Seed selection to combat alfalfa diseases | Agriculture

Alfalfa is Nebraska’s third most valuable crop. As you think about selecting alfalfa varieties to plant this year, be sure to consider varieties available with greater resistance to diseases. Anthracnose and phytophthora root rot are two of the most serious alfalfa diseases we are faced with here in Nebraska.

Phytophthora root rot is a major cause of seedling death and the most common root rot affecting all stages of alfalfa. This pathogen can cause seedling damping off in new followed plant death in wet conditions stands, occurring in as little as a few days. In established stands, Phytophthora root rot causes taproot issues resulting in up to a 50% yield loss and progressive decline over time and potential winter kill.

Anthracnose can appear anytime of the year on any age of alfalfa stand. Affecting the stems and crowns of the alfalfa plant, this disease can move rapidly and significantly lower alfalfa production in as little as one to two growing seasons. In some cases, disease stress can reduce alfalfa’s ability to withstand cold weather resulting in winter kill. Anthracnose spores readily spread from stem to stem and plant to plant through wind, rain and harvesting equipment.

There are multiple races of anthracnose that have been identified to cause economic damage to alfalfa in the Midwest, race 1, 2 and the newly discovered more aggressive race 5. Race 5 is a destructive race that often shows up earlier than previous races and during the first season of growth. Race 5 anthracnose is most aggressive during warm, moist and higher rainfall periods during mid-summer and fall.

While verified by the US Department of Agriculture in the Midwest, race 5 anthracnose has yet to be lab verified in Nebraska. Just because there isn’t lab verification yet, however, doesn’t mean it isn’t here. Even if not in the state yet, with alfalfa being a perennial crop, there is always the risk that race 5 shows up in the next few years. As such, planning ahead to deal with the disease by planting resistant varieties may be beneficial. Those wanting to avoid the risk should select a broadly resistant alfalfa variety, especially for those who have had issues with anthracnose previously.

Both of these diseases’ symptoms are most devastating on susceptible alfalfa varieties. Therefore, proper seed selection will be the first line of defense for disease management. Select varieties of alfalfa seed that have at least a moderate to high resistance to anthracnose and phytophthora root rot can effectively prevent yield and stand losses. New alfalfa varieties better able to withstand disease pressure, especially race 5 anthracnose, are coming to the market this year. Make sure to check with your seed dealer to get the variety that works best for your operation.

Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. He may be reached by phone at 402-254-6821 or email at ben.beckman@unl.edu.

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