Scout for alfalfa crown and root rots

Crown and root rots are commonly observed in alfalfa fields in South Dakota. They are especially common in alfalfa stands that are 2 or more years old. Various fungal pathogens cause these diseases. To learn how to minimize crown and root rot infections.

Crown and root rots are common diseases that attack alfalfa in South Dakota. These rots are more common in stands 2 or more years old. Infected crowns are dark brown or bluish-black in color (Fig. A). The dark rotted portion of the crown are soft and easily break off when pulled from the ground. Symptoms progress as the plants become older, producing fewer buds and eventually the whole plant may die after several seasons (Fig B and C).

Various plant stresses increase the speed of the crown and root rot development. These include: foliar diseases, foliar and root insects, frequent or untimely harvests, early frosts, poor fertility, winter injury and low soil pH.

To ensure longevity of alfalfa stand and reduce crown and root rots, growers should practice the following:

· Select winter-hardy alfalfa varieties with known resistance to crown and root rot pathogens.

· Minimize crop damage by controlling insect pests.

· Adjust soil pH to 6.6-7.5 by liming.

· Irrigate prior to cutting but delay irrigation until regrowth has began.

· Maintain adequate fertility levels especially phosphorus and potassium in poorly fertilized soils.

· Avoid overgrazing and heavy traffic.

· Maintain proper cutting schedule.