According to a survey we did in 1994, Aphanomyces is more common than Phytophthora in Iowa soils, and these two fungi should be considered equal threats to seedlings. Like in other crops, alfalfa seedling diseases are more severe in wet conditions. Unlike other crops, alfalfa seedlings are very cold tolerant. Therefore, it is not necessary to delay planting to avoid disease, unless conditions are too wet. Effect of Aphanomyces soil infestation on susceptible variety Vernal.
Noninfested soil is on the right.
A resistant variety is on the left. The best way to avoid seedling diseases is to plant varieties with an R or HR resistance rating to both Phytophthora and Aphanomyces . To protect against Pythium , a fungicidal seed treatment is needed. Apron seed treatment is effective against Pythium and Phytophthora , but there are no registered seed treatments that have been shown to be effective against Aphanomyces . Ridomil is a soil fungicide registered for use in establishing alfalfa.