Harvest aid combination and application timing effects on lint yield and fiber quality
Kelley, Mark S.
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Since the advent of harvest aids, upland cotton (Gossypium hirsutum L.) producers in the Texas High Plains have benefitted from early crop termination and timely harvesting. Cotton produced on the Texas High Plains can typically be characterized as non-rank, irrigated, short-season stripper-harvested types. Leaving a crop in the field until a freeze can reduce lint yields and quality due to inclement weather skuations. These losses can often be reduced when harvest aids are utilized. The objectives of this research were to determine how early a crop could be terminated without adversely affecting lint production and quality. Replicated field experiments were conducted at 3 locations (1 in 1998 and 2 in 1999). Treatments consisted of (1) ethephon [(2-Chloroethyl) phosphonic acid] + tributes (S,S,S-Tributyl phosphorotrithioate), (2) thidiazuron/diuron [N-phenyl-N'-l ,2,3-thidiazol-5-ylurea/3-(3,4- ichlorophenyl)-1,1-dimethylurea] alone and (3) ethephon + thidiazuron/diuron. These were all applied at 0-10, 30 and 60% open boll (OB) and terminated with paraquat (1,1' -dimethyl 4,4' -bipyridinium dichloride) at 7 to 14 days after 60% OB applications. In addition, two untreated controls (one terminated with paraquat and one left to freeze) were evaluated. Data from these studies indicate that yield can be adversely affected by early applications of harvest aids. Yield results from the 3 locations indicate chemical treatment regime had no significant effect on bur cotton, lint and seed yields. However, application timing had a significant effect on yields. Extremely early (0-10% OB) applications of harvest aids significantly reduced yields. The 30% OB application timings at Halfway and Petersburg, however, had no effect on yield then compared to the 60% OB application timings. This is due in part to the crop and environmental conditions at time of application. Certain HVI fiber properties may also be adversely affected by early harvest aid applications, including reductions in micronaire values. Micronaire values were reduced by the 0-10% OB applications at Olton and Petersburg. Chemical treatment regime, however, did not significantly impact micronaire at any location. Although lint quality may be influenced by application timing of harvest aids, those influences may not affect final lint value. The use of ethephon may reduce APIS measurements of fineness and fiber maturity values while in turn increasing immature fiber content (IPC) as was observed at Halfway in 1999. Application timing also had an impact on APIS measurements of fineness, IPC, and maturity ratio. The results from APIS measurements helped explain the reductions in micronaire values at Petersburg. In conclusion, producers on the High Plains of Texas would benefit from waking until 60% of harvestable bolls are open before applying harvest aids under normal conditions. Should the need arise to apply harvest aids at earlier timings, 30% OB applications may prevent significant yield and fiber quality losses if detrimental weather, such as an early freeze, is expected. This however may in itself cause yield losses if the condition of the crop is not conducive to harvest aid applications.