A field study was conducted at the Maricopa Agricultural Center to determine the influence of nitrogen fertility level on the effectiveness of defoliants for short-season cotton production. Increasing the nitrogen fertility level from 30 to 130 lbs N/A decreased lint yields from 3.2 to 26 bales /A. High residual soil N favored the use of a low N fertility rate. Defoliation treatments were most effective at the 30 lbs. N/A fertility level. Increasing the application rate of Dropp from 0.2 to 0.4 lbs. a.i./A increased the percent defoliation. There was a significant linear decrease in the effectiveness of defoliants as the petiole NO₃-N content increased from 300 to 7000 ppm.

A single field experiment was conducted in 1990 on a grower cooperator field to evaluate the response of a full season maturity type of Upland Cotton (DPL 90) to three dates of irrigationtermination. The crop was planted 26 and 27 of March, managed uniformly in all respects until August 1 when earliest irrigation termination wsa imposedThe dates for the second and final irrigationtermination treatments were 15August and 15 September. Each irrigationtermination treatments were given an additional 8 acre inches of water (approximate). Harvest results revealed no significant differences in lint yield on the first two dates but the last date yielded 110 pounds more. All plots received a 2 inch rain 18 August.

Five 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 1990 for treatment comparisons. However, it appears that consistencies in the effectiveness of several treatments for Pima defoliation offer a basis for recommendations across the state.

Arizona Cooperative Extension produced and distributed weather -based Planting Date and Cotton Development Advisories for 8 cotton production areas (Marana, Litchfield Pk, Pinal Co., Parker, Safford, Yuma Valley, Dateland and Aguila) in 1991. Planting Date Advisories were distributed from mid - February through the end of April and stressed 1) planting full season cotton varieties according to heat unit accumulations rather than calendar date and 2) the importance of soil temperature to good germination. Cotton Development Advisories were distributed from early May through mid- September and provided growers updates on crop development, insects, weather and agronomy. The Cotton Advisory Program will continue in 1992 with the major change being an expansion in coverage to include Paloma, Queen Ck, and Mohave Valley.

A replicated field study was conducted at the Maricopa Agricultural Center in 1991 to investigate the effect of plant population density on Pima S-6 lint yield. Treatments ranged from a low of 10,465 plants per acre to a high of 65,000 plants per acre. There were no significant yield differences observed with populations between 17,000 plants per acre and 65,000 plants per acre. Significant yield decreases occurred when populations were reduced below 17,000 plants per acre.

A field study was conducted at the Maricopa Agricultural Center to evaluate the effectiveness of selected defoliant treatments on Pima and Upland cotton under warm and cool weather conditions. In September tests, no defoliant treatment was effective in a single application. Upland cotton that was injured by frost in late October was difficult to defoliate in November tests. Pima cotton exhibited less frost injury than Upland and all defoliant treatments resulted in good defoliation in November.

A field study was conducted at the Marana Agricultural Center to evaluate the effectiveness of ground rig applied defoliant treatments on Pima and Upland cotton under cool weather conditions. Defoliants were slow acting at this location, however, all chemical treatments tested resulted in good defoliation 14 days after application.

A heat-unit-based planting window was introduced in 1991 as a means of reducing early season problems with pink bollworm (PBW). Growers were encouraged to plant full season varieties when the annual heat unit (HU) accumulation ranged between 600 and 900 -- a window designed to ensure 75% suicidal emergence of PBW yet maintain acceptable yield levels. New research findings and a reexamination of past PBW emergence studies now support making an adjustment to the planting window. For 199Z the recommended planting window is 450 - 700 HUs after January 1.

Five field experiments were conducted at three locations in 1991 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 2 April in the Yuma Valley (150 ft. elevation) to 14 May at Marana (2,000 ft. elevation). Dates of irrigation termination ranged from 8 August in the Yuma Valley to 24 September at Maricopa. Planting date was commonly a significant effect in these experiments, particularly with Pima cotton. Irrigationtermination results over three locations and three seasons show increases of approximately 50 to 100 lbs. lint /acre by extending later irrigations.

A field experiment was conducted in Yuma, Arizona to evaluate the effects of planting date on cotton yields. Six Upland varieties were planted on 3 dates from 15 March to 24 April in 1991. Significant differences were found among varieties at the first planting date (15 March) with full season varieties yielding higher than medium and short season varieties. No differences were found among varieties at planting dates 8 April and 24 April. Significant differences were found among planting dates for all varieties. Weather conditions in March were abnormally cool and may have negatively influenced yields from the first planting date.