Cause Physoderma alfalfae (syn. Cladochytrium alfalfae, Urophlyctis alfalfae) is a soilborne fungus that will survive in soil indefinitely as resting sporangia. Under favorable, wet conditions, the sporangia release zoospores, which penetrate crown buds. The disease is frequent on bottomlands where there is plenty of moisture. It has not been reported from Washington.
Though all varieties tested at OSU were susceptible, some were less susceptible than others. These varieties include Talent, Socheville, DuPuits, Sevelra, and Vernal. Very susceptible varieties included Buffalo, Lahontan, Ranger, and Rhizoma.
Symptoms Large, knobby swellings on crown and roots. The plant becomes stunted, unthrifty, and often dies.
Cultural control
- Provide good soil drainage.
- Plant least susceptible varieties.
- Avoid excessive irrigation.
- Avoid planting alfalfa on land with a history of the disease.