Rhizoctonia Damping-Off and Stem Rot of Soybeans

AC-25
Date: 
10/12/2010
Anne E. Dorrance and Dennis R. Mills, Department of Plant Pathology

Rhizoctonia damping-off and stem rot of soybeans can cause early season stand losses as well as premature yellowing in soybeans. Rhizoctonia is present in all Ohio soils at some level. The stem rot phase can occur at any time during the growing season but generally causes less damage than the damping-off phase.

Symptoms


Rhizoctonia stem rot—yellowed, stunted, infected plants in the field.

Rhizoctonia damage may occur at any time during the growing season, but it is more severe on young seedlings. Rhizoctonia solani can cause seed rot, root rot, and lesions on hypocotyls. Damping-off occurs when germinating seedlings are infected prior to or just after emergence. On hypocotyls, lesions are reddish-brown and sunken. Diseased seedlings collapse from the firm, dry canker that girdles the hypocotyl. Diseased older plants become chlorotic, resembling plants with nitrogen deficiency. Symptoms on older plants, or on those plants that survive seedling infections, include the characteristic sunken, reddish-brown cankers on the lower stem near the soil surface. Disease losses result from stand reduction in newly planted fields and premature death of diseased plants that produce undersized seed.

Damage caused by Rhizoctonia is frequently confused with diseases caused by other seedling pathogens. It is very difficult to identify the pathogen that causes preemergence damping-off. The symptoms are very similar for Pythium, Phytophthora, and Rhizoctonia. Rhizoctonia-infected plants typically have characteristic and distinct reddish-brown, sunken cankers on the lower stem or hypocotyl. Older plants with Phytophthora stem rot have chocolate brown lesions that extend up the stem several nodes on older plants.

Disease Cycle

Rhizoctonia stem rot and damping-off are caused by the soil-borne fungus Rhizoctonia solani. This fungus exists as different types that are capable of causing diseases on different host plants. The types that affect soybeans can also infect other legume crops, sugar beets, some vegetable crops and weeds. It survives in soil as sclerotia and on decaying plant material as mycelium.

The damping-off and stem rot phases of the disease may occur in both light, well-drained, and in heavy, poorly drained soils. Rhizoctonia solani collected in Ohio can infect soybeans across a wide temperature range (60°–95°F) and from low soil moisture (25%) to saturated conditions.

Premature yellowing caused by Rhizoctonia solani, stem rot. Characteristic reddish-brown sunken cankers on the hypocotyl caused by Rhizoctonia solani.

Best Management Practice for the Seed and Seedling Phases of this Disease

  1. Fungicide seed treatment.
  2. Varietal differences have been noted but routine screening for resistance is available from few sources.
  3. Crop rotation with wheat and corn to allow for soybean residues to degrade.
  4. Improve soil drainage.
  5. Based on soil tests, adequate fertilization but not over fertilization.

For more information on managing Rhizoctonia visit:

The Ohio Field Crop Disease website: oardc.ohio-state.edu/ohiofieldcropdisease

Program Area(s): 
Ohioline http://ohioline.osu.edu