Six short staple cotton varieties including two New Mexico acalas varieties and one advanced strain, an Australian varieties and two SureGrow varieties with higher yield potential were tested in this study. New Mexico Acala 1517-95 had the highest lint yield with a yield of 419 pounds of lint per acre. The average yield was about 400 pounds per acre lower than the 6 year average due to a cold spring and a four inch rain that fell in one hour in the middle of July. In addition to lint yields; percent lint, plant heights, plant populations and lint hvi values are shown. A lint yield comparison for 1993 through 1998 is included in this paper.

Green bolls (100/field) were sampled from the uppermost internodes within adjacent fields of Bt (Deltapine 33B) and non-Bt refuge (Hyperformer HS 44 or Deltapine 20) experiencing severe pink bollworm pressure late in the growing season. Evidence of 3rd instar or larger pink bollworm larvae survival was higher in susceptible bolls sampled from transgenic Bt cotton late in the 1998 growing season, compared to that observed late in the 1997 growing season.

Several field experiments were conducted in many of the cotton growing areas of Arizona in 1998 for the purpose of evaluating agronomic characteristics of many new transgenic Upland cotton varieties. In many cases, the new transgenic lines were compared directly with their recurrent (nontransgenic) parents. Evaluations were carried out by collecting plant mapping data from each variety on a regular 14 day interval throughout the season and relating the resultant information to established baselines for Upland cotton in Arizona. Lint yield measurements were also taken on each variety at all locations. Results indicate that all transgenic lines tested are very similar to their recurrent parents in terms of growth, development, and yield. Some subtle differences were noted but they were very slight and should not impact management of the varieties significantly in comparison to their recurrent parents.

As more transgenic varieties become available, grower=s interests intensify and more information is needed to satisfy the inquiries. Agronomic comparisons of six lines (transgenic varieties and their recurrent parents) from three companies are represented in this high desert study. Results show some subtle differences between the transgenic lines and their recurrent parents. Under the high Pink Bollworm pressure observed in the trial, yield increases were uniformly seen when the Bt gene was present, even though all plots were sprayed to control insect pests. Yields tended to be lower when herbicide resistence was introduced into the plants (even though not statistically significant), except when placed in a stacked array. Several agronomic values and HVI lint quality values are reported in this report.

Variety trials were grown at two locations and with two different sets of short staple varieties. One trial on the Robbs farm, north of Kansas Settlement, tested two acala varieties and the most promising advanced strain from New Mexico, two short seasoned varieties from SureGrow and one Australia variety. The other trial on the Glenn Schmidt farm, in Kansas Settlement, tested seventeen upland varieties as part of the statewide testing program. The highest yielding variety in the Robbs trial was SG 404 with SG 125 coming in second. In the Schmidt trial, FM 989, an Australian variety that has performed well in Safford, had the highest yield, just over 2 bales per acre.

Lygus became the number one pest of cotton in 1998 with statewide losses of over $16 million in spite of individual costs to the grower of over $55/A for control. Selective technologies for whitefly and pink bollworm control reduce the number of broad spectrum sprays that incidentally control Lygus. Control of Lygus depends mainly on just two related chemical classes of insecticides, organophosphates and carbamates. Over reliance on such a limited diversity of chemical controls increases the risk of resistance. Further, FQPA threatens the future availability of many of our main stay chemical controls. The study reported here sought to investigate the commercial suitability of a new compound, Regent®, for the control of Lygus. This novel mode of action represents one of the few potential new tools under development for Lygus management. Under a federal Emergency Use Permit (EUP), Regent was tested against two standards of Lygus control (Orthene® and Vydate®) and an untreated check. In a test of unusually high Lygus densities, Regent provided excellent control of small (instars 1–3) and large (instars 4–5) Lygus nymphs and may provide marginally better control of adults than current standards. None of the tested agents provided quick control or knockdown of adults. Rather, adult levels were reduced over time, most likely as a result of prevention of the development of new adults via nymphal control. All three materials protected cotton producing yields significantly higher than the check. The Orthene treatment had the highest yield, though not significantly higher than the Regent treatment which was effectively sprayed one less time than the other compounds.

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.

Starting in 1993, we developed a field-based protocol for bioassaying sweetpotato whiteflies (SWF) for susceptibility to buprofezin (Applaud®). Since then, we have monitored Arizona SWF populations (up to 5 regions) for susceptibility to Applaud in four out of the last six seasons. We observed no appreciable decrease in susceptibility. Instead, we have observed an increase in susceptibility of present day whiteflies when compared to populations bioassayed in 1993 and 1996, before any Applaud use in the U.S.. This result, however, is likely related to various procedural changes in the bioassay methodology. Nevertheless, our current estimates of whitefly susceptibility are similar to those obtained from various unexposed populations from around the world and to populations we bioassayed in 1997. Differences between our LC50 estimates and those of some other researchers can probably be explained by various procedural differences: 1) method of Applaud application, 2) whitefly stage collected and sources of leaf foliage, and 3) bioassay environmental conditions. Our results also showed each year that Applaud susceptibility does not decline after Applaud application(s) based on commercial paired field comparisons and replicated small and large plot evaluations. In fact, susceptibilities actually marginally increased after an Applaud application. This fact does not alter the recommendation for Arizona to limit Applaud use to one time per crop season, but does provide hope for the development of a sustainable use pattern even if usage continues on non-cotton hosts (i.e., on melons and vegetables under Section 18). Given the tremendous value of this mode of action, however, commodity groups should work together wherever possible to coordinate the usage of this and other valuable compounds so that whitefly generations are not successively exposed to this product.

Direct-observation studies were conducted in replicated experimental plots to identify causes and estimate rates of mortality of whiteflies in cotton over the course of six generations from late June through late October. In plots receiving no whitefly or Lygus insecticides, predation and dislodgment were major sources of egg and nymphal mortality, and overall survival from egg to adult ranged from 0-18.2%. Similar patterns were observed in plots treated with the insect growth regulator (IGR) Knack. Applications of the IGR Applaud or a mixture of endosulfan and Ovasyn caused high levels of small nymph mortality and reduced rates of predation on nymphs during the generation immediately following single applications of these materials in early August. Whitefly populations declined to very low levels by mid-August in all plots, and few differences were observed in patterns of whitefly mortality among treated and control plots 4-6 weeks after application. The population crash was associated with an unknown nymphal mortality factor which reduced immature survivorship during this first posttreatment generation to zero. The application of insecticides for control of Lygus in subplots modified patterns of mortality in all whitefly treatments by generally reducing mortality from predation during generations observed from mid-July through August. Parasitism was a very minor source of mortality throughout and was unaffected by whitefly or Lygus insecticides.

Trehalulose and melezitose produced by Bemisia argentifolii Bellows and Perring and thermodetector counts in cotton lint increased with increasing numbers of days of exposure of open cotton bolls in infested cotton plots. Thermodetector counts were significantly correlated to amounts of trehalulose and melezitose. Rainfall of 0.5 inch reduced trehalulose and melezitose in cotton lint within 5 h following the rain. The results suggest dissolution of the sugars followed by runoff as opposed to microbial degradation.