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.

The old standar4 1517-75, was the best yielding variety in 1989, yielding over three bales of lintper acre. 1517-77BR, which yielded well in 1987 and then dropped off a bit in 1988, carne in second and an experimental, 6658 came in third. The touted New Mexico star, 1517-88 came in fourth followed closely by California's Prema. Eight of the 10 varieties tested yielded over 2.5 bales per acre. More than normal heat units coupled with good management practices brought the highest yields yet recorded in a University cotton variety trial in Cochise County.

Forty-nine, short- staple varieties and Pima S -6 were grown in a replicated trial on the Safford Agricultural Center in Graham County. Most of the varieties were commercially available in the Cotton Belt, however, a few experimental varieties from the New Mexico acalas and from Delta Pines were included. Weather conditions were favorable through most of the year and the cotton produced well. Fifteen varieties produced more than 4000 pounds of seed cotton per acre, with the highest yielding variety producing 4759 pounds per acre. Delta Pine 77 was the highest yielding commercial variety but it was topped by an experimental New Mexico acala.

Short- staple variety trials were grown in two locations in Graham County in 1989. Exceptional weather conditions, coupled with good management practices, provided record cotton yields in the Safford valley. Delta Pine 77 was the highest yielding variety in the Thatcher location with a yield of 1740 pounds of lint per acre. An experimental acala from New Mexico came in second in this triad ahead of Delta Pine 90. Delta Pine 90 was the highest yielding variety in the Eden area with a yield of 1196 pounds per acre. Data on percent first pick plant height and plant populations are presented for each variety in each location. Graphs of heat units received each day throughout the growing season at the AZMET station on the Safford Agricultural Center are presented for 1988 and 1989.

Two short staple and one long staple variety trials were implemented in Greenlee County in 1989, with new varieties topping each trial. The most exciting new discovery was HS 46, which topped the competition in the short-staple trial by nearly 200 pounds of lint per acre. In the acala trial, the top four entries were composed of three New Mexico experimentals and Prema from the San Joaquin Valley. Any one of these acalas could become the new standard for the valley. P-69 in the long staple cotton trial yielded over 850 pounds of lint per acre and topped the S-6 yield by 25%. The testing program in Greenlee County is not only of benefit to the cotton producers and related agri-businesses in southeastern Arizona, but also to southwestern New Mexico.

The standard variety DPL 61 yielded higher in this trial. M-5, a California acala type was tested for the first time.