Sclerotinia Stem Rot

Sclerotinia Stem Rot

Sclerotinia stem rot is a disease of soybean that has been showing a steady increase in incidence in Nebraska for the last two years. The disease is caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary. The causal organism has a very broad host range. The fungus also causes stem rot and the disease white mold on hosts from 64 plant families, 225 genera, and 361 species. Included in the list are dry beans, sunflowers, canola, alfalfa, cabbage, lettuce, tomato and potato. The fungus survives from year to year as sclerotia in plant debris, mixed with seed or in the soil. Sclerotia germinate in late spring or early summer and produce apothecia or mycelium. Apothecia are capable of producing millions of airborne ascospores almost daily over a 7 to 10-day period if favorable environmental conditions prevail. Primary infection occurs on senescing blossoms or injured tissue. Free moisture must be present on the plant surface for infection to occur. When blossoms are infected the fungus obtains the nutrients necessary for appressoria production and then colonizes healthy tissue via direct penetration. Disease development is favored by cool, wet temperatures and a thick canopy (narrow row spacing. Secondary spread occurs when healthy tissue comes into contact with mycelium produced on infected plants. This commonly occurs when plants lodge. Sclerotia produced on plant tissue may remain attached to debris, be released onto the soil or be harvested and contaminate the seed. If seed is not thoroughly cleaned, sclerotia may be planted along with seed the following season. Contaminated seed is the most common means of spreading the disease to new fields.

Symptoms

Initial symptoms begin to appear during pod development. Leaves wilt and plants turn gray-green before turning brown and dying. One of the primary signs of a Sclerotinia infection is the presence of white mycelial growth on flowers, stems and pods. Sclerotia later develop in the mycelial mats. Infected stems are initially water-soaked then become tan and eventually bleached. Stem infections may result in girdling and lodging. Bleached stems have a pithy texture and shred easily. Sclerotia may be found both externally and inside infected stems.

Plant Health Management

Implement Cultural Practices That Promote Good Air Circulation

Included in this category are: adequate row spacing (greater than 15 inches), avoid overhead irrigation during flowering, and fertilize at recommended rates to avoid excess canopy development.

Plant Clean Seed (Free of Sclerotia)

Crop Rotation.

Rotate to monocots such as corn, sorghum or wheat.

Resistant Cultivars

Resistance is available in type 4 and 5 cultivars but in type 3, commonly grown in Nebraska. Williams has been shown to be highly susceptible to it is best to use cultivars that do not have it in their background in areas where the disease is known to exist.

References

Purdy, L.H. 1958. Some factors affecting penetration and infection by Sclerotinia sclerotiorum. Phytopathology 48: 605-609.

Sinclair, J.B. and P. A. Backman, eds. 1989. Compendium of soybean diseases, 3^rd ed. American Phytopathological Society, St. Paul, MN. 106 pp.

Steadman, J.R., S. Rutledge, D. Merrell and D.S. Wysong.1995. Sclerotinia stem rot of soybeans. Univ. Nebraska Coop Ext. Ser., Agric. Expt. Sta. and Inst. of Agriculture and Natural Resources G95-1270-A.

Useful Links

Purdue University

Iowa State University

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before buying and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

Questions, Comments, Complaints and Complements?

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by:

Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln
Dr. D.C. Erwin, Department of Plant Pathology, University of California-Riverside

This page is authored and maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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