Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Bean, Snap (Phaseolus vulgaris) -- Fusarium Root Rot
 
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 capscity. Anything which impedes root growth such as cold or compacted soils also favors the disease.
Symptoms: The main root may show a red discoloration, later turning brown and decaying. Infections seldom spread into tissues above ground level. Small side roots die and, above them, secondary roots develop which may become infected and die. These secondary roots help maintain the plant and help the crop develop when the tap root is severely diseased. In severe cases, plants are stunted; leaves are yellowish and often drop early.

Note poor root development on infected plants (right).

Note the red discoloration of the main root.
 
Cultural control:
  1. Plant in well-drained soil when possible.
  2. Avoid compacted soils or minimize soil compaction with deep ripping to avoid hard pans.
  3. Rotate into grass or small grain crops between bean crops, 5 to 6 years is better but 3 to 4 year rotations are more common.
  4. Till 18 inches below the row just before planting. Root rot is not decreased, but better root formation offsets the disease's effect on the plant. This treatment is especially effective on heavy soils or in soils that have a plow pan.
  5. Hilling vines is helpful because it promotes adventitious root production.
  6. Use resistant or tolerant cultivars if available.
Biological control: Efficacy of the following products in the Pacific Northwest is unknown.
  1. Kodiak Flowable at 0.25 fl. oz/100 lbs seed is registered to provide suppression of Fusarium and Rhizoctonia spp. 4-hr reentry.
  2. T-22 Planter Box (Trichoderma harzianum) is registered as a seed treatment in Washington. Do not use in alkaline soils or if soil is below 50°F.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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