It’s Botrytis time for lettuce. The appearance of fuzzy gray growth at the base of maturing lettuce plants is a sign that the fungus Botrytis cinerea is present. The gray growth contains copious amounts of spores, which are dispersed in the air. When cool temperatures and high humidity prevail, spores landing on senescent or damaged lettuce tissue will germinate, then grow into healthy plant leaf and stem tissue, which can lead to plant collapse and death. This outcome is similar to that caused by Sclerotinia minor and S. sclerotiorum, the causal agents of lettuce drop. Botrytis and Sclerotinia are related fungal pathogens, and fungicides effective against one are usually active against the other. Fungicide applications are most beneficial when plants are young and gray mold is not yet present. The efficacy of later applications to older plants is not known.
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.