• Upland Cotton Lint Yield Response to Several Soil Moisture Depletion Levels

      Husman, Stephen H.; Johnson, K.; Wegener, R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Upland cotton lint yield response to several soil moisture depletion levels was measured in 1997 and 1998. In 1997, four Upland cotton varieties including DP 5415, DP 33B, DP 5816, and STV 474 were tested. However because of a nonsignificant variety difference in the 1997 test, the 1998 test was planted to a single variety (DP 33B). In 1997 and 1998, depletion of plant available soil water (PAW) irrigation treatments consisted of 35%, 50%, 65%, and 80%. In 1997, all PAW depletion treatments were significantly different with the 35% PAW treatment resulting in the highest average lint yield of 1880 lbs. lint/acre. The 50%, 65%, and 80% PAW treatments resulted in 1410, 1123, and 248 lbs. lint/acre respectively. There was no significant (P<0.05) difference between varieties within all PAW treatments in 1997. In 1998, all PAW depletion treatments again were significantly different with the 35% PAW treatment resulting in the highest average lint yield of 1658 lbs. lint/acre. The 50%, 65%, and 80% PAW treatments resulted in 1534, 1396, and 641 lbs. lint/acre respectively.
    • Upland Regional Cotton Variety Test at the Maricopa Agricultural Center, 1998

      Hart, G. L.; Nelson, J. M.; Clark, Lee J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Thirty six 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 populations, plant heights and fiber properties are presented in this paper.
    • Whitefly Management with Insect Growth Regulators and the influence of Lygus Controls

      Ellsworth, Peter C.; Naranjo, Steve E.; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      The three keys to whitefly management are sampling, effective chemical use, and avoidance. This study examines factors relevant to the latter two keys in the context of Arizona’s cotton pest spectrum. Insect growth regulators (IGRs) are central to Arizona’s success in whitefly management. The basic usage guidelines developed for the IGRs—initial treatment timing, prescribed intervals between successive uses, and one use each seasonal limits—are all valuable in the development of a sustainable use pattern. Re-treatment timing guidelines for the second IGR has been the subject of investigation for the past two years. However, whitefly pressure in 1998 was strikingly different and lower than in any other post-introduction year. Re-treatment was unnecessary and thus could not be evaluated this year. Lygus, on the other hand, were at damaging levels early in plant development and for a protracted period. Future successes in whitefly management should consider the whole pest spectrum and depend on integrating chemical controls for all sprayed pests. While our primary focus is to optimize management of whiteflies in the context of other pests, this study examined the impact of Lygus controls on whitefly population dynamics and cotton production. Three sprays were required to control Lygus populations in this study. These sprays were atypically non-disruptive to whitefly population dynamics, and instead, helped to suppress low-level populations of whiteflies even further. This lack of disruption may have been due in part to the reduced abundance and role of natural enemies in this study. Lygus sprays did protect yields with a 3-fold advantage over untreated plots. Furthermore, there were a series of negative consequences of poor Lygus control. Plants tended to be more vegetative and more difficult to defoliate. Lower lint turnouts were documented for the Lygus-untreated areas. Sources of this additional loss were identified and included increased gin trash and larger seed size in Lygus-untreated areas. The lint also had significantly more sticking points as measured by manual thermodetector. While all cotton was determined to be non-sticky, this increased contamination may have been also related to the higher trash levels. Because of the differences in outcome in 1997 and 1998 in terms of Lygus spray effects on whiteflies, it is even more imperative that we further test whitefly management systems under near commercial conditions. A better understanding of the relationship between the control programs for these two major pests will help guide decisions on remedial inputs. This study also serves as an annual, replicated, and systematic accounting of whitefly population dynamics and control requirements useful for making historical comparisons across years. Inferences may be drawn about what are and are not the underlying causes of the unusual population dynamics observed in 1998.