The most important fungi attacking alfalfa seedlings are Aphanomyces euteiches , Phytophthora medicaginis , and several species of Pythium . Seedling diseases should be suspected when emergence is poor or there are stunted, discolored, or dead seedlings. Like seedling diseases of other crops, alfalfa seedling diseases are more severe in wet conditions. Although cold soils also promote seedling diseases in general, alfalfa seedlings are more cold-tolerant than other crop seedlings, so soil temperature is not a major concern for alfalfa seedling diseases. A resistant variety is on the left.
Genetic resistance is the best way to avoid seedling diseases or any other alfalfa disease.
The Iowa State University Crop Performance Test report shows disease resistance for all the varieties entered in the test. This report is available at county extension offices or from the Extension Distribution Center on campus. For seedling disease protection, it is best to plant varieties with an R or HR resistance rating to both Phytophthora and Aphanomyces . Recently, some seed companies have begun to market varieties with resistance to races 1 and 2 of A. euteiches . In the future, all Aphanomyces -resistant varieties probably will be identified according to race.