| Abstrakt: |
Proper timing of defoliation can significantly increase yields and quality. Methods currently used in North Carolina to time defoliation, are the percent open boll method (% OB) and the nodes above cracked boll method (NACB). It is generally safe to defoliate when the majority of the plants in a field are 60 % OB (Cotton Information, 2004). However, variability in crop development may alter this recommendation. Boll population may be at various stages of maturity near the time of harvest, due to the indeterminate growth habit of cotton (Stewart et al., 2000). Due to high early season square retention, in North Carolina, the majority of the crop is set over an 8 to 10 node horizon, which is closer in maturity than a crop set over 12 to 14 nodes, therefore may be defoliated earlier in terms of %OB and NACB (Stewart et al., 2000). Faircloth et al., (2004), found an increase in yield of 75 kg/ha across varieties, by delaying defoliation from 40 % OB to 60% OB, however UHM was unaffected by % OB changes, across varieties (Faircloth et al., 2004). In another study concerning defoliation timings in cotton containing a fruiting gap, Faircloth et al. (2004) found data that suggests that defoliating before 60% may help avoid discounts due to high micronaire while not sacrificing yields, given that the crop has no fruiting gap (Faircloth et al., 2004). Field experiments were conducted in 2004 and 2005 at Upper Coastal Research Station near Rocky Mount, North Carolina. The experiments were designed to investigate the effects of early, normal, and late defoliation timings, and early and late harvest timings, on a compact, normal, and extended fruiting habits. Treatments were arranged in a Latin square design with defoliation and harvest timings stripped across fruiting habits. In one study, PGRs were used in accordance to the Modified Early Bloom method, the Early Bloom method, and a Non-treated method which simulated the compact, normal, and extended fruiting habits respectively. The Modified Early Bloom method was accomplished by an application of 8 oz/A Mepiquat Chloride at match-head square, followed by another application of 8 oz/A Mepiquat Chloride at Early Bloom (5-6 white blooms per 25 feet of row). In another study, DP 444, DP 451, and DP 555 were planted to simulate the compact, normal, and extended fruiting habits respectively. Defoliation timings were 50% OB, 70% OB, and 90% OB. Harvest timings were 14 days after defoliation (H1) and 28 days after defoliation (H2). Data were analyzed and means separated using the General Linear Model in SAS version 9.1.3. Results, from the PGR study, indicate that defoliation before 60% OB is plausible, especially when fruiting is compact, without sacrificing yield or quality. Results also indicate that a delayed harvest can increase yield and reduce micronaire if weathering is minimal, however an early harvest can increase length, uniformity, and strength, especially at early defoliation timings. Results, from the variety study, indicate that delaying defoliation past the optimal, can increase yields, however an early defoliation timing can reduce micronaire. Also, delayed harvest can increase yield and strength, and reduce micronaire if weathering is minimal. [ABSTRACT FROM AUTHOR] |
