HPIPM: Aphanomyces Root Rot

Aphanomyces Root Rot (Scientific name)

Author: Howard F. Schwartz, David H. Gent, Martha Mikkelson, and Jack Rieggelman

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Cause

Aphanomyces root rot is caused by the fungus-like organism Aphanomyces euteiches, and is one of the most widespread and destructive diseases of pea.

Symptoms

Aphanomyces root rot symptoms first appear on primary and lateral roots as honey brown discolorations, but infected tissues quickly become soft and darker in color as the disease progresses. Severely infected plants are easily pulled out of the ground, leaving the outer cortical tissue in the soil. Top portions of infected plants are stunted and, in severe cases, wilt, yellow from the bottom of the plant upward, and die prematurely.

Impact of Disease

The disease reduces the number and size of pods, as well as seed size. Yield losses of 10 to 100% have been reported.

Life Cycle of the Pathogen

The pathogen can attack and infect pea at any growth stage, but infection generally occurs soon after emergence in heavily infested fields during wet weather. Soilborne dormant resting structures (oospores) or swimming spores (zoospores) germinate on the surface of pea roots, infect, and grow throughout the roots. One to two weeks after infection, oospores are produced in the infected tissue and serve as inoculum for following years. A low level of infection in one year can produce enough inoculum to cause economic damage to following pea crops for up 8 years. Infection can occur at most temperatures at which pea grows, but symptoms tend to develop most rapidly between 72 to 82ºF. Poorly drained soils favor infection, but the pathogen can also attack plants in well-drained soils kept wet by frequent irrigation. A complex of pathogens are often involved in Aphanomyces root rot, including fungi such as Fusarium and Pythium spp, but A. euteiches alone can damage pea. The pathogen can be disseminated between fields in infested soil and plant parts on equipment, and perhaps irrigation water. A. euteiches survives between pea crops as a pathogen on some weeds, but it primarily survives as dormant oospores that can persist for 10 years or longer.

Management Approaches

Biological Control

Oat planted as a winter cover crop can reduce compaction, improve drainage, and reduce Aphanomyces root rot severity.

Cultural Management Practices

Avoid planting pea in fields known to have inoculum levels. Avoid planting into compacted, poorly drained soils. Where Aphanomyces root rot is present, peas should not be planted into the field again for at least eight years or longer. Resistant varieties are being developed, but are not yet available commercially.

Chemical Management Program

No fungicides are currently registered for Aphanomyces root rot control. Using Treflan as an herbicide can give some control.

Consult pesticide labels for additional rate, application, and safety information. Additional information and current labels can be found at http://www.greenbook.net or http://www.cdms.net.

References

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.