Annual grasses such as wild barley and Mexican sprangletop are of economic concern to alfalfa growers in western Arizona. Thus, granular formulations of thiazopyr (Visor 2.5G), trifluralin (Treflan TR-I0), and norflurazon (Zorial 5G) herbicides were evaluated for annual grass control in an established alfalfa field in Mohave County when applied after the first hay cutting in early spring and prior to irrigation. Visor 2.5G was applied in spring 1998 and 1999 at application rates of 0.25, 0.38, and 0.5 lb a.i./acre. Treflan TR-10 was applied at 2.0 lb a.i./acre in early spring or in both early spring and late summer. Visor 2EC was applied at 0.5 lb a.i./acre in spring 1998 but was replaced with Zorial 5G at 2.0 lbs a.i./acre in spring 1999. In 1998, good wild barley control (81%) resulted from a spring application of Visor 2.5G at 0.50 lb a.i./acre. The Visor 2EC formulation at 0.5 lb a.i./acre provided poor weed control (40 %) due to the retention of herbicide on the alfalfa foliage and lack of incorporation into the soil by irrigation. In 1999, fair wild barley control (73 to 79 %) resulted from spring applications of Visor 2.5G at 0.50 lb a.i./acre and Zorial 5G at 2.0 lb a.i./acre. During summer 1998, good Mexican sprangletop control (83-93 %) resulted from Visor 2.5G applied at 0.38 and 0.50 lb a.i./acre and Treflan TR-10 applied in both spring and summer at 2.0 lb a.i./acre. No alfalfa phytotoxicity was observed at the rates applied in this study.

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 %).

Two experiments were conducted during 1997 -98 to study the use of norflurazon (Zorial 5G) for purple nutsedge control in alfalfa. In experiment 1, Zorial 5G was applied in spring 1996 and 1997 at application rates of 1.0, 1.5, 2.0, and 3.0 lb a.i./A. Split applications were made each summer in four of eight treatments for total annual Zorial 5G rates of 2.0, 3.0, and 4.0 lb a.i./A-year. In the fall of 1997, each plot was divided into two subplots. One set of subplots was disced twice and replanted with alfalfa. Alfalfa planted into these subplots was not affected by the residual soil concentrations of norflurazon. In the other set of undisturbed subplots, the residual soil concentrations of norflurazon continued to provide substantial suppression of purple nutsedge in 1998. However, by August 1998, the 3 lb a.i. /A -year rate only provided fair nutsedge suppression (51 %), while the 4 lb a. i. /A -year rate still provided satisfactory suppression (75 %). At rates of 2 lb a.i. /A-year or less, the residual effects of norflurazon declined to low levels in 1998 and did not keep purple nutsedge population levels from rebounding to pretreatment levels. In experiment 2, the efficacy of single spring (April 30) applications of Zorial 5G (norflurazon) at rates of 1.0, 1.5, 2.0, 2.5, and 3.0 lb a.i./A; of Treflan TR10 (trifluralin) at a rate of 2 lb a.i. /A, and of Visor 5G (thiazopyr) at rates of 0.25 and 0.50 lb a.i. /A were evaluated. As of August 4, 1998, purple nutsedge was the predominate weed species in this experiment. Zorial 5G applications at rates ranging from 1.5 to 3.0 lb a.i. /A provided moderate (57-68 %) purple nutsedge suppression. Rates above 1.5 lb a.i./A did not significantly improve purple nutsedge control suggesting that in new alfalfa stands, 1.5 lb a.i/A may be an appropriate rate for the first part of a split application. To date, single applications of Visor 5G at 0.25 and 0.50 lb a.i./A and Treflan TR-10 at 2 lb a.i./A have provided poor (17-33 %) purple nutsedge suppression.

The tolerance of seedling alfalfa to norflurazon applied at planting or 6, 14, or 20 weeks after planting was evaluated in Parker Valley in the spring of 1998. At each application date, rates of 0, 1.5, 2, 3, or 4 lbs a.i./A of norflurazon formulated as a 5% sand granule (Zorial 5G) were applied using a ground driven Valmar granule applicator. Zorial 5G at rates ranging from 1.5 to 4.0 lbs a.i./acre applied no earlier than 6 weeks after planting had no effect on alfalfa seedling emergence and stand establishment. These applications also did not reduce the fresh weight of foliage harvested on July 1, 1998. For effective spring and summer purple nutsedge control, the first spring application of Zorial 5G should not be any earlier than 14 weeks after planting alfalfa or late January which ever is later. In a newly planted alfalfa field prone to high purple nutsedge weed pressure, spring Zorial 5G application rates ranging from 1.5 to 2.0 lbs a.i. /acre should be considered.