Utah Plant Disease Control No. 47
January 1995
Selecting Alfalfa Cultivars with Disease Resistance
National Alfalfa Alliance Cultivar List (2007/2008)
Several diseases can cause yield loss and stand decline in irrigated alfalfa in Utah. The most important of these are Verticillium wilt, caused by the fungus Verticillium albo-atrum, and Phytophthora root rot, caused by the fungus Phytophthora megasperma f. Sp. medicaginis. Other diseases of lesser importance are northern root-knot nematode; common leaf spot, caused by the fungus Pseudopeziza medicaginis; spring black stem, caused by the fungus Phoma medicaginis var. medicaginis; downy mildew, caused by the fungus Peronospora trifoliorum; and bacterial stem blight, caused by the bacterium Pseudomonas syringae pv syringae. Witches broom, caused by a mycoplasma, is only important in the Uintah Basin.
These diseases can decrease yield and quality of alfalfa. Perhaps more importantly, the stem nematode Phytophthora root rot, Verticillium wilt, and Bacterial wilt all cause stand decline by killing individual plants and by predisposing plants to winter kill. This reduces the yield potential and useful life of an alfalfa field.
Because of the importance of diseases throughout the United States, plant breeders have developed alfalfa "cultivars" (cultivated varieties) with resistance to one or more of these diseases. Selection of cultivars with resistance to the principal diseases of a region is the most important and economical means of controlling alfalfa diseases.
The presence and severity of alfalfa diseases varies throughout Utah. Differing climates, soil types, and agronomic practices create conditions favorable for certain diseases and not others. Also, because of the particular genetics in alfalfa, even highly resistant cultivars have individual plants that are susceptible to disease. To obtain optimal yield and stand longevity, cultivars with as high a level of resistance as possible to disease should be selected.
The purpose of this bulletin is to provide a comprehensive list of certified alfalfa cultivars with disease resistance that are sufficiently winter-hardy for use in Utah. Information on the performance of some of these cultivars under local conditions can be obtained through your county extension office. Consider that cultivar performance trials are often not located in areas with high disease pressure. Susceptible cultivars that yield well in the absence of disease may perform poorly in a field where disease is present. High yields from susceptible cultivars in field trials may be misleading and should never be the primary basis for cultivar selection.
The list of disease-resistant cultivars provided in this bulletin are for use in irrigated alfalfa produc-tion where diseases are more common. Stand decline diseases are generally worse in furrow than in sprinkler irrigated fields, except for verticillium wilt which is equally severe in both. Relatively few diseases attack alfalfa grown under dryland conditions in Utah, so no list is provided.
Contact your county agent if you observe disease problems that you wish to have diagnosed at the Utah State University Plant Diagnostic Laboratory. Your agent will provide you with information on how to collect and prepare a proper sample for diagnosis. Knowing which diseases are present in a field is the most important factor in selecting a suitable cultivar.
Check Below for a list of Certified Alfalfa Cultivars
Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
Listing of commercial products implies no endorsement by the authors or the Utah State Cooperative Extension Service. Criticism of products not listed is neither implied nor intended. Persons using such products are responsible for their use according to the current label directions of the manufacturer. Pesticide labels are legal documents, and it is a violation of federal and state laws to use a pesticide inconsistent with its labeling. The pesticide applicator is legally responsible for its prope
use. Always read and follow the label.
- Certified Alfalfa Cultivars - Fall Dormancy 1
- Certified Alfalfa Cultivars - Fall Dormancy 2
- Certified Alfalfa Cultivars - Fall Dormancy 3
- Certified Alfalfa Cultivars - Fall Dormancy 4