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Title: Evaluating Headline fungicide on alfalfa production and sensitivity of pathogens to pyraclostrobin

Author
item Samac, Deborah - Debby
item HALFMAN, BILL - University Of Wisconsin
item JENSEN, BRYAN - University Of Wisconsin
item BRIETENBACH, FRITZ - University Of Minnesota
item BEHNKEN, LISA - University Of Minnesota
item Willbur, Jaime
item UNDERSANDER, DANIEL - University Of Wisconsin
item BLONDE, GREG - University Of Wisconsin
item Lamb, Joann

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2013
Publication Date: 9/17/2013
Publication URL: http://handle.nal.usda.gov/10113/57953
Citation: Samac, D.A., Halfman, B., Jensen, B., Brietenbach, F., Behnken, L., Willbur, J.F., Undersander, D., Blonde, G., Lamb, J.F. 2013. Evaluating Headline fungicide on alfalfa production and sensitivity of pathogens to pyraclostrobin. Plant Health Progress. DOI: 10.1094/PHP-2013-0917-01-RS.

Interpretive Summary: The recent high value of alfalfa hay has prompted a re-evaluation of crop management strategies that maximize yield and forage quality and provide a net positive return on investment. Leaf spot diseases reduce plant growth and development, which reduces yield, and cause premature defoliation, which reduces forage quality. Recently, the fungicide Headline was registered for use on alfalfa but information on disease control and return on investment is needed. Field experiments conducted in Wisconsin and Minnesota in 2012 found that Headline reduced defoliation in 12 out of 14 harvests and increased forage yield and return on investment in 5 out 12 harvests compared to the untreated control. Headline plus the insecticide Warrior II reduced defoliation in 10 out of 14 harvests and increased yield and return on investment in four harvests compared to Warrior II alone. The results indicate that fungicide application can increase yields under higher disease pressure and increase forage quality when the crop is harvested at later developmental stages, giving growers new options for controlling foliar diseases and maximizing yields.

Technical Abstract: Headline fungicide was recently registered for management of foliar diseases on alfalfa. The effect of disease control on yield, forage quality, and potential return on investment for fungicide application was determined for field experiments conducted at five locations in 2012, three in Wisconsin and two in Minnesota. Headline reduced defoliation in 12 out of 14 harvests and increased forage yield and return on investment in 5 out 12 harvests compared to the untreated control. Headline plus the insecticide Warrior II reduced defoliation in 10 out of 14 harvests and increased yield and return on investment in four harvests compared to Warrior II alone. Two common foliar pathogens were highly sensitive to pyraclostrobin, the active ingredient in Headline, with an in vitro EC50= 2.3 ng/ml for Phoma medicaginis and an EC50= 52 ng/ml for Stemphylium globuliferum. The results indicate that fungicide application can increase yields under higher disease pressure and increase crude protein when the crop is harvested at later developmental stages.