A field study was conducted at the Maricopa Agricultural Center to determine the effect of nitrogen fertility level on the effectiveness of PIX and defoliants for short- season - cotton production. Increasing the nitrogen fertility level from 90 lbs N/A to 240 lbs N/A increased lint yields from 2.23 to 3.14 bales/A, respectively, in a 157-day growing season. FIX treatments did not promote earliness, and resulted in yield reductions. Increasing the application rates of Dropp from 0.1 to 0.2 lbs a.i./A and Def-6 from 0.75 to 1.13 lbs a.i./A resulted in increases in leaf drop. There was a significant linear decrease in the effectiveness of defoliants as the petiole NO3 N content increased from 850 to 2450 ppm.

A field experiment was conducted in Yuma, Arizona, to evaluate the effects of planting date on cotton yields. One Pima and the Upland cotton varieties were planted on four dates from 23 February to 5 April. DPL-90 produced the highest yield (1760 lbs lint acre⁻¹) at the second planting date (9 March). The lowest yields, for all varieties, resulted from the latest planting date (5 April). The greatest reductions in yield when comparing an early planting date to the latest planting date, were observed for DPL-90 and Pima S-6. However, in spite of the reduction in yield, DPL-90 was the highest yielding variety at the latest planting date.

Three field experiments were conducted in 1989 in Arizona to evaluate the response of Upland and Pima cotton to two dates of planting and two dates of irrigation termination. Planting dates ranged from as early as 22 February in the Yuma Valley (150 ft. elevation) to 4 May at Marana (2,000 ft. elevation). Dates of irrigation termination ranged from 27 July in the Yuma Valley to 8 September at Maricopa and Marana. Based upon the final lint yield, planting date provided a significant main effect within two of the three experimental locations (Yuma Valley and Marana). At the Maricopa location, there was a significant effect on yield due to date of irrigation termination with both 30-inch- and 40-inch-row Upland cotton experiments, resulting in differences of 167 and 157 lbs. lint /acre, respectively, by extending two irrigations (approximately 12 acre inches) past 10 August to 8 September. The Pima experiment at Maricopa was similar with a significant (P <0.05) response to two additional irrigations (approximately 12 acre-inches) of 184 lbs. lint /acre. Return from additional lint yield must be considered against additional costs (water, insect control, etc.), as well as possible quality losses from insect infestations.

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 short season cotton. Irrigation termination dates of 11, 18 and 24 August were used to achieve different levels of water stress at the time defoliants were applied (1 September). Irrigation termination dates had little effect on the response of cotton to defoliants. Def-6 at the lowest rate tested, 0.75 lbs a.i./A, was less effective in defoliating cotton with a 24 August irrigation termination date than cotton terminated earlier. Dropp resulted in higher defoliation percentages and 30% fewer unopened bolls at harvest than Def-6. Although the irrigation termination dates provided a range of CWSI values at the time of chemical termination, no clear relationship was found between CWSI values and defoliation percentages. Short season cotton (149 days) produced 3.2 bales of lint/A compared to 4.4 bales for a full-season crop (208 days).

Four field experiments were carried out in several representative cotton producing areas of Arizona to evaluate the effectiveness of a number of defoliation treatments on Pima cotton. Variable conditions were encountered among the experimental locations in 1989 for treatment comparisons. However, it appears that consistencies in the effectiveness of several treatments for Pima defoliation offer a better basis for recommendations across the state.

A single field experiment was conducted in 1989 to evaluate the relationship of crop water status on Pima cotton defoliation by use of a crop water stress index (CWSI) as estimated by infrared thermometry. The entire study area was given the last irrigation uniformly on 24 August, and 20 row plots were outlined for the arrangement of three treatments in a randomized complete block design with three replications. Treatments consisted of making defoliant chemical application at three different targeted CWSI levels (0.40, 0.60, and 0.85). All defoliant treatments consisted of Dropp plus Accelerate (0.4 lb. and 1.5 pt. of material/acre, respectively) applied with a ground rig applicator. Results indicated no distinct advantage in terms of percent defoliation as a function of lower CWSI levels at which defoliants were applied. The defoliations made at 0.40 CWSI did result in more regrowth after 14 and 21 days. It appears from this test that Pima plants will defoliate satisfactorily with proper chemical treatments up to CWSI levels of 0.80. Further desiccation of the crop results in very erratic CWSI readings, resulting in difficulties in applying this technique to defoliation management. It does appear, though, that Pima cotton defoliation can be accomplished when CWSI readings are between 0.5 and 0.8 without substantial regrowth problems, providing precipitation or irrigation events do not occur.

A field study was conducted at the Maricopa Agricultural Center to evaluate the effectiveness of experimental defoliants and adjuvants on DPL 90cotton. None of the defoliation treatments tested were effective in September when air temperatures were above 100° F. Several chemicals gave 80% or higher defoliation in early October when temperatures were in the low 90s. The experimental defoliant SN 597 NA218 appears to have promise as a late-season defoliant for DPL 90 cotton.

Four flea experiments were conducted in 1990 in Arizona to evaluate the response of Upland and Pima cotton to dates of planting and dates of irrigation termination. Planting dates ranged from as early as 27 February in the Yuma Valley (150 ft. elevation) to 8 May at Marana (2,000 ft. elevation). Dates of irrigation termination ranged from 18 July in the Yuma Valley to 8 September at Maricopa and Marana.

A field study was conducted at the Maricopa Agricultural Center to evaluate the effectiveness of selected defoliant treatments on Pima cotton under warm and cool weather conditions. Dropp was effective as a one application defoliant in September when air temperatures were in the high 90's. In October, when night temperatures were lower, no defoliant tested was effective in a single application.

A field study was conducted at the Marana Agicultural Center to evaluate the effectiveness of selected defoliation treatments on Pima cotton under cool weather conditions. Defoliants were slow acting at this location, probably due to cool night temperatures and dry field conditions. The combination Dropp + Def 6 + Accelerate gave good defoliation results 18 days after application. The experimental defoliant SN 597 NA 243 shows promise as a defoliant for Pima when temperatures are cool.