US: Disease new to California threatens almond crops

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 confirmed the detection of P. amygdalinum. Formal pest confirmation by the California Dept. of Food and Agriculture is pending. 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 longstanding 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, Trouillas, who co-authored an explanatory article on the UCCE San Joaquin ...