Healthy roots, stems and leaves lead to higher alfalfa yield potential. Aboveground, stems and leaves produce and transport plant energy to make valuable forage. Below-ground, alfalfa roots gather water and nutrients. While the soil holds many components alfalfa plants need to thrive, it can also contain destructive soilborne diseases like aphanomyces root rot, anthracnose, pythium and phytophthora root rot.
Diseases can limit key plant processes, negatively impacting forage yield and quality potential. Understanding these costly threats and prioritizing improved disease resistance packages can help you establish stronger stands, healthier plants and higher yield potential.
Aphanomyces root rot
Strong, healthy roots allow alfalfa plants to gather more soil nutrients and water to support a high-producing plant while fixing more nitrogen in the soil from healthy nodulation. In seedlings, the aphanomyces disease causes root pruning and poor root development that often appears aboveground as a stunted, yellow plant. In established alfalfa stands, aphanomyces can continue to infect roots, stunting plant growth and producing lower yields.
Aphanomyces can be found in many soils across the U.S. The oomycetes (which infect plants by mobile soil spores) are most active in soils that are saturated and poorly drained. Oftentimes, soil compaction and limited water dispersal will aggravate the disease symptoms. Spring planting conditions are typically wetter, providing a perfect environment for heightened aphanomyces infection. Multiple races have been identified in the Midwest, East and areas of the Pacific Northwest, including race 1, race 2 and more recently enhanced multirace.
Anthracnose
Anthracnose is a severe stem and crown fungal disease that causes defoliation and stem death. It appears as oval- to diamond-shaped lesions on the stem. These lesions are deep, destructive and disrupt nutrient and water movement in the plant. Infected stems often appear wilted and display the “shepherd’s hook” once the disease has killed the stem. Anthracnose infection can cause significant yield losses of up to 25% or more. Crowns from infected plants decline in productivity. Once infected, crown death is likely from this pathogen.
There are multiple races of anthracnose. Race 1, race 2 and recently race 5 have been identified to cause economic damage to alfalfa. Race 5 is a very 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 midsummer and fall. Anthracnose spores readily spread from stem to stem and plant to plant through wind, rain and harvesting equipment.
Advanced disease resistance packages
Protect the roots and stems of your alfalfa with advanced plant genetics. Both aphanomyces root rot and anthracnose can be important threats to protect your crop against. New varieties are available that offer disease resistance to multiple races of both aphanomyces root rot and anthracnose for protection both above and below ground.
More ways to support your alfalfa crop
For additional protection during seedling establishment, use coated alfalfa seed treated with two modes of fungicide seed treatment. Mefenoxam (Apron XL) with pyraclostrobin (Stamina) offered good plant protection to pythium seed rot and damping off as well as phytophthora root rot and aphanomyces root rot. Research is ongoing to provide the most advanced genetic resistances built into the variety as well as additional seed treatments that provide superior protection during germination.
Talk to your local alfalfa dealer to learn more about new varieties and seed treatments and how they could benefit your alfalfa acres.
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