The Use of Norflurazon (Zorial 5G) in Parker Valley Alfalfa for Purple Nutsedge Suppression in 1998-99

An experiment was conducted in 1998-99 to study the efficacy of spring (April 30, 1998 and March 4, 1999) applications of Zorial 5G (1, 1.5, 2, 2.5, and 3 lb a.i./A), Treflan TRIO (2 lb a.i./A), and Visor 2.SG (0.25 and 0.5 lb a.i./A) on purple nutsedge control in alfalfa. The second half of split Zorial 5G (1+1, 1.5+1.5, and 2 +1 lb a.i./A per year) and Treflan TRIO (2+2 lb a.i./A per year) treatments were made each summer (September 8 and June 22). Purple nutsedge suppression on May 27, 1998 increased linearly as the rate of Zorial 5G applied increased from 1.5 to 3 lb a.i./A. The degree of nutsedge suppression resulting from the initial spring Zorial 5G applications increased with time, reached a maximum on August 4, 1998 (52 to 72 %), and declined later in the fall. Split spring and summer applications of Zorial 5G at annual rates of 2 or 3 lb a.i./A provided good (80-88 %) purple nutsedge suppression in the fall of the first year of this study although the single spring applications of 2 or 3 lb a.i./A provided greater suppression in the spring and early summer. Similar to 1998, there was a slow increase in Zorial 5G efficacy on purple nutsedge during the spring of 1999 with the single spring 1.5 to 3 lb a.i./A Zorial 5G applications resulting in very good control (89-96 %) on June 22, 1999. The annual application rate of 1 lb a.i./A Zorial 5G resulted in only fair purple nutsedge control (at best 75 %) and was significantly worse than the other Zorial treatments. During June, July and August of 1999, there were no significant differences between treatments that received 1.5, 2, 2.5 or 3 lb a.i./A Zorial in a single spring application. In addition, there were no significant differences in purple nutsedge control between treatments that received greater than 1.5 lb a.i./A in a single spring application versus treatments that received split applications of Zorial 5G. Thus, the split 2 lb a.i./A Zorial SG treatment and the two split 3 lb a.i./A treatments were not significantly better than the single spring applications of 2 and 3 lb a.i./A, respectively, during the second year of this study. To date, single applications of Visor 2.5G at 0.25 and 0.5 lb a.i./A and the split Treflan TRIO treatment (2+2 lb a.i./A per year) have provided poor purple nutsedge suppression in 1998 (0-25 %) and 1999 (0-5 %)