A series of boll measurements were taken at two locations in 1994 on 5 different varieties in an attempt to develop a yield prediction model. Measurements were taken in strip plot variety trials at Maricopa Agricultural Center and Marana Agricultural Center over a period of approximately 2 months from peak bloom through cut-out. Measurements taken included boll weight, boll diameter, bolls/meter, plants/meter, and final yield from each specific measurement area. Stepwise linear regression resulted in a yield prediction model expressing yield as a function of heat units accumulated after planting, boll diameter or boll weight, and bolls/meter.

Two field experiments were carried out in representative cotton producing areas of Arizona to evaluate the effectiveness of a number of defoliation treatments on Pima cotton. These experiments were conducted at Coolidge and Marana. The treatments employed principally consisted of relatively new materials available in Arizona, and were compared to current standard treatments. All treatments showed promise in terms of effectiveness and the results provide a basis for use recommendations in 1995.

Field studies were conducted at the Maricopa Agricultural Center to evaluate the effectiveness of selected defoliation treatments on Pima and upland cotton under warm and cool weather conditions. Air temperatures were high for tests conducted on 16 and 22 September and cool for tests conducted on 14 October. In September tests, Pima cotton was more susceptible to leaf desiccation after applications of defoliants than upland cotton. Single applications of Ginstar or Dropp + Def gave good defoliation in September tests. In October, Pima cotton was effectively defoliated by chemical treatments but a single application of defoliants did not provide acceptable defoliation of upland cotton.

Experiments were effected on both Pima and upland cotton to compare the defoliation effects of different rates of Ginstar, Ginstar + Prep and sodium chlorate with an untreated check. Weather conditions after treatment applications were recorded and observations taken after one week and two weeks. Grab samples were taken from the picker to determine percent trash and to run HVI analyses.

Preharvest applications of Roundup improved defoliation and regrowth suppression when used in conjunction with an application of Dropp +Def on Upland cotton in experiments conducted in Buckeye, Maricopa, and Queen Creek, AZ. However, all treatments used provided commercially acceptable defoliation. Preharvest Roundup applications made about two weeks (or one irrigation interval) before the application of Dropp +Def did not reduce seed cotton yields, lint yields, or affect color-grade and fiber characteristics.

A study was conducted at the University of Arizona Maricopa Agricultural Center, Maricopa, AZ in 1994 to determine the influence of plant water status at the time of defoliation on effectiveness of defoliants and yield of Pima cotton. Several irrigation termination dates were used to achieve different levels of plant water stress at the time defoliants were applied. A single application of defoliants did not provide adequate defoliation under the conditions of this test. The earliest irrigation termination date resulted in the highest defoliation percentage. High CWSI values at the time defoliants were applied were related to the highest defoliation percentages, but were not necessarily related to satisfactory defoliation. The CWSI appears to have limited value as a guide to determine when to defoliate Pima cotton.

Field studies were conducted at the Maricopa Agricultural center to evaluate the effectiveness of Accelerate when used in combination with other defoliants. In addition, an experimental compound was tested as a boll opener. Air temperatures were very high at the time these tests were conducted and most defoliant treatments caused desiccation of Pima leaves 7 days after treatments were applied. Several treatments did result in acceptable defoliation of Pima cotton 14 days after application. In the upland test, Ginstar used alone resulted in higher defoliation percentages than any combination of defoliants. Boll opener treatments had no effect on boll opening of Pima or upland cotton. In these tests, there were no differences among treatments in lint yield or fiber properties.

A single field experiment was conducted at Marana Agricultural Center (2000 fl elevation) to evaluate the response of one Pima (G. barbadense L) and two Upland (Gossypium hirsutum L.) cotton varieties to three different planting dates. Planting dates ranged from 12 April to 16 May. In general there was decreasing lint yield with later planting dates.

Four varieties each of Long Staple and Short Staple cotton were tested over five and four dates of planting, respectively, in this study. The first date of planting for the Long Staple cotton was pushed up to the 18th of March because planting is now legal in Graham county as early as March 15th. The latest planting was May 13th. Cultivars of differing maturities were tested for both long and short staple cotton to determine their optimal planting time. Many agronomic and hvi values were evaluated to determine the effect of different planting dates

In the latter part of the 1997 season (August) many fields across Arizona, from Marana to the Mohave Valley, were experiencing premature senescence. In an effort to evaluate the conditions leading to the symptoms and to possibly determine the causes, an extensive series of field examinations were conducted in a number of representative fields in central Arizona. Soil samples were taken from selected fields that ranged in expression of the symptoms from very light to severe. Complete analyses of the soil samples were conducted. Plant tissue samples were also collected and analyzed for plant nutrient levels. No absolute causal agent was identified. However, a factor believed to be of significance was that of low soil K levels, where many of the fields expressing the most severe symptoms also had low soil K levels. It is also important to consider the fact that plants exhibiting K deficiency are very similar in appearance to plants affected by Verticillium wilt, which also appeared to be a primary or contributing factor in many cases.