Verticillium wilt is a constant threat because some farmers are still growing old varieties that lack resistance to this disease. Nearly all alfalfa varieties currently grown in Ohio have resistance to bacterial wilt and Fusarium wilt. The widespread use of resistant varieties has greatly diminished the significance of wilt diseases. It is caused by a soilborne fungus that becomes active under wet soil conditions and may attack both seedlings and older plants. Dark brown, decayed areas on the tap root two to three inches below the soil surface are early indicators of Phytophthora root rot.
Soil moisture is the key factor affecting disease development.
Any improvement in surface and subsurface drainage will reduce losses from this disease as well as from other less common root rots. Varieties with good levels of resistance are now available. Phytophthora specific fungicide seed treatments are available to help prevent loss of stands due to seedling damping-off. Fungicides are labeled for use at planting either as a broadcast application or incorporated on fertilizer granules and applied in a band beneath the seed. Aphanomyces root rot may contribute to poor alfalfa establishment and reduced growth in wet soils.