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UC works to protect spinach from downy mildew

The Issue

Spinach is a key leafy green vegetable commodity in California. It is a versatile vegetable item that can be eaten fresh or cooked and which contains high levels of vitamins, nutrients and antioxidants. California produces more than 60 percent of the country’s spinach. Monterey County alone grows close to 10,000 acres, which is about half of the state's spinach crop. As with many other commodities, California growers are known nationwide for producing large volumes of spinach that have extremely high quality standards.

However, downy mildew is a very serious disease of spinach and causes the leaves to turn bright yellow and then brown. Growers have struggled against this disease for years and continue to battle this fungus. In the past three years, a number of serious downy mildew outbreaks have occurred in the coastal Salinas Valley and other spinach-producing areas.

What Has ANR Done?

Because of the importance of this persistent downy mildew problem, Steven Koike, UC Cooperative Extension advisor, is part of an extensive coalition that seeks answers through research to solve this challenge. This group is made up of farm advisors, researchers from other universities, USDA researchers, growers, pest control advisers, the California Leafy Greens Research Board, commercial spinach breeders and members of the seed industry.

Farm advisors collect samples of diseased spinach from throughout the state and submit these to the testing lab in Salinas. Using a live spinach plant assay, samples are tested by UCCE in Monterey County to determine the race of the mildew causing the outbreaks. This assay by UCCE is the state's only public testing program that can identify different races of spinach downy mildew.

The Payoff

Research coalition led by UCCE identifies new spinach downy mildew races

Together with the University of Arkansas, UCCE has discovered four new, resistance-breaking strains of the downy mildew fungus that have occurred on spinach since 2009. Each new race damages previously resistant spinach cultivars and forces the industry to develop new resistant cultivars. Without a knowledge of which races are occurring in the state, progress cannot be made in developing new spinach lines; therefore, this race identification program is critical to the health of the spinach industry. If left unchecked, downy mildew will severely damage the spinach industry, which in Monterey County is valued at approximately $128 million.


Supporting Unit: Monterey County

Steven T. Koike, UCCE advisor in Monterey County, plant pathology, (831) 759-7350, stkoike@ucdavis.edu