Plant Disease Management Handbook

Cause The fungus, Rhizoctonia solani (sexual stage: Thanatephorus cucumeris), causes root rot of many plant species. It overwinters in soil or plant debris and can survive many years as sclerotia or chlamydospores. Moderate temperatures (less than 70°F) are favorable for disease development. Seedlings are quite susceptible to Rhizoctonia.

Snap bean plant with Rhizoctonia root rot.

OSU Plant Clinic Collection, 2017.

Close-up of a snap bean plant with Rhizoctonia root rot.

OSU Plant Clinic Collection, 2017.

Close-up of snap bean plants with reddish-brown lesions on the hypocotyl.

OSU Plant Clinic Collection, 2017.

By C. M. Ocamb and R. B. McReynolds, Oregon State University Extension

See:

Bean, Snap (Phaseolus vulgaris) - Strategies for Controlling White and Gray Mold in the Same Field

Image related to Bean, Snap (Phaseolus vulgaris)-Gray Mold

Necrotic lesions on the pods and stem.

Photo by Paul Koepsell, 1974.

Cause The fungus, Fusarium solani f. sp. phaseoli, can survive in soil for many years. It persists on infected bean straw and spreads when the straw is moved. Wind and water can move infested soil and debris. The disease is favored by extremes in soil moisture (too dry or too wet) and is less severe when moisture is near field capacity. Anything, which impedes root growth such as cold or compacted soils also favors the disease.

Several snap bean plants showing rot on the primary and secondary roots. Photo by Cynthia M. Ocamb, 2020.

Image related to Bean, Snap (Phaseolus vulgaris)-Fusarium Root Rot

Note poor root development on infected plants (right).

Photo by Paul Koepsell, 1978.

Roots of a snap bean plant showing the reddish-brown discoloration due to Fusarium root rot.

Photo by Cynthia M. Ocamb, 2020.

Several snap bean plants showing rot on the primary and secondary roots.

Photo by Cynthia M. Ocamb, 2020.

A snap bean plant where nearly the entire length of all roots are exhibiting root rot and a dark brown lesion has developed along the lower portion of the hypocotyl.

Photo by Cynthia M. Ocamb, 2020.

See:

Bean, All (Phaseolus vulgaris) - Damping-off and Stem Rot

Cause Clover yellow vein virus (CYVV) is transmitted by the green peach aphid, pea aphid, black bean aphid, and clover aphid. Two or three subspecies of Trifolium repens (white clover) are the principal virus reservoirs in western Oregon. Clover yellow vein virus and strains of bean yellow mosaic virus often are in the same field.

Cause Bacterial brown spot is caused by the bacterium, Pseudomonas syringae pv. syringae, which can overwinter on bean and several leguminous weed species. It can also contaminate seed, but the role of such inoculum in disease development is not well understood. Sprinkler irrigation and leaf rubbing can spread the disease. Data from the University of Wisconsin indicate that disease development correlates with the intensity of water droplet impacts on leaves.