Defoliation tests were conducted on Upland and Pima cotton at the Maricopa Agricultural Center to evaluate rates of Ginstar, tank mixes of Ginstar with other defoliants and spray adjvants, and Ginstar used as a preconditioner. The cotton used in these tests was generally difficult to defoliate, probably because of an excessive supply of nitrogen and cool temperatures in October and November. In September tests, no treatment gave acceptable defoliation of Upland cotton and only the highest rate of Ginstar and the Ginstar + Def treatment were effective on Pima cotton. In October and November tests, temperatures were cool and Upland cotton was not consistently defoliated by a single application of defoliant. Pima cotton was effectively defoliated by Ginstar treatments in early October and November tests. Under cool weather conditions when defoliation was very difficult, Ginstar used as a preconditioner at .047 lb. a. i./acre followed by Ginstar at .094 lb. a. i./acre generally gave acceptable defoliation.

Two field experiments were conducted near Coolidge and Marana, AZ in 1996 to evaluate the effectiveness of a number of defoliation treatments on Upland (var. DPL 5415) and Pima (var. S-7) cotton.. All treatments consisted of materials commercially available in Arizona, and each showed promise in terms of overall effectiveness. Results do reinforce recommendations regarding the use of low rates (relative to the label ranges) under warm weather conditions and increasing rates as temperatures cool.

Nine defoliation treatments were applied to Pima and upland cotton to compare the treatment effects on percent defoliation of the plants, percent first pick values, percent gin trash and any effects they might have on fiber qualities. All of the treatments were beneficial compared to the untreated check, but differences between treatments were small.

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.

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. A single field study was conducted in 2000 at the Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of three dates of irrigation termination on the yield of 13 Upland cotton varieties. Planting date was 6 April (668 HU/Jan 1 86/55° F thresholds). Three dates of irrigation termination (IT1, IT2, and IT3) were imposed based upon crop development into cutout. The earliest irrigation termination date, IT1 (24 July) 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 was 17 August, and provided one additional irrigation over an optimal point for the first cycle fruit set and two irrigations beyond IT1. The final (IT3) date was 15 September, which was staged so that soil moisture would be sufficient for the development of bolls set up through the last week of September thus providing full top-crop potential. Lint yield and micronaire results revealed significant differences among the IT treatments. Micronaire and lint yield values increased with later IT dates.

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.

Nine defoliation treatments based on defoliating agents that are in use in the area plus two additives (compounds A, B) 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. One of the additives enhanced the early defoliation effectiveness of chlorate, the other additive enhanced the effectiveness of Ginstar throughout the defoliation process. More studies will be needed before recommendations can be made.