Caused by the fungal pathogens Sclerotinia minor and S. sclerotiorum, lettuce drop occurs every year in the desert lettuce production areas of Arizona and California. The severity of disease is greatly influenced by moisture and temperature. Sclerotinia sclerotiorum can form aerial spores when lettuce bed moisture and temperature conditions are favorable. If rainfall events continue to occur during the remainder of this production season, followed by periods of mild temperatures and high relative humidity, the risk of airborne spore production and development of severe infections of lettuce drop will increase significantly. Lettuce drop is best managed by preventative applications of fungicides, usually when plants are small. The results from a lettuce drop fungicide efficacy trial conducted last year are available by sending an email request to me.
To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.