2002-2004 Specialty Crops Research Program
University of California

Principal Investigators: Steve Koike, Richard Smith and Eric Brennan

Project title: Investigation of Organic Seed Treatments for Spinach Disease Control

Historically, the regulations governing organic production systems allowed for conventional fungicide treatments to be used on seed planted in organic fields. However, in October 2002 national regulations will prohibit this practice. Spinach crops, which are an important organic vegetable commodity in California, may suffer significant loss of quality and yields due to this change. Unprotected spinach seeds and seedlings are extremely sensitive to soilborne damping-off pathogens. Fresh market spinach is planted at very high seeding rates that enable damping-off organisms to quickly spread throughout the planting. The planting of unprotected spinach seeds therefore could result in tremendous losses for organic producers and could make the crop uneconomical to produce. During a focus session in June 2002, leaders in the organic industry in coastal California identified spinach seed treatments as one of the key issues facing their industry.

The first objective of our proposal is to document the occurrence and severity of spinach damping-off disease as it develops in the organic industry after the elimination of conventional fungicide seed treatments. We will conduct surveys in organic spinach fields by evaluating disease severity. We will then document the cause of the problem by collecting samples from these fields and analyzing them for the presence of Pythium, Fusarium, Rhizoctonia, or other spinach root and crown pathogens. Samples will be processed in the UCCE diagnostic laboratory in Salinas.

The second objective will be to field test various chemical and biological substances that will be allowed in organic production systems. Locations having histories of damping-off disease will be the first fields selected for these experiments. We plan to conduct these studies at commercial sites as well as at the USDA certified organic research plots in Salinas. Experimental design will be randomized complete blocks with four to six replications. Seeds treated with the various materials will be planted and resulting disease incidence will be recorded. Crop stands, yields, and quality will also be assessed. Representative plants will also be collected and analyzed for pathogens.

The third objective will be to extend our findings to the organic agricultural community. Potentially useful treatments will be field tested in larger demonstration plots to further test efficacy and provide opportunities for growers and field personnel to evaluate the treatments. Our findings will also be presented at extension meetings and organic production meetings. Impact will be assessed by following up with clientele who adopt and use recommended treatments. Disease assessments will be made at these fields.