Sclerotinia Stem Blight In Soybeans

Nathan Kleczewski Ph.D
Extension Specialist- Plant Pathology
Assistant ProfessorDepartment of Plant and Soil Sciences

We have had a few reports of sclerotinia stem blight (white mold) on soybeans grown in the mid-Atlantic. This is a cool season disease that we see almost every year, but only to a very small degree. Often you will see it in high yield environments and in shaded areas of the field, such as along wood edges. The fungus overwinters as small, pebble-like structures in the soil which germinate to directly infect plants or produce a mushroom-like structure that can produce millions of spores over several days.  Sclerotinia spores are wimpy and require dead/dying tissues to germinate and take hold.  This is why we see the fungus cause issues during flowering- spores will land on decaying flower petals and grow into the flower and eventually the stem.  Over time lesions with distinct margins develop and more of the black pebble-like structures may be observed in or on the stem.  Affected plants may wilt or mature prematurely.

Sclerotinia stem blight. Note the black structures on the stem and sharp lesion edges. Photo: C. Whaley.

If you notice Sclerotinia stem blight (white mold) in your field it is likely there to stay. The best management practice at this point in full season beans is to schedule infested fields to be harvested last to minimize spread of the pathogen from field to field on farm equipment.  Hot weather is not favorable for this disease and only a few days of hot dry weather are needed to burn out Sclerotinia.

In soybeans planted into fields with a known history of Sclerotinia stem blight, and when weather is cool and wet, applications targeting the R1-R2 stage are the most efficacious.   Example fungicides for SSB suppression include labeled group 1’s (Topsin), labeled group 3’s (Proline, Domark, Topguard), Fluazinam (Omega); labeled group 7’s (Endura) and labeled group 11’s (Aproach). Often fungicide applications are not justified in Delaware or Maryland but they can be beneficial under some circumstances. As usual, preventative applications are most efficacious.

Source : udel.edu