Timing Defoliation Applications for Maximum Yields and Optimum Quality in Cotton Containing a Fruiting Gap

Abstract

Stresses during cotton (Gossypium hirsutum L.) square and boll formation can result in fruit abscission from several continuous nodes, resulting in a fruiting gap on the plant. This gap may cause a shift in benchmarks for timing various agronomic practices aimed at maximizing cotton yield and optimizing quality. A cotton defoliation timing study was performed in 1999, 2000, and 2001 to (i) see if the creation of a fruiting gap would influence defoliation timing and to (ii) compare the use of the open boll percentage at defoliation (OBPD), nodes above cracked boll (NACB), and micronaire readings at defoliation as tools for timing defoliation. In late July or early August each year, a fruiting gap was created by physically removing fruit from several continuous nodes on plants. Plots were defoliated on the basis of various OBPD values. Upon defoliation, OBPD and NACB were taken and lint was retained to determine the micronaire at defoliation. In both 1999 and 2000, there was a yield advantage to delaying defoliation beyond 60 OBPD in treatments containing a gap. However, in 2001 there was no yield advantage to delaying defoliation. This may have been due to optimal late-season growing conditions experienced in 2001. In years when micronaire readings are high, data suggested cotton not containing a fruiting gap is more likely to be above discount levels for high micronaire and should not be defoliated past 60 OBPD. In both 1999 and 2000, trends confirmed a direct relationship between OBPD and both yield and micronaire. Overall, these studies demonstrated that in some years, where no fruiting gaps exist, it might be possible to terminate cotton before the 60% open boll recommendation without sacrificing yields. These results would allow farmers to shift defoliation, and hence harvest, to a time when there are fewer risks of quality-based discounts. While a significant interaction prohibited the examination of the use of micronaire at defoliation as a technique for timing defoliation, there did not appear to be a significant advantage to using either NACB or OBPD for timing defoliation.