| Abstract/Contents: | "Annual ryegrass, Lolium multiflorum Lam., is widely grown in the Coastal Plain of north Louisiana for forage production on cool-season temporary pastures. In many pastures, competition from yellow nutsedge, Cyperus esculentus, infestation has inhibited the productivity potential of annual ryegrass plantings. Because information was limited on the use of AC262,222 for yellow nutsedge control in cool-season temporary pastures, a herbicide experiment was conducted on a Bowie fine sandy loam soil that had been managed 20 years for annual ryegrass pasture. Herbicide treatments including rates of AC262,222 at 0 (control), .03, .06, .09, .12, and .15 lb ai in 10 gal diluent (H₂O) containing .25% non-ionic surfactant were broadcast on 7 June to a vegetative, yellow nutsedge stand. Stand density of yellow nutsedge was 77 culms/ft² with culms varying from slender 4-inch to robust 20-inch height. Phytotoxicity ratings made at 20 and 40 day intervals after application of treatments showed maximum (P<0.05) postemergence control of yellow nutsedge at 70% and 90%, respectively, where .03 lb AC262,222/A was applied. On 29 July, yellow nutsedge tubers were harvested from each treatment. The number of harvested tubers/ft² was not different (P>0.05) among treatments and averaged 38 tubers/ft² across treatments. Tuber germination, however, was affected by treatment. Following a 40-day germination period, maximum (P<0.05) control, 47%, occurred where .15 lb AC262,222/A had been applied. Thereafter, the effects of AC262,222 rates applied in June on preemergence control of yellow nutsedge in a fall planting of Marshall annual ryegrass were evaluated. Experimental plots were disked twice, harrowed, cultipacked, and top-dressed with fertilizer 6-16-39 at 500 lb/A prior to planting the ryegrass on 29 September in 7 rows spaced 7 inches at 30 lb/A in the center of each plot. On 8 November, emerged yellow nutsedge culms/ft² of plot were determined across treatments. When compared with that of the control, preemergence yellow nutsedge control optimized at 99.7%, where .03 lb AC262,222/A had been applied. Unfortunately, Marshall ryegrass exhibited a very low degree of tolerance to AC262,222 irrespective of previous use rate. Growth response by 15 December was 60% lower (P<0.05) than that for the control where .03 lb AC262,222/A had been applied; 90% lower for rates higher than .03 lb AC262,222/A. Over all, data indicated that: a) use of AC262,222 at .03 lb ai/A in June provided an optimum degree of postemergence yellow nutsedge control in a cool-season temporary pasture; and b) an annual ryegrass crop failure would occur when September plantings were made in areas that received AC262,222 treatment." |
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