Effects of harvest aid materials and timing on planting seed quality

Abstract

The High Plains of Texas is a 22-county region that grows approximately 1.6 million hectares of upland cotton (Gossypium hirsutum L.) each year. In recent years, the cotton market has changed both domestically and overseas, and cotton growers are searching for new methods to improve crop yields. One method of increasing crop yields is to plant quality seed that is known to be vigorous. This method increases field germination and reduces the need to replant. Another method of preserving yields and quality is to apply harvest aid chemicals, which are used to prepare the cotton for an earlier harvest. With the changes in the industry, cotton growers have dramatically expanded their use of harvest aid chemicals in the last few years. Timely applications of these harvest aid chemicals are essential in avoiding premature loss of yield and seed quality. The objective of this study was to investigate how applying specific harvest aid chemicals, at potentially sub-optimal 10% and 30% open bolls, may affect cotton seed quality and vigor. This knowledge could facilitate even earlier harvest dates, thereby possibly increasing growers. and seed companies. profits. In this project, harvest aid chemical treatments included ethephon (Prep®) plus tribufos (Def®), at 0.84 kg ai ha 1 each, and dimethipin (Harvade®), at 0.34 kg ai ha-1 and 0.51 kg ai ha-1 rates. These treatments were compared to an untreated check that had no chemical application and were left to the freeze. Also included was a paraquat (Cyclone®) control that had no earlier chemical application; however, it was terminated by a paraquat application at 0.62 kg ai ha-1 at the same time the earlier chemical treatments were terminated (about 14 days after initial treatment). Four replicates were used in all field and laboratory studies. At harvest, a stratified boll sample was collected from each treatment and from the two controls. In each plot, the cotton plants were divided into upper, middle, and lower sections (strata). From each plot, fifty bolls were harvested from each stratum. After ginning, seed quality from these stratified sections was evaluated using the Cool-Warm Vigor Index (CWVI) and seed index. The CWVI uses the combined results from the Warm Germination Test and the Cool Germination Test. The seed index is determined by the weight, in grams, of 100 delinted seeds. The study was conducted at two locations in 1997 (Lubbock and Lamesa) and at three locations in 1998 (Lubbock, Seminole, and Olton). Data were analyzed by location using the GLM and Mixed Procedures in SAS. The untreated check was not necessarily the best method to use for chemical effect comparisons, possibly due to issues including maturity and preharvest losses. Therefore, the paraquat control generally produced more consistent results for comparing other chemical treatment effects. Stratified sampling results indicate, in general, that CWVI and seed index were adversely affected by the harvest aid chemicals at both timings of application. Dimethipin rates and treatments were generally not as detrimental as the ethephon plus tribufos to seed index. Lint yield results indicated that significant differences among treatments were noted at four of five locations. In general, the more aggressive ethephon plus tribufos treatment reduced lint yield and micronaire when applied at 30% open bolls or less. Even the less stringent dimethipin reduced yield and micronaire at some sites. Results from this research indicate that significant reductions in seed quality (CWVI and seed index) can be caused by premature applications of certain harvests aid chemicals. There was no indication that the use of any of the treatments caused the enhanced movement of photosynthates into the seed which might result in a benefit of higher vigor or weight. In fact, quite the opposite was noted.