Alfalfa can be a vigorous and productive forage crop for Kentucky farmers. Like all farm crops, however, alfalfa is subject to infectious diseases that can limit forage production. Managing these diseases is an important part of economical alfalfa production.
Alfalfa diseases can cause reduced forage yield, reduced forage quality, and decreased stand persistence. Sometimes, the effects of infectious diseases can be dramatic, such as sudden stand loss in a fall-seeded crop caused by Sclerotinia crown and stem rot. Often, the effects of diseases on alfalfa are more subtle but no less important. For example, alfalfa plants with Phytophthora root rot sometimes regrow slowly following cutting, resulting in a stunted stand showing no other obvious symptoms of disease.
Other diseases like bacterial wilt can kill a few scattered plants between each cutting. Over a period of a few seasons, this can result in a gradual yet substantial loss in plant stand. Also, several diseases predispose alfalfa to winter injury, such as crown rot diseases and Phytophthora root rot. In some cases, stand loss during the winter may be blamed on winterkill when an infectious disease ultimately may be involved.
Vincelli, Paul C.; Lacefield, Garry D.; and Henning, Jimmy C., "Managing Diseases of Alfalfa" (1990). Agriculture and Natural Resources Publications. 57.