Submitted to: Western Society of Weed Science Research Reports
Publication Type: Research Notes
Publication Acceptance Date: 12/1/2006
Publication Date: 7/7/2007
Citation: Boydston, R.A. and Walsh, D. 2007. Prickly lettuce control in alfalfa seed production. Western Society of Weed Science Research Reports. Pg 70.
Technical Abstract: Weeds are particularly troublesome in alfalfa grown for seed due to the wider row spacing and the lack of multiple cuttings compared to alfalfa grown for hay. Prickly lettuce is often an escape weed in alfalfa seed production fields as it can germinate throughout the entire year and is naturally tolerant to several common herbicides used. A trial was initiated in the fall of 2005 to evaluate prickly lettuce control in alfalfa seed production with several herbicide treatments applied in the fall and spring to dormant alfalfa. The trial was conducted on a sprinkler irrigated alfalfa seed field near Touchet, WA. Prickly lettuce was 1 inch diameter with 1 to 2 leaves at the time of the fall herbicide applications and 1.5 to 3 inch diameter with 3 to 5 leaves at the time of the spring applications. Flumioxazin was applied at 0.125 and 0.25 lb ai/acre, diuron at 1.5 lb ai/acre, and norflurazon at 1.5 lb ai/acre. All treatments included paraquat at 0.5 lb ai/acre and nonionic surfactant at 0.25% (v/v) spray solution. In mid December, paraquat plus flumioxazin and paraquat plus norflurazon fall treatments controlled prickly lettuce 97 to 99%, whereas the paraquat plus diuron treatment controlled prickly lettuce 90%. By February 7, 2006 all fall applied herbicide treatments had totally eliminated prickly lettuce. Prickly lettuce control from all fall applied herbicide treatments was 99 to 100% in April and June. Prickly lettuce control from spring applied diuron plus paraquat or flumioxazin plus paraquat was 98 to 99%, whereas norflurazon plus paraquat controlled prickly lettuce 94%. Little or no alfalfa injury was noted in April and June from all herbicide treatments tested. Alfalfa seed yield was not significantly different among all treatments containing flumioxazin compared to the standard diuron plus paraquat treatment applied in the fall. Flumioxazin controlled prickly lettuce well without significantly injuring alfalfa and is being considered for labeling in alfalfa seed production.