Cause A fungus-like microorganism, Aphanomyces euteiches f. sp. pisi, that overwinters as thick-walled oospores, which can be spread by water, wind, infected plant debris, soil movement, or by tillage equipment. Oospores are produced within infected root tissue, which decomposes, releasing the oospores into surrounding soil. The fungus can infect and multiply in other legume roots, such as clover, alfalfa, lentil, Cava bean, and common bean. Even without other hosts, the pathogen can persist in infested soils 10 years or more, though the population slowly decreases with time.
Symptoms First are long, soft, water-soaked areas on the lower stem and roots; they rapidly turn tan and spread throughout the root system. Peas with severely infected roots pull out of the ground easily, and the outer portion (cortical tissue) is easily stripped away, leaving only interior tissues. Cortical tissues can be observed with a compound microscope, and diagnostic oospores (25 to 30 microns with an oil globule in the center) are readily detected. Top portions of infected plants are stunted and, in severe cases, wilt, yellow, and die prematurely.
- Long rotations are the best way to manage the disease.
- Green manure plowdowns of oat and Brassica residues has helped somewhat to reduce inoculum levels.
- Select well-drained fields. Avoid fields with excessive soil compaction.
- Avoid fields heavily infested with the pathogen. Test soil to determine inoculum levels in a given field.
- Do not plant late-maturing varieties in fields with a history of this root rot.
Chemical control Currently, no fungicide is registered as a seed treatment or for in-furrow application. Using Treflan as a herbicide can give some control. Small yield increases were reported in other states when label rates of trifluralin were used for weed control.
Biological control No biocontrol agents that have demonstrated effective control are available.
References Frits, V.A., Allamaras, R.R., Pfleger, F.L., and Davis, D.W. 1995. Oat residue and soil compaction influences on common root rot (Aphanomyces euteiches) of peas in fine textured soil. Plant and Soil 171:235-244.
Harvey, R.G., Hagedorn, D.J., and DeLoughery, R.L. 1975. Influence of herbicides on root rot in processing peas. Crop Science 15:67-71.
Kraft, J.M., Marchinkowska, J., and Muehlbauer, F.J. 1990. Detection of Aphanomyces euteiches in field soil from northern Idaho by a wet-sieving/baiting technique. Plant Disease 74:716-718.