|Behnken, Lisa -|
|Breitenbach, Fritz -|
Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: November 18, 2011
Publication Date: December 1, 2011
Citation: Samac, D.A., Behnken, L.M., Breitenbach, F. 2011. New strategies for managing leaf diseases of alfalfa. Forage Focus. December 2011. p. 7-8. Technical Abstract: Leaf diseases are a serious problem for alfalfa management in all areas where alfalfa is grown. Defoliation from leaf diseases has been measured from 3-71% depending on time of year, environmental conditions, age of the stand, and location. In addition to yield loss, foliar diseases can reduce forage quality and seed yields. This article describes promising new strategies for reducing the damage from foliar diseases. Although some cultivars have low-moderate resistance to individual leaf diseases, resistance to multiple foliar diseases is not available. In the case of severe leaf disease, the crop should be harvested early to reduce leaf loss and remove inoculum. Recently, the fungicide Headline (pyraclostrobin, BASF) was approved for use on alfalfa and is labeled for management of the primary leaf diseases of alfalfa. Currently, this is the only fungicide registered for use on alfalfa. A trial was conducted during the summer of 2011 at Waseca, MN, to evaluate the performance of Headline to control leaf diseases in alfalfa and measure the impact on yield and forage quality. For each of the three cuttings, treatment with Headline or Headline plus Warrior significantly reduced leaf spots and increased yield compared to the untreated control or the treatment with Warrior alone. Researchers have long known that glyphosate, the active ingredient in Roundup herbicide, has antifungal activity. With the development of Roundup Ready alfalfa varieties, in which plants take up and tolerate glyphosate, it is possible to test whether glyphosate can be used to reduce damage from foliar pathogens. In greenhouse experiments it was found that application of glyphosate at the recommended field application rate completely prevented alfalfa rust infection on 4-week-old plants inoculated with the fungus 3 days after glyphosate treatment. Also, complete control of rust was obtained when glyphosate was applied up to 10 days after rust spores, indicating that the herbicide also has curative activity. Although field trials are needed to confirm the results, these studies indicate that glyphosate could be used to help manage foliar diseases in Roundup Ready alfalfa.