• Making Late Season Decisions to Terminate Insecticide Use Against Lygus

      Ellsworth, Peter C.; Barkley, Virginia; Department of Entomology & Maricopa Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      The focus of our 2002 field study was to answer a fundamental question in insect control. Once spraying has begun for a particular pest, when should it stop? In this case, we are faced with the question of when to discontinue sprays for Lygus hesperus in cotton. Cotton is susceptible to Lygus any time there are productive squares on the plant. This study developed a series of worst-case scenarios in which to provide information on timing of the latest possible sprays of economic benefit. By late planting (30 May) varieties from three different maturity groups, we were able to examine Lygus control dynamics just prior to, at, and after cutout — initiation of cut-out was defined as NAWF = 5. We found large differences in yield among the four Lygus chemical termination (LT) treatments. The earliest termination (LT1, 2 weeks prior to cut-out) suffered the largest losses to Lygus, ca. 20–50% of the maximum yield. Conversely, extending Lygus chemical control 1–3 weeks after cut-out (LT3 & LT4) provided no yield benefit whatsoever, regardless of the variety examined. Maximum yields and maximum profits were gained in the LT2, where Lygus controls were continued up to 1 week prior to cutout. Given that there was only 1 week separating the LT1 and LT2 timings, it is clear that timing is absolutely critical. The timing used in this study corresponds with previously established threshold guidelines; treat when there are at least 15 total Lygus with at least 4 nymphs per 100 sweeps. Levels far exceeded this threshold late in the season, yet additional chemical controls after cut-out provided no additional yield or control benefits. Further, we have confirmed that nymphs are the life stage of major concern with, by far, the most capacity to reduce yields. Nymphal reductions were well-correlated with yield enhancement. The best timing (LT2) achieved ca. 93% reduction in nymphal densities during the critical 3- week period around cut-out. In contrast, adult numbers were reduced by only 16% during the same period. These results establish an upper bound for treatment of Lygus, no later than 1 week prior to cut-out; however, more work is necessary to identify if earlier cessation is possible under more normal planting conditions.
    • Phosphorus Fertility Evaluation in Graham County

      Norton, E. R.; Clark, L. J. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      A field study was implemented in 2002 in the Upper Gila River Valley of Safford to investigate the effects of varying phosphorus (P) fertilization rates on yield and quality of Upland cotton. This study is a continuation of work performed in this valley that began in 1998. This study was organized in a randomized complete block design with four treatments including four rates of 10-34-0 fertilizer, 0, 15, 30, and 45 gallons per acre (gpa) replicated 4 times. Lint yield results indicate a positive response to the application of 10-34-0 fertilizer with yield increasing linearly up to 30 gpa. The 45 gpa treatment resulted in a slightly lower yield than the 30 gpa treatment. This was likely due to the high level of nitrogen (N) fertilizer and excessive vegetative growth at the expense of reproductive growth (yield) that occurred in treatment 4.
    • Pima Cotton Regional Variety Trial, Safford Agricultural Center, 2002

      Clark, L. J.; Carpenger, E. W.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Twenty long staple varieties were tested in a replicated small plot trial on the Safford Agricultural Center in Graham County at an elevation of 2950 feet. The highest yielding variety in this study was HA 195 with a yield of 1419 pounds of lint per acre. This interspecific hybrid was the highest yielding variety in the 2001 study also (1). DP 340, one of Olvey’s varieties, was the highest yielding non-hybrid variety in the study; it yielded over 1200 pounds of lint per acre. Yield and other agronomic data as well as fiber quality data are contained in this paper along with estimated values of the lint.
    • Plant Population Effect on Yield and Fiber Quality of Three Upland Cotton Varieties at Maricopa Agricultural Center, 2002

      Galadima, A.; Husman, S. H.; Silvertooth, J. C. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      A field experiment was conducted at the University of Arizona Maricopa Agricultural Center (MAC – 1100 ft. elevation) in 2002 to evaluate plant population relationships with conventional row spacing under a range of high population conditions with new Upland cotton (Gossypium hirsutum L.) varieties. The varieties, which included AG3601, DP458BR, and STV4892BR, were each planted to six densities of 15,000, 30,000, 45,000, 60,000, 75,000, and 90,000. Inseason plant measurement data revealed crop vigor and fruit retention levels were well within the optimum threshold for all varieties and populations. There was no interaction between variety and population in terms of lint yield and fiber quality parameters. However, results show significant differences in lint yield and fiber strength among varieties but not the fiber micronaire. In addition, higher population had no significant effect on lint yield or fiber quality. Higher populations had no effect in lowering fiber micronaire to premium levels as well.
    • Reduced Tillage Effects on Irrigation Management in Cotton

      Martin, E. C.; Adu-Tutu, K. O.; McCloskey, W. B.; Husman, S. H.; Clay, P.; Ottman, M.; University of Arizona, Tucson, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Conservation or reduced tillage practices in cotton-based crop rotation systems were studied in field experiments initiated at Marana, Coolidge and Goodyear in 2001. Following barley cover and grain crops, soil and water management assessments were made during the 2002 cotton season at the three sites. Cover and grain crop residues and a lack of tillage prior to planting cotton or during the cotton season increased the infiltration of irrigation water into coarsetextured soils, slowed irrigation advance times, and increased the amount of irrigation water used at two of the three sites compared to conventional tillage treatments.
    • Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2002

      Silvertooth, J. C.; Galadima, A.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Field experiments investigating N fertilizer management in irrigated cotton production have been conducted for the past 15 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2002, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar at the MAC and MAR locations. Trends associated with residual fertilizer N effects are not evident at either location just two seasons following N fertilizer applications.
    • Review of the 2002 Arizona Cotton Season

      Silvertooth, Jeffrey C. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
    • Short Staple Variety Trial in Cochise County, 2002

      Clark, L. J.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Twelve varieties were tested including two New Mexico Acalas, two California Acalas from CPCSD, the new Arizona Cotton Grower’s variety and seven other upland varieties. Among the twelve varieties, eight contained the roundup resistant gene, which is very important for the high elevation trials. Four of these roundup resistant varieties were stacked gene varieties also containing the Bollgard trait. The highest yielding variety in the trial was 1517-99, with a yield approaching 800 pounds of lint per acre. This yield was lower than seen in 2001. In addition to the plant mapping data and HVI data which are provided, estimates of the crop values are also included in this report.
    • Short Staple Variety Trial in Virden, NM, 2002

      Clark, L. J.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Twelve varieties were tested including two new herbicide resistant entries from California, Riata and Nova, two New Mexico Acalas, seven roundup resistant entries from Delta and Pine Land Co., Stoneville, SureGrow and FiberMax, and the new variety developed for the Arizona Cotton Grower’s Association, AG 3601. The highest yielding variety in the trial was FM 989 with a yield of 1045 pounds of lint per acre. It was also the highest yielding variety at this location last year. The Acala 1517-99 placed second in yield at 1039 pounds of lint per acre. HVI data are also included in this report.
    • Susceptibility of Arizona Pink Bollworm to Cry1Ac Following Six Years of Intensive Use of Transgenic Bt Cotton in Arizona

      Denney, Timothy J.; Shriver, Laura; Sims, Maria A.; Holley, Danny; Carrière, Yves; Tabashnik, Bruce; Antilla, Larry; Whitlow, Mike; Department of Entomology, The University of Arizona, Tucson, AZ; Arizona Cotton Research and Protection Council, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      We summarize information on the performance of Bt cotton against pink bollworm (PBW), Pectinophora gossypiella, in Arizona following six years of use of this new technology. Monitoring of PBW susceptibility to Bt toxin Cry1Ac was conducted annually since 1997 by collecting insects from ten to 17 cotton fields, culturing strains in the laboratory, and measuring susceptibility to Cry1Ac in diet-incorporation bioassays. Based on survival in discriminating concentration bioassays of 10 μg Cry1Ac/ml of insect diet, resistant PBW were detected in low frequencies at 10 out of 17 Arizona locations sampled in 2001 and ranged from 0.0 to 4.0%. Though significantly more abundant than in the previous three seasons, resistant PBW were statistically less abundant in 2001 than they were in 1997. One collection from Paloma, AZ, had 4.0% survivors (uncorrected, actual survival) in bioassays of 10 μg/ml and samples from Coolidge, Maricopa, and Parker Arizona yielded • 1.0% survivors of this concentration. Susceptibility of a limited numbers of 2001 collections of PBW from California, New Mexico and Texas is also reported. Bioassays of 2002 collections are underway at the time of this writing. In a parallel effort, field efficacy of Bt cotton against PBW was documented at five to 39 Arizona locations per year since 1995 by collecting cotton bolls at seasons’ end and counting PBW and exit holes. In 39 pairs of adjacent Bt and non-Bt fields evaluated in 2001 by the Arizona Cotton Research and Protection Council, mean end-of-season pink bollworm infestation levels were > 15% for non-Bt fields and were < 0.15% in adjacent Bt fields. Thus, field observations indicated that performance of Bt cotton continued to be excellent throughout Arizona in the 2002 season.
    • Twin-Line Per Bed Plant Population and Variety Evaluation

      Husman, Stephen H.; McCloskey, Wililam B.; White, Kyrene (College of Agriculture, University of Arizona (Tucson, AZ), 2003-05)
      Two experiments were conducted at the University of Arizona Maricopa Agricultural Center in 2002 designed to evaluate cotton yield and fiber quality at various plant populations and to test cotton variety performance in a twinline per bed cotton production system. The plant population experiment consisted of four target populations which included 60, 80, 100, and 120,000 plants per acre (PPA) and two varieties, Stoneville 4892BR and AG3601. The resulting plant populations were 52800, 69200, 82800 and 96200 for ST4892BR and 54800, 70800, 90500 and 104500 for AG3601. The two lowest plant populations resulted in the highest lint yields for both varieties and were similar but there was a significant linear of decreasing yield with increasing plant population. The highest lint yields in the twin line variety experiment were DP449BR (1743 lb/acre) and DP5415R (1702 lb/acre) which were not statistically different.