A single field experiment was conducted near Coolidge, AZ in 1995 to evaluate the effectiveness of a number of defoliation treatments on Upland cotton (var. DPL 5415). All treatments consisted of materials commercially available in Arizona, and each showed promise in terms of overall effectiveness. Results do provide reinforcement for current defoliation guidelines for Arizona which recommend using low rates (relative to the label ranges) under warm weather conditions, and increasing rates as temperatures cool.

Twelve 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 series of boll measurements were taken at several locations across the state in 1995 in an attempt to develop a yield prediction model. Measurements were taken out of two strip plot variety trials at the University of Arizona Maricopa Agricultural Center and in the Coolidge area, and also out of two commercial fields in Buckeye and Paloma Ranch over a period of approximately 2 months from peak bloom through cut-out. Data analysis revealed a best fit model that included seedcotton yield as a function of boll count, boll size, boll diameter, and heat units accumulated after planting (HUAP). A series of open boll counts were also taken from over 120 experimental units across the state within one week of harvest. The data revealed strongest relationships between final open boll counts and yield.

Arizona Cooperative Extension generates and distributes weather -based Planting Date and Cotton Development Advisories for 14 cotton production areas (Marana, Laveen, Paloma, Litchfield Pk., Pinal Co., Parker, Mohave Valley, Queen Creek, Safford, Yuma Valley, Aguila, Cochise Co., Greenlee Co. and Harquahala). Planting Date Advisories are distributed from mid -February through the end of April and stress 1) planting cotton varieties according to heat unit accumulations rather than calendar date and 2) the importance of soil temperature to good germination. Cotton Development Advisories are distributed from early May through mid - September and provide updates on crop development, insects, weather and agronomy. The Cotton Advisory Program will continue in 1996 and growers may obtain advisories by mail or fax from the local county extension office, and by computer from AZMET or the University of Arizona College of Agriculture World Wide Web Page. Major program changes planned for 1996 include 1) adjusting the Crop Development Advisories to reflect the revised legal first planting dates in low elevation production areas and 2) the addition of an advisory for Harquahala.

Defoliation tests were conducted on upland cotton at the Maricopa Agricultural Center to evaluate rates of Ginstar and tank mixes of Ginstar with Def, Prep, and spray adjuvants. In September when temperatures were high, good defoliation was obtained 14 days after treatment using Ginstar at 0.094 lb. a. i./acre. As temperatures cooled in early October, a higher rate of Ginstar was necessary to achieve defoliation. Under very cool temperatures in late October and early November, the tank mix of Ginstar + Def generally improved defoliation over Ginstar used alone. Several adjuvants appeared to improve the effectiveness of Ginstar when temperatures were cool.

Arizona Cooperative Extension generates and distributes weather-based Planting Date and Cotton Development Advisories for 15 cotton production areas (Marana, Laveen, Paloma, Litchfield Pk., Pinal Co., Parker, Mohave Valley, Queen Creek, Safford, Yuma Valley, Aguila, Cochise Co., Greenlee Co., Harquahala and Wellton-Mohawk). Planting Date Advisories are distributed from shortly after legal first planting date until the end of April and stress 1) planting cotton varieties according to heat unit accumulations rather than calendar date and 2) the importance of weather conditions and soil temperature to good germination. Cotton Development Advisories are distributed from early May through mid- September and provide updates on crop development, insects, weather and agronomy. The Cotton Advisory Program will continue in 1997, and growers may obtain advisories by mail /fax from local extension offices or by computer from the AZMET computer bulletin board system or AZMET Internet Web Page (http://ag.arizona.edu/azmet). Major program changes planned for 1997 include 1) providing heat stress information on Crop Development Advisories and 2) the addition of an advisory for the Wellton-Mohawk area.

Three field studies were conducted in 1996 at the Maricopa (1,175 ft. elevation), Marana (1,974 ft. elevation), and Safford (3,000 ft. elevation) Agricultural Centers to evaluate the effects of three planting dates on yield and crop development for Upland and Pima varieties. Planting dates ranged from 19 March to 16 May and also 437-1199 HU /Jan 1 86/55° F thresholds). Crop monitoring revealed increased vegetative growth tendencies with later plantings. General trends also showed decreasing lint yield with the later plantings for all varieties at each location.

In 1996 transgenic Bt cotton was first grown on a commercial level in Arizona and the U.S. cottonbelt. Insecticidal properties of Bt varieties had been evaluated rather thoroughly in both the private and public sectors prior to commercial release. However, the agronomic characteristics had not been evaluated to any sufficient extent beyond the level of the developing companies. Lab and field tests were conducted in Arizona in 1996 dealing with the Delta and Pine Land Co. (DPL) companion varieties 5415/NuCOTN 33b (similar to 5415 but with the Bt gene) and 5690/NuCOTN 35b (with Bt gene). Most field comparisons were between 5415 and 33b. Lab and field studies revealed very similar agronomic characteristics between the companion varieties. No differences were detected with respect to heat tolerance, as determined by comparative fruit loss and abortion rates at the onset of the monsoon season. Only slightly higher vigor or growth rates were noted for 33b over 5415, which was considered to be negligible. Yield results revealed higher lint yields for 33b over 5415 in most cases. The difference in yields were attributed to pink bollworm infestations and damage, even when chemical control measures were being taken. It was concluded that 33b, as a transgenic version of 5415, is indeed very close to it's non-Bt counterpart.

A single field study was conducted in 1995 at the Marana Agricultural Center (2000 f elevation) to evaluate the effects of three planting dates on yield and crop development for one Pima and two Upland varieties. Planting dates ranged from 6 April to 18 May (469 -931 HU /Jan 1 86/55° F thresholds). Crop monitoring revealed vegetative growth tendencies with later plantings. General trends showed decreasing lint yield with the later (18 May) plantings for all varieties. Early plantings (6 April) however, for both Pima S-7 and DPL 20 resulted in slightly lower yields than the later two planting dates. This reduced yield for planting date 1 can be explained by extremely cool weather conditions which occurred immediately after planting and in-season fruit loss which impacted the final fruit retention levels.

Four varieties of Long Staple cotton were tested over three dates of planting in this study. Two later maturing varieties, Pima S-6 and Oro Blanco, and two earlier maturing varieties, Pima S-7 and Conquistador (OA 312), were planted at three dates ranging from early April to mid May to find the optimal planting times as well as the yield reduction effects of planting too late for a particular variety.