First Report of White Mold Caused by Sclerotinia minor on Mexican Sunflower in California

Mexican sunflower (Tithonia rotundifolia) is a plant in the Asteraceae that is grown commercially as a cutflower commodity and also as a beneficial insectary plant. In June 2012 in coastal California (Santa Cruz County), several fields of organic lettuce (Lactuca sativa) were interplanted with direct-seeded rows of Mexican sunflower (cv. Torch) in order to attract beneficial insects. When approximately 2 to 3 weeks from harvest, lettuce plants began to wilt and collapse. Lettuce crowns were decayed and covered with white mycelium and small (0.5 to 3 mm diameter), irregularly shaped, black sclerotia. These plants were confirmed to have lettuce drop disease caused by Sclerotinia minor (2). In addition, Mexican sunflower plants began to wilt and eventually died. Initial symptoms on crowns and bases of the main stems in contact with soil consisted of a light tan discoloration. These discolored areas turned darker brown, became necrotic, and later were covered with white mycelium and sclerotia that were identi...