• Pink Bollworm and Cabbage Looper Motalities and NuCOTN 33B (Bt) Cry1Ac Contents in Cotton Fruiting Forms and Leaves on Increasing Numbers of Days after Planning

      Henneberry, T. J.; Forlow Jech, L.; de la Torre, T.; Maurer, J.; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Studies were conducted to follow seasonal susceptibility of feral pink bollworm (PBW), Pectinophora gossypiella (Saunders) larvae to NuCOTN 33B (Bt) and Deltapine (DPL) 5414 in furrow and furrow plus supplementary drip-irrigated cotton field plots. Laboratory bioassays of laboratory - reared PBW larvae to flower buds and bolls and cabbage looper (CL), Trichoplusia ni (Hübner), larval mortality feeding on DPL 5415 and Bt cottons leaves were also conducted. Cry1Ac insect toxic protein contents in the different plant tissue were determined by Enzyme Linked ImmunoSorbent Assay (ELISA) throughout the season to compare in relation to PBW and CL mortality data. Irrigation type had no effect on PBW or CL larval mortality parameters measured. DPL 5415 bolls had 0.15 feral live larvae per boll and no dead larvae per boll compared with no live and 0.12 dead feral larvae per Bt boll. Whole plant samples showed 0.5 to 8.6% live larvae boll infestations compared to no live PBW life stages and no exit holes for Bt bolls. No PBW larvae survived on day four following bioassay infestation of one-third grown Bt flower buds with PBW neonate larvae as compared to 90% larval survival on DPL 5415 flower buds. Immature bolls harvested in the field and artificially infested with PBW larvae in the laboratory showed averages of 3 to 52% live larvae per boll, all in fourth instar of development, for DPL 5415 bolls compared to no live larvae, no development beyond the first instar, and no exit holes for Bt bolls. Cry1Ac protein level in flower buds were 0.11 to 0.16 ppm and 0.14, 0.11 and 0.05 ppm, in each case, per wet weight gram of boll tissue in bolls during the season. For CL leaf bioassays, larval mortalities after 7 days feeding on Bt leaves were variable ranging from 82 to 94% from node 8 on 61 and 82 days after planting (DAP) to 32, 38 and 7% on leaves from node 16 on 82, 117, and 159 DAP, respectively, and 28 and 6% on leaves from node 24 on 117 and 159 DAP. Cry1Ac amounts were 0.96 and 0.85 ppm (wet wgt per g of Bt leaf tissue), from leaves from node 8 (61 and 82 DAP), 0.53, 0.50 and 0.22 ppm (node 16, 82, 117, and 159 DAP) and 0.44 and 0.18 ppm (node 24, 117 and 159 DAP). Numbers of cotton bolls, lint and seed per acre were significantly greater from plots that were furrow plus drip irrigated as compared to furrow irrigated alone. DPL 5415 and Bt cotton yields were not significantly different.
    • Susceptibility of Arizona Pink Bollworm to Cry1Ac

      Sims, Maria A.; Dennehy, Timothy J.; Shriver, Laura; Holley, Danny; Carrière, Yves; Tabashnik, Bruce; Antilla, Larry; Whitlow, Mike; Department of Entomology, University of Arizona, Tucson, AZ; Arizona Cotton Research and Protection Council, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Genetically modified cotton expressing the Cry1Ac toxin 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. Since 1995, average insecticide use in Arizona cotton has declined from greater than six applications per acre to less than two in 2000. Bt cotton has contributed greatly to these savings to growers, as have insect growth regulators used for whitefly control. Collections of pink bollworm, Pectinophora gossypiella, made in 1997 and subsequently exposed to Cry1Ac in the laboratory from 1998 to 2000, yielded a laboratory strain with susceptibility to Cry1Ac reduced 1,000 to 3,000- fold, relative to highly susceptible field populations. Unparalleled measures have been taken to detect and manage this resistance. In this report we summarize results of statewide monitoring of pink bollworm susceptibility to Cry1Ac conducted from 1997 to 2000, and results of field evaluations of the effectiveness of Bt cotton from 1995 to 2001. Susceptibility of Arizona pink bollworm to Cry1Ac, increased from 1997 to 2000. Mean corrected mortality in 1μg/ml Cry1Ac assays was 57.4% in 1997, 90.6% in 1998, 97.9% in 1999 and 97.4% in 2000. Mean corrected mortality in bioassays of 10 μg/ml also increased: it was 94.1% in 1997, 99.9% in 1998, 100% in 1999 and 100 % in 2000. Field performance of Bt cotton in 2000 continued to be excellent at 39 locations throughout Arizona cotton at which paired Bt and non-Bt fields were evaluated. Whereas non-Bt cotton fields had mean infestations of over 15% infested bolls, Bt cotton fields averaged less than 0.15% infested bolls. Thus, after six years of intensive use of Bt cotton in Arizona, pink bollworm populations show no signs of being resistant to Bollgard cotton. Indeed, for reasons that are not understood at this time, they have been found to be significantly more susceptible to the Bt toxin in Bollgard cotton at the end of the 2000 season than they were in 1997.
    • Pink Bollworm: Diapause Larval Exit from Harvested Immature Cotton Bolls and Percentages Surviving to Moth Emergence

      Henneberry, T. J.; Forlow Jech, L.; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Pink bollworm (PBW), Pectinophora gossypiella (Saunders), diapause larval exit from immature green bolls and larval and pupal mortality after exiting bolls, were studied at Phoenix, AZ in the insectary. Diapause larvae exited immature bolls sporadically during January, February, and early March. Thereafter, exit from the bolls was more consistent and highest numbers emerged in late April, May or early June. Larval and pupal mortality were high during January to early February and March, decreased in mid-March through early June, and increased again in mid-June to early August. Larvae remained in immature bolls as long as 319 days after harvest. Moth emergence was significantly correlated to accumulated heat units (12.8 and 30.6°C lower and upper developmental thresholds).
    • Defoliation of Pima and Upland Cotton at the Safford Agricultural Center, 2001

      Clark, L. J.; Coleman, R. D.; Carpenter, E. W.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      Nine defoliation treatments based on standard and reduced rates of Ginstar and Chlorate plus two additives (compounds F and S) were applied to Pima and Upland cotton to compare the treatment effects on percent leaf drop and yields. All of the treatments were beneficial to leaf drop compared to the untreated check with the Ginstar treatments generally performing better than the Chlorate. Both of the additives enhanced the early defoliation effectiveness for the reduced rates of Chlorate and Ginstar over all other treatments, including the full rates of the Chlorate and Ginstar. Generally, this same enhanced effectiveness was seen of the additives plus reduced rates over the full rates of Chlorate and Ginstar throughout the defoliation process. This is the second year of the study.
    • Evaluation of Irrigation Termination Effects on Fiber Micronaire and Yield of Upland Cotton, 2001-2002

      Silvertooth, J. C.; Galadima, J. (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      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 that irrigation termination management can impact fiber micronaire. Field studies were conducted in 2000 and 2001 at the University of Arizona Maricopa Agricultural Center (MAC; 1,175 ft. elevation) and the Yuma Valley Agricultural Center (YVAC; 150 ft. elevation) to evaluate the effects of three dates of irrigation termination on the yield of several Upland cotton varieties. Three dates of irrigation termination (IT1, IT2, and IT3) were imposed based upon crop development. The earliest irrigation termination date, IT1 was made slightly ahead of an optimum date 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. Thus, the IT1 date was imposed to try to reduce overall micronaire. The second termination (IT2) date provided one additional irrigation over an optimal point for the first cycle fruit set and two irrigations beyond IT1. The final (IT3) date (later September) was staged so that soil moisture would be sufficient for the development of a full top-crop potential. Lint yield and micronaire results have consistently revealed significant differences among the IT treatments. The micronaire values were consistently less than 5.0 for the IT1 treatments. Micronaire and lint yield values increased with later IT dates.
    • Upland Cotton Variety Evaluation in Graham County

      Norton, E. R.; Clark, L. J. (College of Agriculture, University of Arizona (Tucson, AZ), 2002-06)
      A field trial was established during the 2001 growing season as part of the statewide Upland Cotton Variety Testing Program. This trial was located in Thatcher with Dennis Layton Farms as the cooperator. The location was one of eleven around the state. Seven Upland cotton varieties to be evaluated at this location were entered by various cooperating seed companies. A new variety from FiberMax produced the highest yield and also possessed the highest quality fiber making it the variety that would have produced the highest gross income to the producer.
    • Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2001

      Silvertooth, J. C.; Galadima, A.; Norton, E. R. (College of Agriculture, University of Arizona (Tucson, AZ), 2002-03-18)
      Field experiments were conducted in Arizona in 2001 at three locations (Maricopa, Marana, and Safford). The Maricopa and Safford experiments have been conducted for14 consecutive seasons 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 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 Maricopa, Marana, and Safford, respectively.