• Arizona's Multi-agency Resistance Management Program for Bt Cotton: Sustaining the Susceptibility of Pink Bollworm

      Sims, Maria A.; Dennehy, Timothy J.; Patin, Amanda; Carrière, Yves; Liu, Yong-Biao; Tabashnik, Bruce; Antilla, Larry; Whitlow, Mike; Silvertooth, Jeff; Department of Entomology, The University of Arizona, Tucson, AZ; et al. (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Bt cotton has been used in Arizona since 1996 with exceptionally positive results in terms of economic returns to growers and reductions in insecticide use in cotton. Yet, the isolation of pink bollworm highly resistant to Bt cotton from collections made in Arizona in 1997 demonstrated the seriousness of the threat that resistance poses to transgenic Bt technology. For this reason unparalleled measures have been taken to detect and manage resistance of pink bollworm to Bt cotton in Arizona. This paper presents results of statewide monitoring of pink bollworm susceptibility to the Bt toxin, Cry1Ac, conducted from 1997 to 1999. Mean susceptibility of Arizona pink bollworm to Cry1Ac increased from 1997 to 1999. Mean corrected mortality in 1μg/ml Cry1Ac assays was 52.3% in 1997, 90.6% in 1998, and 97.9% in 1999. Mean corrected mortality in bioassays of 10 μg/ml was 94.5% in 1997, 99.8% in 1998, and 100% in 1999. Selection with Cry1Ac in the laboratory has produced from 1997 field collections a strain possessing 200 to 900-fold resistance to Cry1Ac. This resistant strain is capable of surviving on Bt cotton. We provide an overview of other components of the multi-agency collaboration to sustain efficacy of Bt cotton in Arizona. These include: 1) evaluation of the field performance of Bt cotton; 2) mapping and analysis of use of Bt and non-Bt cotton and compliance with refuge requirements; 3) effectiveness of internal versus external refuges and movement of pink bollworm moths from refuges; and 4) activities of the Arizona Bt Cotton Working Group to formulate and implement effective resistance management strategies.
    • Insecticide Evaluation Studies, Safford Agricultural Center, 1999-2000

      Clark, L. J.; Carpenter, E. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Three studies were conducted over the two year period to explore the effectiveness of using pyrethroid insecticides only vs. rotating insecticide chemistries between the pyrethroids and organophosphates on both long and short staple cotton varieties. These same treatments were also evaluated over Bt and non-Bt varieties. In the worst case scenario, where weather conditions prevented timely application of insecticides and effectiveness of insecticides applied, long staple cotton yielded around 1/3 bale per acre after six insecticide applications. Within 200 feet of this experiment, during the same cropping season, with the same insecticides applied, DP 90B (a Bt variety) produced 3 bales per acre. Details of these studies are contained in this report.
    • Evaluation of a Drip Vs. Furrow Irrigated Cotton Production System

      Norton, E. R.; Silvertooth, J. C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      A newly installed subsurface drip system was compared to a conventional furrow-irrigated cotton production system in the Marana Valley in 2000. Regular measurements included soil moisture, flower tagging, general plant growth and development measurements, and lint yield. Results indicate that an increase in lint yield of approximately 250 lbs. lint/acre was obtained under the drip irrigation system. Approximately 1/3 less irrigation water was used under the drip irrigation system. Pounds of lint produced per acre-inch of water applied provide the most dramatic results. In the furrow-irrigated system approximately 25 lbs. of lint was produced per inch of water applied while the drip system ranged from 70-80.
    • Cotton Aphid Biology and Honydew Production

      Henneberry, T. J.; Forlow Jech, L.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Cotton aphid, Aphis gossypii Glover, fecundity, nymph development and honeydew production were studied in the laboratory. Apterous adult females produced an average of 1.7 nymphs per day and the nymphs (four instars) developed to adults in an average of 4.1 days at 26.7° C in the laboratory. Average longevity of adults was 16.1 days. More honeydew drops were produced by one-day old nymphs than three- or four-day old nymphs. Numbers of honeydew drops produced on a day to day basis were highly variable and did not show a distinct pattern of production. More honeydew drops, sugars and progeny were produced by adults at 26.7° C compared with 15.6 or 32.2° C. Increasing times of exposure of clean cotton lint to aphids and the resulting increasing amounts of honeydew sugars under laboratory and field conditions were significantly related to increasing cotton lint stickiness as measured with a thermodetector.
    • Soil Amendment Study on Long and Short Staple Cotton, Safford Agriculture Center, 2000

      Clark, L. J.; Carpenter, E. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Two soil amendments, Agriblend Plus and Superfloc A-836, were applied to cotton beds prior to planting at rates of 5, 10, 15 and 20 pounds per acre, incorporated and planted to short staple (DP 655BR) or long staple (HTO) cotton. The experimental plots were fertilized, irrigated and managed in a manner to produce optimal cotton yields. No statistically significant yield increases were seen from any of the treatments, even though a few interesting trends were observed. The report contains observations on plant mapping and lint quality data, in addition to yield data.
    • Effects of High Frequency Irrigation on Irrigation Uniformity III

      Martin, E. C.; Laine, G.; Sheedy, M.; Silvertooth, Jeff; University of Arizona, Cooperative Extension (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Data was collected for a third season to determine the effects of high frequency irrigation on irrigation uniformity in cotton production. The past two seasons indicated that high frequency irrigation worked better on sandier soils than soils containing high clay contents. Although no significant differences were found, higher yields were obtained on a site with a relatively high sand content. A field located at the Maricopa Agricultural Center was split into two treatments. Treatment 1 was irrigated at approximately 35% depletion of available water in the plant rootzone. Treatment 2 was irrigated at approximately 50% depletion in the crop rootzone. Although the yield data from Treatment 1 was higher on the average, statistically, there was no difference between the two treatments.
    • Planting Date Effects Crop Growth and Yield of Several Varieties of Cotton, Marana 2000

      Silvertooth, J. C.; Galadima, A.; Norton, E. R.; Moser, H.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      A field study was conducted in 2000 at the University of Arizona Marana Agricultural Center (1,974 ft. elevation) to evaluate the effects of three planting dates on yield and crop development of 13 varieties of upland cotton. Planting dates included 4 April, 21 April, and 9 May. The associated heat units accumulated since 1 January were 617, 877, and 1203 respectively (using 86/55 °F maximum/minimum thresholds respectively). Results indicate that there was a significant interaction between planting date and variety. Overall, lint yields significantly declined with later planting dates and significantly varied among varieties within each planting date.
    • Bollgard® and Bollgard II® Efficacy in Near Isogenic Lines of 'DP50' Upland Cotton in Arizona

      Marchosky, Ruben; Ellsworth, Peter C.; Moser, Hal; Henneberry, T. J.; Silvertooth, Jeff; Department of Entomology, University of Arizona, Maricopa, AZ; USDA-ARS, WCRL, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      The Cry1Ac gene (Bollgard®) is available in cotton either alone ('B') or in combination (Bollgard II®) with a second gene, Cry2Ab ('X'). We evaluated these two different transgenes, separately and together, in near isogenic lines of the upland cotton variety ‘DP50’. DP50B was previously transformed with the Cry2Ab gene to give rise to the experimental line 985BX which was then back-crossed to DP50 to produce near isogenic single gene variants, 985B and 985X. The lepidopteran target was pink bollworm (PBW), Pectinophora gossypiella (Saunders), which was evaluated in two field studies through a series of samples from artificially and naturally-infested bolls. In one study (NTO), three cotton lines (DP50, DP50B, 985BX) were evaluated under three spray regimes. In the second study (Isoline), five near isogenic lines (DP50, DP50B, 985B, 985X, 985BX) were evaluated under two spray regimes: fully sprayed and lepidopteran unsprayed. In lines containing only one transgene, Cry1Ac or Cry2Ab, bolls had consistently fewer PBWs than the non-Bt variety. Very few PBWs developed into large (3rd instar) larvae in these Bt varieties. The majority (NTO: 83%; Isoline: 94%) of PBWs recovered were dead first instar larvae. Less than 5% of the DP50B bolls in the NTO study were infested with feral large (≥3rd instar) larvae, and large larvae were present in less than 2% of naturally-infested bolls of single-gene lines in the Isoline study. PBW age and mortality distributions confirmed that the single transgenes were effective in stopping PBW development and killing young instars. Cry2Ab displayed a broader spectrum of efficacy as it was significantly more effective against citrus peelminer (Marmara spp.), an incidental lepidopteran present in high densities in the tests. The two-gene (Cry1Ac + Cry2Ab) line showed better (at least 10-fold) efficacy than the single-gene lines against PBW large larvae infestation. The PBW age distributions found in this variety consisted almost entirely (98%) of dead first instar larvae. Less than 0.6% of the bolls of the two-gene variety in the NTO study were infested with large (≥3rd instar) larvae, and there was no infestation by large larvae in any of the naturally-infested bolls in the Isoline study. Yields and other agronomic parameters of the two-gene and single-gene varieties were superior or similar to the null parent. Second pick yields of all Bt varieties were significantly higher than the recurrent parent non-Bt line, suggesting a high degree of efficacy against typically high PBW densities during the late season. Cotton lines with transgenes (Cry1Ac & Cry2Ab) separately and combined demonstrated a high degree of efficacy and agronomic performance for usage in Arizona against PBW. The ramifications of isogenic comparisons of PBW incidence on efficacy and resistance monitoring are discussed.
    • Soil and Plant Recovery of Labeled Fertilizer Nitrogen in Irrigated Cotton

      Silvertooth, J. C.; Navarro, J. C.; Norton, E. R.; Galadima, A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Proper timing of fertilizer N applications in relation to crop uptake can serve to improve fertilizer efficiency in irrigated cotton. Earlier research has identified an optimum application window extending from the formation of first pinhead squares to peak bloom, which corresponds well with maximum crop uptake and utilization. Field experiments were conducted at the University of Arizona Marana Agricultural Center (Grabe clay loam soil) utilizing sidedress applications of ammonium sulfate with 5-atom % 15-N at pinhead square, early bloom, and peak bloom at a rate of 56 kg N/ha. The objective was to compare relative efficiencies in terms of fertilizer N uptake and recovery among these three times of application. Results indicate that all treatments averaged approximately 80% total fertilizer N recovery. Of the fertilizer N that was recovered, approximately 40 % was taken up by the plants and 60 % recovered in the soil, primarily in the top 60 cm of the soil profile.
    • Honeydew Production by Sweetpotato Whitefly Adults and Nymphs

      Henneberry, T. J.; Forlow Jech, L.; de la Torre, T.; Silvertooth, Jeff; USDA, ARS, Western Cotton Research Laboratory Phoenix, AZ 85040-8803 (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      We determined honeydew production by male and female sweetpotato whiteflies and the effects of temperature on honeydew production of each sex. We also determined honeydew production by each nymphal instar. Overall, adult SPW produced more honeydew than nymphs. Adult females produced more honeydew than males. The relative differences between honeydew production for males and females and between amounts adults produced compared with nymphs were consistent. However, honeydew production by adult and nymph individuals was subject to large degrees of variation.
    • Agronomic and Economic Evaluation of Ultra Narrow Row Cotton Production in Arizona 1999-2000

      Husman, S. H.; McCloskey, W. B.; Teegerstrom, T.; Clay, P. A.; Wegener, R. J.; Silvertooth, Jeff; University of Arizona Cooperative Extension, Tucson, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Ultra Narrow Row (UNR) and conventional (CNV) cotton production systems were compared with respect to agronomic practices, yield, fiber quality, and production costs in experiments conducted in 1999 and 2000 in central Arizona. Cotton rows were 10 and 40 inches apart in the UNR and CNV systems, respectively. In 1999, the average lint yield in the UNR system, 1334 lb/A, was significantly greater than the 1213 lb/A yield of the CNV system. Similar results were obtained in 2000 with yields of 1472 and 1439 lb/A for the UNR and CNV systems, respectively. Fiber grades of both systems were comparable with most bales receiving a grade of 21 in 1999. The average bale grades in 2000 were 11 and 21 in the UNR and CNV systems, respectively. The quality of the fiber produced in both systems was also comparable with staple and strength measurements meeting base standards in both years. However, there was a consistent difference between the UNR and CNV systems in both years with respect to micronaire. Micronaire averaged 4.5 and 4.0 in the UNR system in 1999 and 2000, respectively, and 5.0 and 4.9 in the CNV system in 1999 and 2000, respectively. Variable growing costs were $607 and $446 for the UNR system in 1999 and 2000, respectively, and $660 and $519 for the CNV system in 1999 and 2000, respectively. Harvest and post-harvest variable costs were $234 and $209 in the UNR system in 1999 and 2000, respectively, and $217 and $224 in the CNV system in 1999 and 2000, respectively. The economic data indicated that the UNR system reduced production costs and increased profitability without sacrificing lint yield or quality. However, these experiments also indicated that many production challenges such as planting and obtaining adequate plant populations, managing plant height control, and weed control need further study.
    • Silverleaf Whitefly Studies: Effects of Trichome Density and Leaf Shape

      Chu, C. C.; Natwick, E. T.; Henneberry, T. J.; Nelson, D. R.; Buckner, J. S.; Freeman, T. P.; Silvertooth, Jeff; USDA, ARS, WCRL, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      We examined nine upland cotton cultivars in 2000 to determine silverleaf whitefly (SLW)-cotton leaf trichome relationships. The hairy leaf cultivar Stoneville 474 had significantly higher numbers of SLW eggs, nymphs and adults compared to eight other smooth leaf cotton cultivars. The top young leaves on main stem terminals had fewer SLW eggs, nymphs and adults, but higher numbers of trichomes compared with older leaves. Among the eight smooth leaf cultivars, the four okra leaf cultivars as a group had fewer SLW eggs, nymphs and adults compared with the four normal leaf cultivars.
    • Relative Susceptibility of Whiteflies to Danital® + Orthone® Over a 5-year Period

      Castle, S. J.; Ellsworth, P. C.; Prabhaker, N.; Toscano, N. C.; Henneberry, T. J.; Silvertooth, Jeff; USDA-ARS Western Cotton Research Laboratory, Phoenix; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; University of California, Riverside, Department of Entomology (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      As part of a program to assess differences in susceptibility to insecticides among regional populations of Bemisia tabaci, insecticide resistance monitoring was carried out at the Maricopa Agricultural Center from fall, 1995 through 1999. Monitoring efforts were concentrated on Danitol®+Orthene® following reports of control problems and documentation of resistance to this mixture in 1995. We were interested in the longer-term dynamics of resistance in light of radically altered treatment regimens beginning with the use of IGRs in 1996. Although the frequency of susceptible individuals to Danitol+Orthene tended to increase in the later years, highly resistant individuals were still present 5 years after the resistance episode of 1995. Whitefly adults collected from various insecticide treatment plots other than Danitol+Orthene were generally uniform in their responses from the time of initial whitefly infestation until defoliation. However, a dramatic shift in susceptibility occurred following a single application of Danitol+Orthene in 1997 and 1999. The increased frequency of resistant individuals following treatment suggests that any large scale return to the use of Danitol+Orthene could rapidly select for proportionally higher numbers of resistant whiteflies and perhaps reduced control in cotton fields.
    • Summary of Nitrogen Management Experiments in Irrigated Cotton

      Silvertooth, J. C.; Norton, E. J.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      A series of nitrogen management experiments have been conducted over the past 11 years around the state to develop and refine fertilizer nitrogen (N) recommendations for irrigated desert cotton production. Stability analysis was used to summarize the data and to determine which of the four treatment regimes is most stable over a range of environments. Results indicate that the feedback treatment (treatment 3) was the most stable treatment for both Upland and Pima cottons and provided the best probability for a higher yield under high yielding environments. The untreated control treatment (treatment 1) was the least stable over a wide range of environments. These results further validate the ‘feedback’ approach to management of fertilizer N.
    • Pest and Pesticide Usage Patterns in Arizona Cotton: Final 2000 Date

      Agnew, G. E.; Baker, P. B.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Arizona's pesticide use reporting (PUR) database is used to track and quantify the general decline in pesticide use in the state. A full summary of the official 2000 growing season pesticide usage is included. The database also enables tracking of changing usage patterns. For two years, target pest information has been included in the Arizona PUR database. Limitations in the PUR database are discussed. The reporting coverage shortfall for insecticide reports in the PUR database is estimated and found to be reasonable relative to sample based approaches to pesticide use reporting.
    • Cotton IPM in Arizona: A Decade of Research, Implemention & Education

      Ellsworth, Peter C.; Jones, Jennifer S.; Silvertooth, Jeff; University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Cotton production in Arizona has been faced with major challenges in insect control during the past decade. These challenges have been met through IPM programs of research, implementation, and education. The decade began (1990) with an outbreak of our key lepidopteran pest, the pink bollworm. Growers sprayed for all pests more than 11 times at a cost of over $113 / A that year. The following years (1991–1995) saw the introduction of and devastation by a serious, quality-reducing insect, the sweetpotato or silverleaf whitefly. Growers sprayed up to 6.6 times (1995) at a cost of over $145 / A to combat this single insect pest. The cotton IPM program at the University of Arizona along with industry, grower, and USDA partners readied farmers for the introduction (1996) of two strategic sets of pest control technology, ‘Bt’ transgenic cotton and insect growth regulators (IGR). Through an aggressive educational campaign, growers learned about the safe, effective, and sustainable use of these technologies. As a result, cotton growers saw their average spray requirement plummet from 12.5 sprays at $217 / A (1995) to an historic low of 1.91 sprays at $37 / A (1999). Now new threats from an old pest, Lygus bugs, pose serious challenges to these staggering advances in cotton IPM. This paper highlights the key advances made in research, implementation, and education during this volatile decade. Furthermore, we conclude with one example how systematic, large-scale, and long-term research can provide insight into the role that new technology and the knowledge to use it properly have on cotton grower and industry success.
    • Nitrogen Management Experiments For Upland and Pima Cotton, 2000

      Silvertooth, J. C.; Norton, E. R.; Galadima, A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Two field experiments were conducted in Arizona in 2000 at two locations (Maricopa and Marana). The Maricopa experiment has been conducted for nine consecutive seasons; the Marana site was initiated in 1994. The purposes of the experiments were to validate and refine nitrogen (N) fertilization recommendations for Upland cotton. The experiments 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 benefit yields at any location. In 2000, fruit retention levels were good and crop vigor was not excessive. The more conservative, feedback approach to N management provided optimum yields at both locations.
    • Evaluation of a Calcium-Based Soil Conditioner in Irrigated Cotton

      Silvertooth, J. C.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      A two site evaluation of a calcium (Ca²⁺)-based soil conditioner was conducted during the 1999 cotton season. The two locations included one at the Maricopa Agricultural Center (MAC) in Maricopa, AZ and the other was on a grower-cooperator field in Tacna, AZ. Both studies involved the use of CN-9, a Ca-nitrate solution with 9% nitrogen and 11% Ca. At MAC theCN-9 solution was sprayed over the seedbed post planting but prior to the first water-up irrigation. At the Tacna site CN-9 was applied in a sidedress application at planting. Routine plant measurements were taken throughout the duration of both studies and lint yield estimates were made at each location at the end of the season. No significant differences due to the application of CN-9 were detected in any data collected.
    • Evaluation of Crop Management Effects on Fiber Micronaire, 2000

      Silvertooth, J. C.; Galadima, A.; Norton, E. R.; Tronstad, R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Arizona has experienced a trend toward increasing fiber micronaire values in recent years resulting in substantial discounts on fiber value. There is some evidence to suggest management can impact fiber micronaire. Approximately 250 cases were identified in cotton production areas in Arizona ranging from the lower Colorado River Valley to near 2,000 ft. elevation with grower cooperators in the 2000 season. Field records were developed for each field by use of the University of Arizona Cotton Monitoring System (UA-CMS) for points such as variety, planting date, fertility management, irrigation schedules, irrigation termination, defoliation, etc. Routine plant measurements were conducted to monitor crop growth and development and to identify fruiting patterns and retention through the season. As the crop has approached cutout and the lower bolls began to open, open boll samples have been collected from the lowest four, first position bolls (theoretically the bolls with the highest micronaire potential on the plant) from 10 plants, ginned, and the fiber analyzed for micronaire (low 4). From that point forward, total boll counts per unit area and percent open boll measurements are being made on 14-day intervals until the crop is defoliated. Following defoliation, final plant maps were performed. Relationships among low 4 samples micronaire, irrigation termination (IT), defoliation, and final crop micronaire were analyzed.
    • Evaluation of Potassium and Phosphorus Fertility in Arizona Soils

      Silvertooth, J. C.; Norton, E. R.; Galadima, A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 2001)
      Two field experiments were conducted during the 2000 growing season to address fertility recommendations for fertilizer phosphorus (P) and potassium (K). A K fertility study was conducted near Tonopah, AZ consisting of two treatments, an untreated control and a treatment receiving a total of 20 gallons of K-Sul/acre. No significant differences were observed in leaf blade K concentrations between treatments. Plant growth and development estimates revealed that fruit retention (FR) levels remained consistently higher in the untreated control versus the treated plots. A second study involved treatments consisting of both P and K fertilizers was conducted near Cibola, AZ. Four treatments in this experiment included an untreated control plus treatments of 11-52-0, 0-0-60, and 4-17-40 at 100, 200, and 300 lbs. fertilizer/acre respectively. Plant growth and development estimates were similar among treatments during the season. At the end of the season the untreated control had a slightly higher FR level than the other treatments, which also produced a significantly higher yield. No other differences in yield among the fertilized treatments were observed.