Collar rot

The symptomatically described disease Southern blight is often the first observed precursor of the collar rot caused by the fungus Agroathelia rolfsii. Causally known as Sclerotial blight, Agroathelia rolfsii survives in the soil as sclerotia, and in infected decomposing plant material as mycelia.

Collar rot that is caused by the oomycete Phytophthora is causally called Phytophthora collar rot, and is a common disease of fruit and nut trees, as well as other flowers and crops. Phytophthora species remain in the soil, as spores, and in infected plant tissue, as mycelia, so absent control measures (sterilization, toxic applications) the disease continues so long as susceptible plants are grown in that soil.

Hosts and agents

• In carnations (Dianthus caryophyllus) by Alternaria dianthi,
• In chili (Capsicum) by Phytophthora,
• In cinchona (Cinchona officinalis) by Phytophthora quininea,
• In Chinese evergreens (Aglaonema) by Fusarium subgutinans,
• In coffee plants (Coffea) by Gibberella stilboides,
• In dogwoods (genus Cornus) by Phytophthora cactorum where the disease is also called "crown canker",
• In eggplant/brinjal (Solanum melongena) by Sclerotinia sclerotiorum and Sclerotium rolfsii,
• In elephant foot yams (Amorphophallus paeoniifolius) by Sclerotium rolfsii,
• In fruit and nut trees by a variety of pathogens including Sclerotium rolfsii, Alternaria and Phytophthora,
• In groundnut/peanut (Arachis hypogaea) by Aspergillus niger which also causes wilt and crown rot, and by Lasiodiplodia theobromae,
• In hardwoods and conifers by Phytophthora cinnamomi,
• In maize (corn, Zea mays) by Sclerotium rolfsii,
• In papaya by Calonectria,
• In pines by both Phytophthora and Diplodia pinastri,
• In rhododendron, China aster, marigold, gloxinia and zinnia by Phytophthora cryptogea,
• In sunflowers by Sclerotium rolfsii, and by Phytophthora cryptogea.
• In sweet potatoes (Ipomoea batatas) by Sclerotium rolfsii,
• In tobacco by Sclerotinia sclerotiorum.
• In tomatoes (Solanum lycopersicum) by Alternaria solani,