Jan - June 2003 Glufosinate in Sugarbeet 29 Glufosinate Rates, Timings, and Additives for Weed Control in Glufosinate-Resistant Sugarbeet Corey J. Guza l ,2, Corey V. Ransom l , and Carol Mallory-Smith2 lOregon State University Malheur Experiment Station 595 Onion Ave, Ontario, OR 97914 20regon State University 107 Crop Science Bldg, Corvallis, OR 97330 ABSTRACT Two experiments were conducted to evaluate weed control with glufosinate in glufosinate-resistant sugarbeet. The first experiment evaluated glufosinate rate, application timing, and combinations with ammonium sulfate (AMS). The second experiment examined glufosinate alone and in combination with postemergence (POST) or preplant incorporated (PPI) ethofumesate. In the first experiment in 1998, increasing glufosinate rate improved common lambsquarters control and redroot pigweed control was greater when I glufosinate was initially applied mid-post (MP) compared to early-post (EP). In 1999, increasing glufosinate rate, beginning treatment at the EP application timing, and the addition of AMS, increased redroot pigweed contro l. Barnyardgrass control also was improved with the higher glufosinate rate and with the addition of AMS. Sugarbeet yield in 1998 was not significantly affected by glufosinate treatments. In 1999, the addition of AMS to low glufosinate rates and the addition of AMS to treatments applied beginning MP increased sugarbeet yield. In the second experiment, three applications of glufosinate and two applications of glufosinate following PPI ethofumesate resulted in weed control equal to a standard herbicide program consisting ofPPI ethofumesate followed by a premix of ethofumesate, desmedipham, and phenmedipham (1: 1: 1