• Evaluation of Planting Date Effects on Crop Growth and Yield for Upland and Pima Cotton, 1997

      Silvertooth, J. C.; Norton, E. R.; Brown, P. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Three field studies were conducted in 1997 at the Maricopa (1,175 ft. elevation) and Marana (1,974 ft. elevation Agricultural Centers to evaluate the effects of three planting dates on yield and crop development for three representative Upland varieties. Planting dates ranged from 13 March to 8 May and also 312-1159 HU/Jan 1 (86/55° F thresholds). Crop monitoring revealed increased vegetative growth tendencies with later plantings. General trends also showed decreasing lint yield with the later plantings for all varieties at each location.
    • Short Staple Regional Cotton Variety Trials, Graham County, 1997

      Clark, L. J.; Carpenter, E. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Two on farm, replicated short staple variety demonstrations were planted in 1997. Twelve varieties were evaluated on the Carpenter farm in Central and on the Colvin farm in Eden. Several new varieties were planted in both studies, including 2 transgenic varieties, DP 35B and BXN 47, 2 varieties from Australia and four other varieties seen for the first time. DP 35B and Stoneville 474 were the highest yielding varieties in Central and the Australian variety, IF 1003, had the highest yield in Eden with yields over 2 bales per acre. Other agronomic data from the varieties and 11111 values from the lint are also included in this report.
    • Evaluation of Irrigation Termination Affects on Upland Cotton, 1997

      Silvertooth, J. C.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      A single field study was conducted in 1997 at the Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of three dates of irrigation termination on the yield of a common Upland cotton variety (DP NuCOTN 33b). Planting date was 9 April (668 HU /Jan 1 86/55° F thresholds. Three dates of irrigation termination (IT1, IT2, and IT3) were imposed based upon crop development into cut -out. The earliest irrigation termination date, IT1 (7 August) was made as early as possible in an attempt to provide sufficient soil - water such that bolls set at the end of the first fruiting cycle would not be water stressed and could be fully matured. The second termination (IT2) date was 20 August, and provided one additional irrigation over IT1. The final (IT3) date was 17 September, which was staged so that soil moisture would be sufficient for development of bolls set up through the last week of September and provide full top-crop potential. Lint yield results revealed no differences among any of the IT treatments. Mirconaire values increased slightly with later IT dates.
    • Whitefly Management in Arizona: Contribution of Natural Enemies to Whitefly Mortality

      Naranjo, Steven E.; Ellsworth, Peter C.; Diehl, Jonathon W.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Direct-observation studies were conducted to identify causes and estimate rates of mortality of whiteflies over the course of four generations between late June to early September in replicated experimental plots. In plots receiving no whitefly insecticides. predation and dislodgment were major sources of egg and nymphal mortality and overall survival from egg to adult ranged from 1-8.5%. Similar patterns were observed in plots treated with insect growth regulators. except that Knack caused high levels of egg inviability and Applaud was a major source of mortality in small nymphs during the second generation immediately following single applications of these materials. Mortality due to predation was generally lowest for eggs and nymphs in plots treated with a rotation of conventional insecticides reflecting disruption of the predator fauna. Parasitism was a very minor source of mortality throughout. The selective action of the IGRs enhances the abundance and activity of natural enemies resulting in high levels of whitefly control with minimal use of disruptive insecticides. Natural enemies likely contribute to the "extended" residual effects of IGRs so commonly reported by growers.
    • Evaluation of a Feedback Approach to Nitrogen and Pix Applications, 1997

      Silvertooth, J. C.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      A single field experiment was conducted in 1997 at Marana, AZ to compare a scheduled approach (based on stage of growth) versus a feedback approach (based on growth parameters) to both nitrogen (N) and mepiquat chloride (P1X) applications on Upland cotton (Gossypium hirsutum L.). PIX feedback treatments were based upon fruit retention (FR) levels and height to node ratios (HNRs) with respect to established baselines for Arizona growing conditions. Scheduled and feedback FIX applications were made for a total of 0.75 and 1.50 pt./acre, respectively, with the scheduled treatments being initiated earlier in the fruiting cycle (early and peak bloom). Feedback PIX treatments consisted of a single 0.75 pt./acre application near peak bloom (approx. 2000 heat units after planting, HUAP, 86/55 °F threshold). Scheduled applications of fertilizer N totaled 150 lbs. N/acre from two applications and feedback N treatments received a total of 100 lbs. N/acre from two applications. Treatments consisted of all combinations of scheduled or feedback applications of both N and PIX. The highest lint yields were from treatments receiving PIX applications, with significant differences (P ≥ 0.05) between a check treatment (with no FIX applications) and several other treatments that did receive PIX applications. If FIX was applied, there were no significant differences between the scheduled or feedback approach. Applications of PIX in relation to increasing HNRs (feedback approach) are demonstrated and reinforced in this study.
    • Spatial Analysis of Aspergillus flabus S and L Strains

      Orum. T. V.; Bigelow, D. M.; Cotty, P. J.; Nelson, M. R.; Silvertooth, Jeff; Department of Plant Pathology, University of Arizona, Tucson, AZ; USDA/ARS/SRRC, New Orleans, LA (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      The distribution of S and L strains of Aspergillus flavus is more stable than previously realized. Analysis with GIS/geostatistics shows that patches of similar S strain incidence persist over years. This information will be exceptionally useful to programs involved with or planning large-scale treatments to reduce aflatoxin contamination because it can be used to spatially focus treatments.
    • Short Staple Variety Trial, Greenlee County, 1997

      Clark, Lee J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Six short staple cotton varieties including two New Mexico acalas varieties and one advanced strain, two Australian varieties and a SureGrow variety with higher yield potential were tested in this study. The SureGrow variety, SG 125 had the highest lint yield with a yield of 875 pounds of lint per acre, out producing the following varieties by 80 pounds per acre. The average yield was about 100 pounds per acre lower than the previous year, and 50 pounds less than the 5 year average due to a cold spring and an early frost. In addition to lint yields; percent lint, plant heights, height to node ratios, plant populations and lint hvi values are shown. A lint yield comparison for 1993 through 1997 is included in this paper.
    • New Insights Regarding Estimating Lygus Susceptibility to Insecticides

      Dennehy, T. J.; Russell, J. E.; Antilla, L.; Whitlow, M.; Silvertooth, Jeff; Extension Arthropod Resistance Management Laboratory; Department of Entomology, University of Arizona, Tucson, AZ; Arizona Cotton Research & Protection Council, Tempe, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Lygus susceptibility was found to vary widely from year to year, from region to region and, for some insecticides, even within the season. It is for this reason that producers need current, region-specific recommendations in order to determine which insecticides are most effective at their locale. Our studies were intended to improve understanding of the reliability of glass vial bioassays for estimating efficacy of insecticides used against lygus bugs. Results show that the standard glass vial method offers considerable promise for detecting differences in susceptibility of lygus to some, but not all, insecticides. However, mortality in vial bioassays did not serve as a reliable predictor of the relative toxicity of residues of five insecticides in field treatments. Therefore, field evaluations of insecticide efficacy continue to be essential for selecting the insecticides that provide the best control of lygus. Once the most effective materials are selected from field trial results, bioassays can be used to efficiently monitor changes in population susceptibility to these insecticides. Additional new insights provided by our studies are that efficacy of residues of insecticides declined rapidly, such that after three days all insecticides caused very little mortality to adult lygus bugs. Lastly, we found a marked difference between residual and direct contact toxicity of the five insecticides evaluated. Even the insecticide treatments that resulted in relatively low toxicity in residual exposure tests killed 95-100% of lygus bugs that they contacted directly under field conditions. This finding indicates that producers experiencing severe problems with lygus control would be well advised to improve insecticide coverage.
    • Lygus Chemical Control: Are Combinations Sprays Worth It?

      Ellsworth, Peter C.; Gibson, R.; Howell, D.; Husman, S.; Stedman, S.; Tickes, B.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      We need efficient sampling methods, appropriate thresholds based on a well -defined Lygus density yield relationship, and knowledge of the most effective chemical controls available. Insecticides were evaluated for control of Lygus at 5 'at risk' grower locations, as well as at 4 other experimental sites. Application methods were different at each site according to grower practice or experimental protocol (5-20 GPA; by ground, air, or electrostatically-assisted ground sprayers). Evaluations were made based on the number of Lygus per 100 sweeps. Orthene®, Vydate® or to a lesser degree, Monitor® used alone and at high rates appeared to perform adequately at all sites. Both rates of Regent™, a new chemistry under development by Rhône- Poulenc, provided excellent levels of control comparable to Orthene in a high density test. In this same test, none of the experimental and registered pyrethmids provided adequate control when used alone. Thiodan®, when mixed with Mustang®, provided some level of control. Over all tests measured for yield, a positive net return was possible with no more than 2 sprays of solo materials which yielded between 0.3 and 0.5 bales/A more than untreated comparisons or between $51-130/A net return. Also, at one site where yields were in excess of 4.2 bales/A, optimum planting and fruit-set prior to heavy Lygus pressures and monsoon-associated heat stress was an important cultural tactic for avoiding losses to Lygus - the check yielded over 3.7 bales /A! As seen at grower sites and confirmed in experimental studies, solo compounds, at appropriate rates, performed as well or better than any combination tested. And, mixtures at this time do not appear to provide any additive, synergistic or economic benefits in the control of Lygus. Combinations, unless indicated by another pest problem (e.g., whiteflies), are not "worth it," and needlessly expose the grower to larger input costs, "empty" applications, and higher risks of resistance, pest resurgence, secondary pest outbreaks, and phytotoxic effects by insecticides.
    • Do PIX® Application Guidelines Change for Bt Cotton?

      Husman, Stephen H.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Two PIX experiments were conducted on commercial cooperator sites in Waddell and Buckeye, Az in 1997 to evaluate the validity of the published University of Arizona (UA) PIX application guidelines for Bt cotton. Experimental treatments consisted of an untreated check, a calendar based application schedule (early bloom, peak bloom, cutout), and a feedback approach using plant growth measurements based on the UA PIX guidelines (height:node ratio, fruit retention). There were no significant yield differences at the Waddell site where height:node ratios and fruit retention values were above the optimum baseline season long, conditions not supportive of PIX applications. There was a significant yield decline at the Buckeye site between the untreated check and the calendar based treatment. Due to low plant vigor season long , there were no feedback based PIX applications. PIX applications under low vigor conditions can further compromise plant vigor and ultimately yield. The UA PIX application use guidelines are valid and should be used for both Bt and non -transgenic Upland cotton varieties.
    • Aflatoxin Contamination of Bt and Non-Bt Cottonseed

      Knowles, Tim C.; Wakimoto, Vic; Wakimoto, Del, 1947-; Keavy, Mike; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Transgenic Bt cotton varieties that are resistant to pink bollworm should sustain less feeding damage to bolls and cottonseed, compared to non-Bt varieties that are more susceptible to feeding damage by pink bollworm larvae. Prior to boll opening, the aflatoxin producing fungus Aspergillus flavus cannot penetrate undamaged cotton bolls. Thus resistance to pink bollworm could result in reduced aflatoxin contamination under high pink bollworm pressure. Cottonseed aflatoxin levels of Bt and non-Bt varieties were compared at various planting and harvest dates. Bt and non-Bt cotton varieties had similar cottonseed aflatoxin levels. Long season production systems favored high cottonseed aflatoxin levels, compared to short season production systems, regardles of the cotton variety grown.
    • Whitefly Management in Arizona: Looking at Whole Systems

      Ellsworth, P. C.; Naranjo, S. E.; Castle, S. J.; Hagler, J.; Henneberry, T. J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Whiteflies remain a threat to production of cotton in Arizona. Looking at a series of commercial-scale trials, levels last season were delayed compared to previous years, but at higher densities than in 1995, an outbreak year. Efforts must be expended to optimize insect growth regulator (IGR) use and integrate these tactics with other aspects of crop and pest management. Broad spectrum insecticide use prior to treatment for whiteflies with IGRs alters the ecology of the system. Whitefly densities consistently increased after disruption with a Lygus insecticide relative to Lygus -untreated areas. While Lygus control is a production imperative, guidelines are presented for minimizing the impact of this disruption. The modes of action for the two IGRs differ substantially and result in subtle changes in population age structure and dynamics. The consequences of these changes impact natural enemies and should be noted by producers when selecting an IGR or monitoring populations after treatment. Re- treatment after initial IGR sprays depends on many factors. While apparently similar levels of suppression are possible when only one IGR is used, regimes using both available IGRs resulted in the fewest number of damaging large nymphs late in the season, just prior to defoliation. Conventional insecticides rotated according to pre-IGR introduction guidelines (`95IRM') also suppressed populations significantly and comparably to IGR regimes until late in the season. Then, whitefly densities rose aggressively just prior to defoliation and pyrethroid susceptibility was significantly reduced in the 951RM regime. Full adoption of IGR -based technology along with `Bt' cotton allows growers to better manage whiteflies with fewer disruptions which can lead to secondary pest outbreaks, pest resurgence, and insecticide resistance.
    • Upland Regional Cotton Variety Test at the Maricopa Agricultural Center, 1997

      Hart, G. L.; Nelson, J. M.; Clark, L. J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Thirty four upland cotton varieties were grown at the Maricopa Agricultural Center as part of the national cotton variety testing program. Lint yield, boll size, lint percent, plant population and fiber property are presented in this paper.
    • Evaluation of a Nitrogen-15 Microplot Design in a Furrow Irrigated Row Crop System

      Silvertooth, J. C.; Navarro, J. C.; Norton, E. R.; Sanchez, C. A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Two field experiments were conducted in Arizona in at two locations, Maricopa in 1991 (Casa Grande sandy loam) and Marana (Pima clay loam) in 1995. The purposes of the experiments were to evaluate the dimensions of an ¹⁵N microplot design used in a furrow irrigated row crop system. The experiments each utilized ammonium sulfate fertilizer with 5 atom % ¹⁵N enrichment applied at a rate of 56 kg N/ha in simulated side-dress band application during the early bloom stage of development of Upland cotton (Gossvpium barbadense L). At each location, microplots were 4, 1.02 m rows wide and 1.00 m in length. Whole plant samples were collected at specific locations within and near the microplots. Uptake of ¹⁵N by plants was uniform within microplots but declined symmetrically in relation to microplot borders. Collection of plant materials within 25 cm of microplot borders provided uniform ¹⁵N enrichment levels for determining fertilizer N uptake and recovery. Use of microplots with the dimensions of those used in this study are sufficient for collecting plant materials from a 1 m² area; consisting of two, 50 cm segments from the interior two rows of the four row microplot. This also allows for sufficient distance from the perimeter of the microplot to account for border effects.
    • Efficacy of Experimental Insecticides for Whitefly Control in Cotton, 1996

      Kerns, David L.; Tellez, Tony; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Experimental insecticides were evaluated for control of sweet potato whiteflies relative to a commercial standard in cotton. Ni-25 provided excellent whitefly control and was equivalent to the commercial standard (Knack followed by Danitol + Orthene). Fenoxycarb + pymetrozine provided goodwhitefly control but seemed to require 2 sequential applications before control was equivalent to Ni-25. Diofenolan + pymetrozine appeared to be a slightly weaker treatment, but still provided acceptable whitefly control.
    • 1997 Season Update on Resistance of Arizona Whiteflies to Synergized Pyrethroid and Select Non-Pyrethroid Insecticides

      Dennehy, Timothy J.; Williams, Livey III; Li, Xiaohua; Wigert, Monika; Silvertooth, Jeff; Department of Entomology, The University of Arizona; Extension Arthropod Resistance Management Laboratory, Tucson, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      A whitefly resistance crisis in Arizona in 1995 prompted the development of a resistance management strategy in 1996 that recommended maximal once per season use of two insect growth regulators, pyriproxyfen (Knack®) and buprofezin (Applaud®), and limited and delayed use of synergized pyrethroid insecticides in cotton. Statewide monitoring of whitefly resistance has shown that implementation of this strategy has substantially reduced whitefly resistance to the synergized pyrethroids and has also resulted in increased susceptibility to key non pyrethroid insecticides. Having benefited from two years of success with this strategy, the Arizona cotton industry now faces the question of whether it can be sustained as pyriproxyfen and buprofezin gain additional registrations for use against whiteflies in vegetables, melons and glasshouse crops.
    • Infection of Sorghum Varieties by the Cotton Root-knot Nematode, Meloidogyne incognita

      McClure, M.; Husman, S.; Schmitt, M.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Twentythree varieties of sorghum, Sorghum bicolor, were evaluated for susceptibility to the cotton root -knot nematode, Meloidogyne incognita race 3. Eggs per gram of root were used as a measure of nematode reproduction and host susceptibility. The nematode reproduced on all varieties tested Mean egg counts were lowest on the varieties Northrup King (NK) KS-737, MF.; NK 1580,M; NK Ks-735 M.F.; NK 714Y MF.; NK Lt. Bronze X 609 M; Ciba-NK C-1506, M; and Pioneer 8877, but these varieties are still considered to be hosts capable of sustaining or increasing nematode populations in cotton fields. All varieties were better hosts than cotton.
    • Marana Pima Test, 1997

      Hart, G. L.; Nelson, J. M.; Barney, Glen; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Nine pima cotton varieties were grown at Marana Agricultural Center as part of the national cotton variety testing program. Lint yield, boll size, lint percent, and plant population are presented in this report.
    • Whitefly Management in Arizona: Conservation of Natural Enemies Relative to Insecticide Regime

      Naranjo, Steven E.; Hagler, James R.; Ellsworth, Peter C.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Field studies were conducted in 1997 to evaluate strategies for management of whitefly (Bemisia tabaci). We evaluated the effects of different insecticide regimes (conventional and insect growth regulators [IGR]) on the abundance of native parasitoids and predators associated with whitefly in Arizona cotton. Immature parasitoids were most abundant in untreated control plots and there was little difference among insecticide regimes. Percentage parasitism was low overall (< 30 %), but was highest in Knack plots and lowest in untreated control and Applaud plots. Predator populations were lowest in plots treated with conventional insecticides, and there were several instances where weekly or season -long populations of several predator species/groups were slightly depressed in IGR plots compared with the untreated check. Overall, results are encouraging and indicate that use of IGRs helps to conserve populations of native natural enemies.
    • Cotton Defoliation Evaluations, 1997

      Silvertooth, J. C.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Three field experiments were conducted near Yuma, Coolidge, and Marana, AZ in 1997 to evaluate the effectiveness of a number of defoliation treatments on Upland (var. DP NuCotn 33b) cotton. All treatments consisted of materials commercially available in Arizona. Results reinforce general recommendations regarding the use of low rates (relative to the label ranges) under warm weather conditions and increasing rates as temperatures cool.