HPIPM:White Mold Sunflower

From Bugwoodwiki

Author: Howard F. Schwartz

Sclerotinia rot Photo by Howard F. Schwartz, Colorado State University, Bugwood.org Taxonomy Kingdom: Fungi Phylum: Ascomycota Class: Leotiomycetes Order: Helotiales Family: Sclerotiniaceae Genus: Sclerotinia Species: sclerotiorum Scientific Name Sclerotinia sclerotiorum (Lib.) de Bary Common Name Synonyms White mold of dry beans, Sclerotinia stem rot, timber rot, white mold

White mold is the most destructive disease of sunflower. Symptoms include wilting, middle stalk rot, and head rot. The wilt symptom is most common because the fungus survives in the soil and first attacks the roots. A dark canker forms at the base of the plant and eventually girdles the stem. In advanced stages, the pith decays and the stalk becomes shredded. Also, hard black resting structures of the fungus, known as sclerotia, form at or near the stem base. They can be found in the pith or outside on the stem, and are an excellent identification aid for the fungus. Middle stalk rot and head rot usually begin as gray, water-soaked lesions on the upper stem and fleshy part of the head. In the stalk, a dense snowy white fungal growth and some sclerotia will often be produced. On the head, the entire seed layer falls away leaving only a bleached, shredded skeleton interspersed with large sclerotia.

Favored by cool weather, and high rainfall or irrigation.

Manage the disease by planting in non-infested fields, extended crop rotations with non-host crops (wheat, corn, sorghum), weed control, avoiding high nitrogen rates, reducing plant populations, and timely application of fungicides.

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