely, the fungal pathogen can significantly diminish crop yields in the current year and the next.
“It is one of the most severe diseases of almonds for Spain and the Middle East,” said Trouillas, an associate professor in the UC Davis Department of Plant Pathology. He recently co-authored an explanatory article on the UCCE San Joaquin Valley Trees and Vines blog.
With symptomatic trees seen in multiple orchards across Madera, Merced, San Joaquin and Stanislaus counties, Trouillas said RLB is already “somewhat widespread.”
“From the first observations so far, it seems like it affects some of the most-planted cultivars, like Nonpareil and Monterey,” he added. “We've observed it in a diversity of cultivars already.”
UC Cooperative Extension specialist urges taking preventive measures
According to Trouillas, RLB caused by P. amygdalinum is “highly specific” to almond trees, and generally only affects their leaves. Infection typically happens at petal fall, when small leaflets are first emerging and most susceptible to disease. After the pathogen's latent period of about 35 to 40 days, the first symptoms appear – small, pale-yellow spots on both sides of the leaves.
Those blotches become yellow-orange and then reddish-brown in the advanced stages of the disease during June and July. Now, with RLB symptoms becoming more prominent, Trouillas and UC Cooperative Extension advisors across the Central Valley have seen an uptick in calls.
“PCAs [pest control advisers] have been confused because they've never seen anything like this,” said Trouillas, noting that the yellow-orange-red blotches are symptoms unique to RLB and cannot be confused with other known almond diseases.
Applying fungicides after RLB symptoms appear is ineffective, Trouillas said. The best thing growers can do at this point is to report symptomatic trees to researchers so they can track the prevalence and distribution of the disease.
Growers who see signs of this new disease in their orchard should contact their local UC Cooperative Extension farm advisor.
Preventive measures are the best way to manage RLB, Trouillas said. He urges concerned growers to think ahead to next winter/spring and plan for fungicide applications at petal fall and – if rains persist – also at two weeks and five weeks after petal fall. Fortunately, those are the same three key timings for managing other diseases, like shot hole and almond anthracnose.
“Because RLB is something that is introduced and potentially aggressive, it will be important for growers to keep that in mind next year and be on schedule for next year's spraying program,” Trouillas said.
Additional information on RLB can be found at https://www.sjvtandv.com/blog/first-detection-of-red-leaf-blotch-a-new-disease-of-almond-in-california.
Lawn-pocalypse! Surviving Drought
Ah, summer! The season of sunburns, pool parties, and… lawn droughts. If your once lush, green carpet now looks like a crunchy brown doormat, you're not alone. Let's dive into why your yard is staging a dramatic death scene and what you can do to...
Bermuda grass and weeds overtaking drought stressed turf grass.
Pendimethalin Use in California Rice: Clarifications and Updates
At our last meeting, we had some questions about the approved uses of pendimethalin in California rice. There are several products labeled for use on rice with pendimethalin as the active ingredient. As of June 2024, pendimethalin registered products (on...
Why Soldier Beetles Deserve the Aphid Belt
It's the Fourth of July and what better time to post images of the aptly name "soldier beetles" than today. These insects (family Cantharidae) resemble the uniforms of the British soldiers of the American Revolution, which is apparently how their name...
It's early morning, and a soldier beetle stirs in a Vacaville garden. A beneficial insect, it eats aphids and other soft-bodied insects. (Photo by Kathy Keatley Garvey)
Are the Red Coats coming? No, but this soldier beetle is alert. (Photo by Kathy Keatley Garvey)
UC Davis Entomology and Nematology Retiring Faculty Amass 247 Years of Service
247 years! The seven faculty members honored at the UC Davis Department of Entomology and Nematology's recent retirement luncheon amassed an amazing 247 years of service: UC Davis distinguished professor James Carey, 44 years, faculty member...
UC Davis distinguished professor James R. Carey, 44 years of service (Photo by Kathy Keatley Garvey)
UC Davis distinguished professor Richard "Rick" Karban, 42 years of service
UC Davis distinguished professor emerita Lynn Kimsey, 35 years of service. (Photo by Kathy Keatley Garvey)
Robert Kimsey, adjunct professor, 35 years of service (Photo by Kathy Keatley Garvey)
UC Davis distinguished professor Jay Rosenheim, 34 years of service. (Photo by Kathy Keatley Garvey)
UC Davis distinguished professor Diane Ullman, 29 years of service. (Photo by Jael Mackendorf)
Professor emerita Sharon Lawler, 28 years of service. (Photo by Kathy Keatley Garvey at UC Davis Picnic Day)
