A field study was initiated in the summer of 1993 to investigate the effect of increased night temperatures on cotton reproductive development. DPL 5415 was planted on May 10. Treatments consisted of two temperature regimes placed in a completely randomized design with four replications. The two temperature treatments were initiated at first bloom and treatments terminated after 6 weeks. Cotton grown under ambient night temperature served as the control treatments while plants where the infrared radiation balance was modified to increase the nighttime foliage temperature served as the high night temperature treatment. This study showed that increasing the nighttime foliage temperature of cotton reduced vegetative dry matter production, plant height, and fruit retention. The photosynthetic capacity of the two treatments was not significantly different, suggesting that increased respiration at these higher nighttime foliage temperatures may be responsible for the reduction in assimilated carbon which contributed to the poor fruit retention.

Boll maturity dates and the number of days after flowering for a boll to reach physiological maturity were estimated for six representative flower dates: 15 July, 29 July, 12 August, 26 August, 9 September and 23 September. Estimates were developed for 28 locations using historical heat unit (HU) information using the assumption that 600 HUs are required after flowering for a boll to reach physiological maturity. The results are presented in both tabular and graphical forms.

The terminal of a cotton (Gossypium spp.) plant controls the growth of lower vegetative branches through the production of hormones. If the terminal is damaged then the lower vegetative branches will begin to grow and produce new mainstems. The objective of this study was to determine what delays, if any, are caused by damage to the terminal meristem. Three identical experiments (differing only by their planting date) were conducted in the greenhouse in which Upland (G. hirsutum L., var. DPL 5415) cotton was planted in 24 pots and allowed to grow until the majority of the plants reached the four true -leaf stage. At that point half of the plants had their terminals removed. Twice weekly series of plant measurements were recorded for each plant in the study. Measurements taken included the number of mainstem nodes, plant height, node of the first fruiting branch (FFB), days after terminal removal (DATR) until the appearance of the FFB, node of the first bloom, and DATR until the appearance of the first bloom were recorded. Removal of the terminal significantly increased the node of the FFB, the node of the first bloom, and the occurrence of each of these by 7 to 8 days. Regression analysis was used to model plant height and the accumulation of mainstem nodes as a function of DATR. Results showed that plants with terminals removed did reach the same height as the control group. However, the plants with their terminals removed never accumulated as many mainstem nodes as their counterparts in the control group.

Two field experiments were conducted in 1993 in Arizona to compare a scheduled approach (based on stage of growth) versus a feedback approach (based on vegetative status) to mepiquat chloride (PIX™) applications on Upland cotton (Gossypium hirsutum L.). PIX feedback treatments received no PIX applications due to plants lacking vegetative tendencies based upon height:node ratios (HNRs) and established baselines. Scheduled PIX applications ranged from 0.5pt. /acre to 0.75 pt./acre, and were applied at early bloom (approx. 1500 heat units after planting (HUAP), 86/55 °F threshold) and post early bloom (approx. 2000 HUAP). PIX treatments did consistently reduce plant heights compared to an untreated check. Statistically significant differences (P ≤ 0.05) in lint yield were observed among the treatments (feedback vs. scheduled)at the Safford location only. Evidence from these studies do reinforce the use of a feedback approach from the standpoint of conserving inputs and maintaining optimum growth control.

The effects of foliar applied methanol on Upland cotton were measured in a large field study in Phoenix, AZ. An untreated check was compared to weekly applications of 30% methanol, 30% methanol plus 1% Urea and 0.1 % Fe EDTA, and 1% Urea and 0.1% Fe EDTA. Plant growth and development, photosynthesis, transpiration, soil water use and lint yields were measured. There were no differences in any of the measured variables between treatments.

A study was conducted at the University of Arizona Maricopa Agricultural Center, Maricopa, AZ in 1993 to determine the effect of foliar applications of methanol on cotton physiology, growth, yield and whitefly infestation. Six applications of a 30% methanol solution during bloom had no effect on plant height, boll weight, lint yield or earliness of Pima S-7 (Gossvpium barbadense L.) or upland DP5415 (Gossvpium hirsutum L.) cotton. No effect of methanol on photosynthesis or photorespiration was observed. A significant reduction in sweetpotato whitefly nymph population occurred on DP5415 cotton seven weeks after methanol treatment began. This study provided no evidence that methanol can be used to improve cotton production.

Results from several tests both on the Safford Agricultural Center and off are reported on in this paper. Methano4 Cytokin, X-Cyto, Temik and Amplify-D treatments results are included and discussed.

Six commercial scale field studies were conducted from 1991-1993 to further evaluate and predict Upland cotton yield and development responses to PIX application timing as a function of cotton growth and condition. Treatments imposed intended to further clarify some response trends observed in previous years of field studies. Treatments were all at the maximum label rate of one and one half pints with application timing the main variable. Timing was based on heat unit accumulation and resultant growth stage since date of planting. Two of the six studies resulted in significant lint yield increase of roughly one hundred pounds across all PIX treatments in contrast to the untreated check. The two studies which resulted in lint yield increases both had height: node ratio measurements in excess (vegetative) of previously defined guidelines.

The commercial product PGRIV was tested in small plots on cotton at the Maricopa Agricultural Center. Multiple foliar applications of PGRIV had no significant effect on lint yield or fiber properties of DP5415 or Pima S-7 cotton.

Methanol, Cytokin and PGR IV plant growth regulators were tested on long and short staple cotton on the Safford Agricultural Center in 1994. It was a follow up study on Methanol and Cytokin and a first time look at PGR IV.