New alfalfa varieties are constantly being introduced into the marketplace. The number of varieties available for low-elevation desert areas in Arizona in the non-dormant and very non-dormant class is about 46. New varieties are introduced each year and unbiased yield comparisons are helpful to the grower to base the decision of whether or not to sow a new variety. The study reported here is part of the on-going effort to evaluate alfalfa variety performance in Arizona. The data contained in this report are also available at http://www.ag.arizona.edu/~azalfalf/yield/2000/. A summary of small grain variety trials conducted by the University of Arizona can be found online at http://ag.arizona.edu/pubs/crops/az1267.pdf.

Five alfalfa varieties (CUF 101, SW 14, SW8210, Pioneer 5888, and a grower selection originating from CUF 101 and noted as Baldwin Select) that were planted in October, 1994, into large plots (0.75 acres) to obtain actual field harvest data production during the years of 1995-1997. Varietal hay yields were very similar in 1995 until mid summer, when area soil temperatures reached above 100°F at the four inch depth for a period of about 6 weeks. During the summer months Baldwin Select had significantly higher yields than other varieties tested. Statistical differences in accumulated hay yields were noted beginning in August 1995 and continued through 1997. Baldwin Select was the highest yielding variety each year, producing 8.4% more than CUF 101 during this time period, worth $247/acre more an acre than CUf 101. Alfalfa varieties were similar in relative feed value. Yellowing from Empoasca spp. leafhoppers was greatest during the 1995-1996 winter on varieties with fall dormancy ratings of 9 or greater. Weed infestations during late summer 1996 appear inversely correlated with fall dormancy class. All varieties of dormancy classes 8 and 9 were almost 100% infested with weeds during September 1997, although Baldwin Select had significantly less infestation. Differences in plant populations in late September 1997 also appear to be correlated with fall dormancy class.

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.

Twenty four alfalfa varieties with fall dormancy ratings of 8 or 9 were tested in a replicated small plot trial on a heavy clay loam soil on the Safford Agricultural Center. This was the second year of a new study. UC 331 had the highest yield for the year but CUF 101 had the highest average yield. Heat units with thresholds of 77° F and 40° F are included for each cutting in the study.

Nine alfalfa varieties, most not previously tested under field conditions in Arizona, were planted October 29, 1997 using the same setting on a Great Plains Solid Stand 13 End Wheel drill. Varieties differed in lbs. of seed/acre planted, ranging from 28.0 for CUF 101 to 21.3 for Alto. Five cuttings were obtained through August 1998. The variety Alto yielded the most hay in the first and fourth cuttings and had the highest total yield from the first five harvests. Varieties with fall dormancy class ratings of 8 usually had higher yields than varieties of dormancy 9 during the spring and early summer growing season, which was below normal in temperature, resulting in class 8 dormancies having the highest total yields thus far.

Fourteen alfalfa varieties with fall dormancy ratings from 6 to 9 were tested in replicated small plot trials on the Kibler farm in Stewart District northwest of Willcox. The leading variety after three years of testing was DeKalb 189 with a dry matter yield of 8 tons per acre. Heat units with temperature thresholds of 77 °F and 40 °F are given for each cutting.

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.

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Mounted ill. Bibliography: leaves 263-265.