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Title: Management of seedling damping-off of alfalfa

item BERG, LAURINE - University Of Minnesota
item Samac, Deborah - Debby

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 7/24/2015
Publication Date: 8/1/2015
Citation: Berg, L., Samac, D.A. 2015. Management of seedling damping-off of alfalfa. Forage Focus. August 2015. Page 16.

Interpretive Summary:

Technical Abstract: A vigorous and productive alfalfa stand starts with strong and uniform seedling establishment. Seed rot and seedling damping-off are a significant cause of poor stand establishment in wet soils. A number of organisms cause seed rot and seedling damping-off including several species of Pythium. As a first step toward developing alfalfa resistant to diseases of Pythium, we undertook a survey in five Minnesota soils with a higher than expected incidence of damping-off. Soil samples were collected from fields under alfalfa for at least three years after corn or soybean, and were cultured in the lab to isolate Pythium species. Eight species were recovered from diseased alfalfa seeds and seedlings. Only three, P. irregulare, P. ultimum, and P. sylvaticum proved to be pathogens of alfalfa. In addition, we obtained and tested 21 Pythium pathogens of corn and soybean for the ability to cause disease in alfalfa. Of those, seven proved capable of attacking all three crop plants. We assessed all of the alfalfa pathogens for sensitivity to Apron XL and Stamina in a petri plate test. The Stamina seed treatment was generally not effective against Pythium. Of the 16 strains tested, only one was sensitive to Stamina. Apron XL reduced the incidence of damping-off caused by the pathogens, but the level of protection varied considerably among and within species. Half of the strains tested had low or moderate sensitivity to the Apron XL seed treatment resulting in less than 50% of the seeds protected from disease. Developing resistance to Pythium diseases would improve alfalfa stand establishment and stand productivity.