This study evaluated the effectiveness of defoliating at various heat unit accumulations: 630HU, 730 HU, 830 HU, 930 HU, 1030 HU, 1130 HU and 1330 HU and impact on lint yield and fiber quality. American Upland cotton variety DP 449 BR was planted on 12 April 2005 at the University of Arizona Maricopa Agriculture Center in Maricopa, Arizona. The experimental design was a split plot with four replications of each of seven defoliation timings. Final irrigation occurred on 05 August 2005. When heat unit accumulation reached 630 HU (on 20 August 2005), 730 HU (on 01 September 2005), 830 HU (on 04 September 2005), 930 HU (on 08 September 2005), 1030 HU (on 12 September 2005), 1130 HU (on 19 September 2005) and 1330 HU (on 27 September 2005) using the 86/55 F model chemical defoliants were applied. A mixture of Def (tribufos) at 24 oz/A, Dropp (thidiazuron) at 0.2 lb/A and Prep (ethephon) at 24 oz/A was applied using a high clearance research sprayer. The earliest treatments (630 and 730 HU accumulated) had significantly fewer open bolls at defoliation than those that received later treatments. At harvest, this trend disappears: the latest application (at 1330 HU) had significantly fewer open bolls than any other timing. Seven days after defoliant application (7 DAT), highest levels of defoliation were observed in the following treatments in descending order: 830 HU, 630 HU, 1130 HU, 930 HU and 730 HU followed by 1030 HU and 1330 HU. At harvest, there were no significant differences among mean defoliation percentages with the exception of the 1330 HU timing, which was significantly less defoliated than any of the other timings. Highest lint yield and gin turnout were observed in the earliest defoliation timings, lowest in the later timings. No significant differences in micronaire, length or uniformity were observed between defoliation timings. Differences did occur in fiber strength which was highest in earlier timings and lowest in the last timing, but all were above the discount level.

A rapid heat increase from the high 80s-low 90s to high temperatures of 110o F on May 21 and 22, 2005, was recorded in the Blythe, CA, area, resulting in abnormal cotton flowers in mid-June, being especially characterized by elongated styles and stigmas being beyond the anthers. Two different cotton variety trials conducted in the Palo Verde Valley allowed data to be collected semi-weekly beginning June 17-20, with 100+ flowers per plot examined in each plot (four replications) of each of the 14 cotton variety entries. Every cotton variety had an average of 90+% of flowers expressing heat stress abnormalities (elongated styles) at the beginning of data collection even though the trials varied by planting date and location. Abnormal flowers were noted for several weeks, with some stigmas 21 mm beyond the anthers. Varieties differed in their responses to heat stress as measured by elongation later in the summer. Limited data were also collected for fruit retention and correlated with length of stigma extension beyond anthers. Retention percentages decreased as distance between anthers/stigmas increased, however boll size increased with less retention, possibly through nutrient partitioning. Various foliar fertilizers containing calcium were also evaluated for their effect on stigma elongations of DPL 449BR cotton. Significant differences existed for stigma elongations, with 2.5 qts./acre of CalMax resulting in statistical reduction of elongation when compared with the untreated check at 3 weeks after application. Statistical differences did not exist at four weeks although statistical differences did exist at this date for the percentage of flowers affected, with the highest percentage (81.7%) noted in untreated cotton.

Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2001-2005, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 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 (G. 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 consistently 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 N fertilizer was applied. Therefore, all N taken-up by the crop was assumed to be derived from residual soil N. However irrigation water analysis showed that NO₃⁻-N concentration levels added to the crop ranged from about 5-9 ppm. In 2001-2005 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 season. Trends associated with residual fertilizer N effects are not evident at either location for five seasons following N fertilizer applications.

A series of experiments were conducted across two locations in Arizona to evaluate 32 advanced and preliminary strains from the Arizona Cotton Growers Breeding Program. These trials were conducted in Yuma, AZ (130 ft. above MSL) and Maricopa, AZ (1170 ft. above MSL). Strains were planted in four row plots extending 38 feet in a randomized complete block design with a minimum of four replications. Each location had three commercial cotton varieties included as control treatments for comparison. Data collected on these trials included a series of plant measurements at three growth stages over the course of the season and yield and fiber quality data. All data were subjected to statistical analysis to test for differences among strains for yield and fiber quality. Both locations produced high yields despite high levels of heat stress in the lower deserts. Statistically significant differences were observed in yield and all fiber quality parameters at each location. Yield was down in Yuma as compared to previous years ranging from 1100 to 1800 lbs lint/acre. Yield at Maricopa was up significantly from last year with yields ranging from 1400 to 2100 lbs lint/acre. Significant increases in staple length was observed with several ACGA lines over control varieties at both locations with one line in particular producing a staple length of nearly 40 (ACGA 107). Several ACGA lines possess excellent fiber quality and performed well in terms of yield at both locations.

The upland cotton variety trial has been conducted in Arizona every year for the past 6 years to evaluate several varieties of upland cotton. Varieties planted at each location are planted side-by-side to evaluate performance and yield under the same growing conditions. Eleven locations were planted in Arizona in 2005. These locations include two locations in the Yuma Region (Yuma County), two locations in the Western Region (La Paz and Mohave Counties), four locations in the Central Region (Maricopa and Pinal Counties), one location in the Southern Region (Pima County), and two locations in the Eastern Region (Graham and Cochise Counties). Each site had between seven and eleven varieties evaluated for yield and quality of lint.

Two separate Upland cotton variety evaluations were conducted in southeastern Arizona during the 2006 cotton growing season. One location was in Graham County (Thatcher), while the second location was in Cochise County (Kansas Settlement). Sixteen varieties were planted at the Thatcher and ten varieties were selected and planted at the Kansas Settlement location. Varieties ranged in maturity from early to full at each of the locations. All plots were arranged in a randomized complete block design with four replications. Both locations were planted on grower-cooperator fields and were managed in accordance to the individual grower styles. Plant measurements were collected over the course of the season at only the Thatcher location. Lint yield was determined by harvesting the entire plot at each location and weighing the resultant seedcotton. Sub-samples were collected also at the time of harvest for percent lint estimates and fiber quality analysis. Crop value was calculated multiplying the lint yield by a lint price determined by a base value of $0.52/lb plus any discounts or premiums based upon fiber quality. Lint yield levels at both locations were high ranging from 1200 to just over 1900 lbs. lint/acre with a new Acala variety from Phytogen (PHY745WRF) producing the highest yield and also the highest crop value at the Thatcher location. In Kansas Settlement lint yields ranged from 1000 to over 1500 lbs. lint/acre with the highest lint yield and total crop value being produced again by the new Acala variety from Phytogen (PHY745WRF).

When a product performs better or worse than expectations, there are many biological, ecological, and operational factors that must be examined. Genetic resistance to the pesticide itself is often a concern. The control interval depends on the ecological impact of biotic (e.g., presence and function of natural enemies) and abiotic (e.g., frequency and severity of storms) factors. Timing, rates, and application methods used are also key factors affecting product performance. A four-year study to evaluate pyriproxyfen (Knack®) field performance in Arizona was initiated in 2004, after levels of whitefly susceptibility in statewide surveys were observed to be decreasing. Grower sites in Maricopa, Buckeye, Wellton, and Marana were used. We controlled for major operational factors by using a common timing, rate, and aerial application for each Knack spray. Resistance bio-assays were conducted on progeny of field-collected adults, pre- and post-spray. New eggs were marked in-field prior to spraying and examined in the field and lab in order to isolate Knack-associated mortality caused by direct toxicity as well as by ecological factors (e.g., bioresidual). Nymphal bioassays were used to evaluate metamorphosis inhibition. Population trends were estimated using standard sampling methods. Appropriate check plots were compared to the Knack treatment. Study results suggest Knack field performance and pyriproxyfen resistance has not changed significantly among the years or locations examined to date. In 2005, many struggled to gain control over whitefly populations. This work indicated that Knack performance and resistance parameters were within the range expected for the last several years. However, operational and ecological barriers to the performance of Knack and other chemistry were in play. Late planted conditions, lush winter vegetation capable of hosting whiteflies, poor growing conditions, and an extended period of extreme immigration pressure were all factors that diminished the impact of Knack and other products in 2005. In contrast, the winter preceding 2006 was among the driest on record followed by a very active monsoon season in central Arizona. High winds and dust movement, and a very active natural enemy community helped to continually lower whitefly populations. The result was a whitefly season characterized as light, with overall foliar insecticide usage setting a 28-yr record low for Arizona cotton. Barring all other operational and ecological factors at work, control intervals should have been similar each year. Yet, observed intervals have been different (e.g., 2005 vs. 2006) and point to the importance of these external factors in assessing product performance. Work will continue in 2007 to identify factors that contribute to whitefly outbreak conditions. These data will be key to understanding any performance changes, either due to operational or ecological factors mentioned above or due to innate changes in whitefly susceptibility. This will be important in advising growers about the risk factors associated with whitefly outbreaks and should lead to recommendations for minimizing these risks.

A series of experiments were conducted across three locations in Arizona to evaluate over 50 commercial cotton strains. These trials were conducted in Yuma, AZ (130 ft. above MSL); Maricopa, AZ (1170 ft. above MSL); and Safford, AZ (2900 ft. above MSL). Strains were planted in four row plots extending 38 feet in a randomized complete block design with a minimum of three replications. Each location had three commercial cotton varieties included as control treatments for comparison. Data collected on these trials included a series of plant measurements at three growth stages over the course of the season, plus yield and fiber quality data. All data was subjected to statistical analysis to test for differences among strains for yield and fiber quality. Trials conducted at both Yuma and Safford performed extremely well with yields ranging from 1200 to over 2400 lbs. lint/acre. The Maricopa test site experienced some adverse weather (high levels of heat stress) and insect related conditions that led to overall decreased yields. Ranges in yield were from approximately 400 to just over 1600 lbs. lint/acre. Significant differences among lint yield and fiber properties were experienced at every location. Plant measurement results also demonstrated interesting trends among strains and locations.

A defoliation experiment was conducted during the 2005 growing season in an effort to evaluate effectiveness of the Ginstar™ defoliant alone and in combination with Cotton Quick™. This study was conducted at the University of Arizona Safford Agricultural Center on Upland (cultivar DP655BR). Plots were planted on 22 April. Treatments were arranged in a randomized complete block design with four replications and treatments that included Ginstar™ at 6 and 8 oz./acre rates and Ginstar™ at the 6 and 8 oz./acre rates in combination with various rates of Cotton Quick™ (1.5, 2, 3, and 4 pts/acre). A control, not receiving any harvest prep material was also included for a total of eleven treatments. Treatments were imposed on 3 October and evaluations were made on 14 October and 26 October. Estimations on percent leaf drop, regrowth control, and open boll were made. Lint yield was estimated by harvesting the center two rows of each plot and sub-samples were collected for fiber quality analysis. Plots were harvested on 26 October in an attempt to evaluate the boll opening effectiveness of the Cotton Quick™ material. Results indicated increased leaf drop in lower Ginstar™ rates with the addition of Cotton Quick™. Measurements of open boll percentages did not indicate any increase with the addition of Cotton Quick™ however, lint yield and fiber quality parameters would demonstrate otherwise. Lint yield slightly increased in all treatments receiving Cotton Quick™ while fiber micronaire decreased in Cotton Quick™ treatments. This would indicate a blending of less mature bolls opened with the addition of Cotton Quick™ with those already opened. Percent lint also increased in all treatments receiving Cotton Quick™.

A single experiment was conducted in 2005 at the University of Arizona Safford Agricultural Center in an effort to continue to evaluate several different formulations of the plant growth regulator (PGR) mepiquat chloride. Plots were established with the cultivar Deltapine DP 655BR on 19 April 2005. Four treatments were imposed on 18 July 2005 of 16 oz./acre applications of Mepex, Pix Ultra, and Pentia, plus a control plot. Plots were four 36” rows wide and extended the length of the irrigation run of 220 feet. Plots were arranged in a randomized complete block design with four replications. Plots were monitored with respect to plant growth and development through collecting plant measurement data over the course of the season. Yield results were obtained by harvesting the center two rows of each plot and weighing the resultant seedcotton. Fiber quality was determined from a sub-sample collected from each plot at harvest. Plant growth and development trends indicated strong fruit retention levels all season with strong early season vigor. Each of the PGR applications had significant impact on plant height effectively reducing internode elongation. Lint yield results indicated increased yields for all PGR applications over the control with Pentia producing a statistically significant higher yield. Fiber quality was also impacted by PGR application. All PGR treatments had trends toward higher staple length, fiber strength, and fiber uniformity. These results are consistent with previous results indicating that PGR applications have the potential to increase yields under situations were high vigor is present.