ARS | Publication request: Alfalfa and weed response to alternatives to burning and new herbicides

Submitted to: Proceedings of the Northwest Alfalfa Seed Growers Association
Publication Type: Proceedings
Publication Acceptance Date: December 15, 2009
Publication Date: January 17, 2010
Citation: Walsh, D., Boydston, R.A. 2010. Alfalfa and weed response to alternatives to burning and new herbicides. Proc. 2010 Western Alfalfa Seed Growers Assoc.Winter Seed Conference. Las Vegas, NV. Pp. 55-88. Available http://ipm.wsu.edu/field/pdf/SeedSchoolReport2008_2009.pdf

Technical Abstract: Field burning of crop residues is a common practice in alfalfa seed production to reduce insect, disease and weed pests. A field trial was conducted to evaluate alternative crop residue management practices including mowing and shallow tillage. Field buring reduce seed viability prickly lettuce, mayweed chamomile, and Western salsify seed located on the soil surface by 99, 99, and 95%, respectively, but had no effect on seed buried 2.5 cm deep. Western salsify density was significantly affected by residue management. In mowed and no residue removal treatments (no tillage or burning) and no herbicide, salsify density ranged from 64 to112 plants/m2. Western salsify density was lowest in the burn and tillage treatments and was further reduced by herbicide treatment, although control was never complete. Burning followed by simazine treatment reduced salsify density to 3.8 plants/m2. In a second field tral, prickly lettuce and mayweed control were excellent with Chateau, Spartan, Asulox plus Sencor, and indaziflam applied PRE. Pyroxasulfone applied PRE only partially controlled prickly lettuce. Firstrate, Asulox plus 2,4-DB, Asulox plus Buctril, Asulox plus Basagran, and Asulox plus Raptor applied POST all controlled prickly lettuce 98% or more in late April. Harmony and Raptor applied POST only partially controlled prickly lettuce. All POST treatments except flumiclorac controlled mayweed chamomile greater than 89%. Alfalfa was not significantly injured by any PRE herbicide treatments. Harmony applied POST injured alfalfa the greatest, averaging 70% in late April and causing stunted and chlorotic growth, which eventually recovered. Firstrate and Resource applied POST caused temporary injury to alfalfa for several weeks after application. Other herbicide treatments applied POST did not injure alfalfa appreciably. Alfalfa seed yield was not significantly different among herbicide treatments . Percent alfalfa seed germination averaged 81% and did not differ among five POST applied treatments tested; Firstrate, Raptor, Asulox, Asulox+Raptor, and Gramoxone.