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Correlation of Defoliation Timing Methods to Optimize Cotton Yield, Quality, and Revenue  [2006]

Siebert, J.D. Stewart, A.M.

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The inconsistent nature of timing cotton defoliation indicates the need for ongoing research in an effort to develop a more concrete set of recommendations. Defoliation timing based on mature fruiting (sympodia) branches (MFB) and the correlation between three defoliation timing methods, heat unit (HU) accumulation after 5 nodes above white flower (NAWF5), open boll percentage at defoliation (OBPD), and nodes above cracked boll (NACB), were evaluated to determine which method was the most consistent for maximizing yield, fiber quality, and revenue. Harvest-aids were applied when a physiologically mature first position boll was present at 5, 7, 9, 11, or 13 main stem nodes (MFB) above the first sympodial branch with a harvestable boll. At those times, OBPD, NACB, and accumulated HU beyond NAWF5 were recorded. Heat unit accumulation was significantly correlated to total lint yield and was the best method of determining crop maturity; however, because of the practical limitations of using this method, OBPD, which was significantly correlated to lint yield in three of four studies and was highly correlated to HU accumulation in all studies (r = 0.935), was the preferred method rather than NACB. With a full season cultivar (DP 555 BG/RR), maximum lint yield was obtained by defoliating at 10 MFB (42 to 64 OBPD, NAWF5 + 790 to 906 HU, 4 to 5 NACB). Defoliating an early maturing cultivar (ST 4892 BR) at 8 MFB (17 to 40 OBPD, NAWF5 + 701 to 814 HU, 6 to 7 NACB) did
not significantly reduce yield. To maximize lint yield with early defoliation, a second harvest may be necessary. Delaying crop termination until after 75 OBPD had detrimental effects on fiber quality leading to quality-based discounts and reduced gross revenue.