SoCal Desert Plant Pathology

SoCal Desert Plant Pathology is a resource for growers, pest control advisors, and agricultural professionals in Southern California desert regions, offering science-based updates on plant diseases, diagnostic tips, management strategies, and the latest research. Content is developed by Ana M. Pastrana, UC Cooperative Extension Plant Pathology Advisor.

Onion Downy Mildew Fungicide Efficacy Trial - 2025/26

June 4, 2026

By Ana Maria Pastrana Leon

A fungicide efficacy trial was conducted at the Emerald Seed Co. research farm in El Centro, CA, from September 2025 to March 2026 to evaluate the effectiveness of various fungicide treatments against onion downy mildew (Peronospora destructor) under field conditions. The trial included 9 treatments across 4…

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Iris Yellow Spot Virus (IYSV) Detected in Imperial Valley Onion Fields

April 27, 2026

By Ana Maria Pastrana Leon

Iris Yellow Spot Virus (IYSV) was a significant problem in bulb and seed fields in the Imperial Valley between approximately 2003 and 2012. Since then, growers and PCAs have reported limited occurrences, although symptoms can easily be misidentified as spray injury or other foliar diseases. In April 2026,…

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Emerging Viruses in Desert Cucurbits

March 31, 2026

By Ana Maria Pastrana Leon

Ana M. Pastrana1, Robert L. Gilbertson2, Tomás A. Melgarejo2, William M. Wintermantel3 1Plant Pathology Advisor, UCCE Imperial, Riverside, and San Diego; ampastrana@ucanr.edu; 2Department of Plant Pathology, UC Davis; 3USDA-ARS, Salinas Over the past few seasons, we have seen significant…

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