Three upland cotton varieties (Stoneville 506, Deltapine 20, and Centennial) were planted on four dates in 1987 at the Maricopa Agricultural Center and observed for flowering, boll opening, and lint yield. Results from 1985-1987 are being used to develop heat unit models for the timing of these events.

Wide variations existed in the performance of cotton varieties over the five planting dates among three locations over three years. However, on the average, DP 77 performed best when planted between 27 March and 22 April at Maricopa and Marana. DP 90 was best for April and early May plantings at Safford. Stoneville 506 and DP 50 were among the best for May plantings. DP 20 Stoneville 112, and DP 50 averaged best for early June plantings, except Germain 510 was superior at Safford.

A field study was carried out to test the effectiveness of several defoliation treatments on Upland cotton in Pinal County. Three defoliation treatments were utilized. Results showed no significant differences among treatments in terms of percent leaf drop estimates taken seven and 14 days after initial application. Subsequent applications of defoliant materials were made to accomplish satisfactory levels of defoliation prior to harvest.

This test was conducted on the LDS Church Farm in Marana to determine whether ripping after the Uprooter-Shredder-Mulcher (USM) benefits yields. The three treatments were rip furrows only, rip -beds only, and no ripping after the USM. Depth of water penetration was measured after the preplant irrigation; no significant differences were observed between the treatments. Differences in lint yields were not statistically significant, although average lint yields for the ripped treatments were higher.

Cotton growers began cotton harvest earlier in 1987 than during the previous three years, but they fell behind the other years by December first. Rainfall in late October, particularly November 2, slowed harvest and reduced quality of cotton dramatically in some operations.

Planting Pima S-6 at 12-day intervals starting April 2 produced more than 70 pounds of lint loss for each delay in planting.

Double cropping barley and cotton, using a system of controlled traffic tillage, was compared to conventionally tilled, full-season cotton. In this test, the yields of the barley and late planted cotton were too low to be competitive with the full season cotton.

A field study was conducted at the Maricopa Agricultural Center to determine the influence of plant water stress on the effectiveness of defoliants and yield of cotton. Irrigation termination dates of 12 August, 24 August, and 8 September were used to achieve different levels of plant water stress at the time defoliants were applied (22 September). The defoliants tested performed well on cotton, which had termination irrigations in August. Def 6 was not as effective as other defoliants in defoliating plants with an 8 September termination irrigation, unless used in combination with Prep. Cotton with an 8 September termination irrigation produced lint yields 9% higher than cotton with August irrigation termination dates.

Field experiments were carried out at 4 locations in Arizona to evaluate the effects of planting date on the lint yield of several varieties of cotton. One pima and eleven upland varieties were planted on 5 dates at 2 locations and 1 pima and nine upland varieties were planted on 5 dates at a third location. At a fourth location, 1 pima and 3 upland varieties were planted on 4 dates. General trends in lint yields indicate an advantage in yield potential from full- season type varieties, particularly when they are planted early. Full-season varieties, however, diminish rather quickly with regard to yield potential, when planting is delayed in comparison to varieties that are considered mid-or shorter-season varieties.

Irrigation termination trials were continued in 1988 to evaluate a newer, popular upland variety and pima S-6. Irrigation in the first week of September increased the yield of a May planting of DP 77, but not of two trials in 1988 with early April planting dates. A March planting of pima S-6 failed to respond to a 10 September irrigation on Coolidge sandy loam.