Tuesday, November 14, 2006 - 12:30 PM

Yield and Composition of Roundup-Ready Alfalfa in Idaho.

Glenn Shewmaker and Don Morishita. Univ. of Idaho, Evergreen Bldg. 315 Falls Ave, Twin Falls, ID 83303-1827

The objective was to evaluate four herbicide treatments on Roundup Ready® (RR) alfalfa yield, forage quality, crop injury, and weed control.  A variety of RR alfalfa was established near Kimberly, Idaho on May 26, 2005.  Treatments were: 1) an untreated check, 2) glyphosate [Roundup WeatherMax, 21.3 fl oz/a], 3) glyphosate [Roundup WeatherMax, 42.7 fl oz/a], 4) imazamox [Raptor 6 fl oz/a; Crop Oil Conc. 1% v/v; Bronc 2.5% v/v], and 5) 2,4-DB-sethoxydim [Butyrac 200 3 qt/a; Poast 2.5 pt/a; Crop Oil Conc. 2 pt/a].  Herbicide treatments were applied 11 July and first cut harvested 25 July, 2005.  First cutting alfalfa yields taken at bud stage on 20 July were 450 kg dry matter per ha and were not significantly different for check, both glyphosate, and imazamox treatments but the 2,4-DB treatment produced a lower yield of 270 kg/ha in first cutting.  The combination of crop oil concentrate and the Butyrac 200-Poast caused a significant leaf burn on the alfalfa when the maximum temperature 1 d after treatment was 36 C.  This effect carried forward into second cutting, but yields were not significantly different for any treatments.  The total alfalfa dry matter yield averaged 1.6 MG/ha for the seedling year.  Glyphosate and imazamox treatments reduced the weed composition of the forage to about 10%.  This would be acceptable as dairy quality hay where the check (35% weeds) and 2,4-DB (46% weeds) treatments may have been less marketable.