By Sam Markell
Importance. White mold is rarely a disease of economic importance in dryland field pea production but can be important in irrigated peas. The pathogen that causes white mold is the same pathogen that causes white mold on other broadleaf crops (canola, dry edible beans, soybeans, sunflower, etc…). Your fields may be at lower/higher risk depending on the history of white mold in your previous broadleaf crop, and the level of white mold in your current field peas could decrease/increase the white-mold risk to future broadleaf crops planted into that field in the future.
Symptoms. Lesions and white fluffy mold can occur on all above ground plant parts. Lesions being as water-soaked spots but take on the characteristic white, bleached color as they age. White fluffy growth may occur on lesions, particularly when canopies are wet for long periods of time. Sclerotia, black resting structures of the causal pathogen, are produced in and on diseased tissue.
Disease Cycle and Development. The disease cycle and favorable conditions for white mold on peas are essentially the same as on canola, dry edible beans, soybeans and other crops (sunflowers is a little different). The pathogen overwinters in the mouse-dropping size black fungal structures (sclerotia) at the end of the season. When adequate rain occurs in the spring and the soil is saturated (or near saturated), these sclerotia produce small mushrooms (apothecia) that release airborne spores. The infection process begins when spores land on flower petals, begin to digest them, and the subsequent fungal growth moves into healthy tissue. Consequently, field peas are not at risk for infection until bloom begins. For infection to occur, the soils must be wet enough to produce the small mushrooms 1-2 weeks before bloom. White mold is very dependent on cool and wet conditions for disease to develop.
Management. Data on the comparative efficacy of fungicides for control of white mold on field peas are not available, but testing conducted on other crops suggests that Proline and Aproach may be useful for managing white mold if applied when excellent fungicide deposition to the lower canopy can be achieved. If it is difficult to obtain excellent fungicide deposition to the lower canopy, Endura is likely to be the most effective registered product. Fungicide applications targeting white mold in field peas are unlikely to be profitable unless field peas are produced under irrigation and the weather is cool (highs in the 60s to 70s Fahrenheit) during bloom.