Pathogen profile: Sclerotium

Sclerotium is a fungal pathogen that can cause considerable crop damage, but it is more common in the warmer climates of the southern United States. It can be brought to the northern United States and Canada on infected plants grown in the southern regions.

The most common species that attacks greenhouse crops is Sclerotium rolfsii. Sclerotium rolfsii occurs in outdoor soil, so it commonly infects beans, beets, carrots, corn, cucurbits, onions, peanut, peppers, potatoes, rice, tomatoes, watermelon and wheat, but it can also infect greenhouse crops such as chrysanthemum, iris, lilies, narcissus and zinnias. It is aggressive and grows very rapidly compared to most fungal plant pathogens.

There is some confusion due to the similarities in the names of the disease-causing fungi Sclerotium rolfsii and Sclerotinia. They are not the same fungal species, even though they have a similar appearance, as they produce white hyphae. Both produce sclerotia, or resting bodies, but they are different colors. However, Sclerotinia only produces acrospores that are released from cup-shaped fungal bodies called apothecia. Sclerotium rolfsii is active in warm to hot temperatures whereas Sclerotinia is most active at cool temperatures. Lastly, Sclerotinia only infects broadleaf dicots, whereas Sclerotium rolfsii infects both dicots and some narrowleaf monocots, such as wheat and onions.

Read more at PRO-MIX (Troy Buechel)