DISEASES OF ALFALFA - CROWN ROT

Because of our poor understanding of the epidemiology of crown rot, adequate controls are not available. In general, severe crown rot is thought to indicate that plants are under stress, thus making plants more susceptible to infections by crown rot pathogens. Stress factors may include biological factors such as infection by other pathogens, or wounding by soil insects. Other factors influencing crown rot development may be physical in nature, such as nutrient, water, heat or cold stress. At this time management of crown rot primarily involves monitoring and assessing alfalfa stands to quantify crown rot levels. Information from such assessments can then be used to make decisions about maintaining or replacing an alfalfa stand.

A common soil insect that may have a major impact on crown rot development is the clover root curculio. This insect attacks legume forage crops such as clover and alfalfa, feeding on roots, and leaving trails that are easily visible to the naked eye (see arrows). The clover root curculio is of interest from a pathological standpoint because the wounds that it makes while feeding can serve as entry points for fungal and bacterial crown rot pathogens. In addition, there is some evidence that the clover root curculio may actually move alfalfa crown rot pathogens from plant to plant. There is no successful method of controlling the clover root curculio in an established alfalfa stand. Long term control is possible by rotating away from host crops for several years before reestablishing alfalfa at a given location.