Prior to the identification of Race 2, no race numbers were assigned to Aphanomyces resistance, but in the future all Aphanomyces -resistant varieties probably will be identified according to race. If a resistant variety does not have a race designation, it is safe to assume it has only Race 1 resistance. Both races occur in Iowa, and based on our 1994 survey, Race 2 is common. So for the best genetic resistance against seedling disease, it is probably best to use a variety resistant to both races. Effect of Aphanomyces soil infestation on susceptible variety Vernal.
Noninfested soil is on the right.
To protect against Pythium , a fungicidal seed treatment is needed. Apron or Apron XL seed treatments are effective against Pythium and Phytophthora , but there are no registered seed treatments that have been shown to be effective against Aphanomyces . Ridomil and Ridomil Gold are soil fungicides registered for use in establishing alfalfa. Some studies have shown that a soil fungicide applied at seeding can be beneficial, but seed treatment appears to be a more cost-effective way to control Pythium and Phytophthora . A soil fungicide is more likely to pay off if soil conditions are extremely wet during or shortly after planting.