A field trial was conducted during the 1992 & 1993 growing seasons to evaluate the activity of Cytokin and Pic applied alone or in combination to short staple cotton. The Cytokin treatment significantly increased tint yield over the other treatments in 1992. There were no statistically significant seed cotton differences between the non - treated check and any treatment in 1993. Fruit retention remained high throughout 1992 and very high throughout the 1993 season. Under high fruiting conditions, use of a plant growth regulator would not normally be recommended.

The effects of late -season Palm on the growth characteristics and yield of Upland cotton was examined in this study. Three treatments were imposed late-season (3447 HUAP), 1, a check plot, receiving no Pix™, 2 receiving 0.75 pt/acre, and 3; receiving 1 pt/acre. The imposed treatments did not have a statistically significant effect on plant growth characteristics or earliness nor were there any significant overall yield differences detected among treatments.

A field experiment was conducted at the UA Maricopa Agricultural Center (MAC) to determine the fruiting distribution patterns of two commonly grown Upland cultivars, DP 33b and DP 5415, and one American Pima cultivar, Pima S-7. Results indicate that cotton plants (G. hirsutum L. and G. barbadense L.) produce total yield at fruiting branches one through 18, with the majority of yield occurring at fruiting branches one through 12. Among fruiting branches one through 12, the majority of yield is occurring at fruiting positions one and two. These results indicate that the bulk of the yield is produced early in the season and declines as the season progresses

A series of boll measurements were taken at numerous locations across the state in 1997 in an attempt to continue to develop a yield prediction model that began in 1993. Results from 1995 showed the strongest relationship between final open boll counts and yield. Based on these results, data was collected in 1997 from several locations around the state. Boll counts were made just prior to harvest and then correlated to yield. Results showed that a good estimate for lint yield could be obtained using the factor of approximately 13 bolls/row-ft./bale of lint for Upland cotton on 38 to 40 inch row spacings.

Two PIX experiments were conducted on commercial cooperator sites in Waddell and Buckeye, Az in 1997 to evaluate the validity of the published University of Arizona (UA) PIX application guidelines for Bt cotton. Experimental treatments consisted of an untreated check, a calendar based application schedule (early bloom, peak bloom, cutout), and a feedback approach using plant growth measurements based on the UA PIX guidelines (height:node ratio, fruit retention). There were no significant yield differences at the Waddell site where height:node ratios and fruit retention values were above the optimum baseline season long, conditions not supportive of PIX applications. There was a significant yield decline at the Buckeye site between the untreated check and the calendar based treatment. Due to low plant vigor season long , there were no feedback based PIX applications. PIX applications under low vigor conditions can further compromise plant vigor and ultimately yield. The UA PIX application use guidelines are valid and should be used for both Bt and non -transgenic Upland cotton varieties.

Summaries of cotton crop phenology, as a function of heat units (HU, 86/55°F limits) have been developed across a wide range of production conditions in Arizona. Basic phenological events such as the occurrence of pinhead squares, squares susceptible to pink bollworm, and first bloom are described in terms of HU accumulations since planting (HUAP). Fruit retention guidelines and height: node ratios, which measure a crop's vegetative /reproductive balance, are developed as a function of HUAP. Similarly, the rate of canopy closure is described in terms of HUAP. The use of the number of nodes above the top white bloom to the terminal (NAWB) is developed as a measure of a crops progression towards cut-out. Also, the expected ranges of HU's accumulated since planting that are required to accomplish crop cut-out are shown for Upland and Pima cotton.

Several plant growth regulators were applied to DPL 5415 cotton to evaluate effectiveness on cotton lint yield. Growth regulators applied in small amounts over multiple applications early in the growing season reduced yields compared with the check while a single application applied at full-bloom slightly increased lint yields. High night time temperatures from late July into early September were detrimental for cotton production. Increased squaring of early season applications compared with the check may have resulted in reduced yields due to increased stress from temperatures and/or nutrient availability. Increased stress in the early treated (more fruit) plots may have had greater fruit abscission.

Cotton crop response was evaluated using the growth regulator FIX in a conventional liquid formulation compared to an equivalent rate of a newly developed dry flowable (DF) formulation. The DF formulation will be available in 1996 in water soluble packets with each 57 gram packet the equivalent of one pint liquid PIX. Both formulations regulated plant height and height:node ratios equally.

All plant growth regulators and nutritional products applied to Pima S-7 cotton during bloom economically increased lint yields, with increases ranging from 80 - 261 lbs. /acre. Greatest increase was noted with Boll-Set Plus, a product that contains raised levels of calcium and zinc. Cytokin and Boll -Set Plus significantly increased yields at one location. A lint yield increase of approximately 40 lbs/acre was noted when Tech-Flo Alpha was added to Cytokin. A single application of Foliar Triggrr resulted in equal yields as two applications of the Cytokin plus Tech-Flo Alpha.

Methanol, Cytokin, Cytoplex, PGR IV and Foli-Zyme plant growth regulators were tested on long and short staple cotton on the Safford Agricultural Center in 1995. It was a follow up study on Methanol, Cytokin and PGR IV and a first time look at Cytoplex and Foli-Zyme. Trends toward increased lint yield were seen with Cytokin and Cytoplex with the other treatments yielding near or below the untreated check Some increase in maturity was seen on the short staple plots by all of the treatments. Some differences in HVI data were also observed.