Effect of Early Season Square Removal on Three Leaf Types of Cotton

In certain environments, reduced leaf-open canopy cottons (Gossypium hirsutum L.) allow more light penetration and air circulation within their canopies than do normal leaf types. However, too much reduction in canopy can reduce overall productivity and economic yield. Removal of floral buds (squares) early in the season has been shown to result in larger plant size. Square removal was carried out in the field (fine-silty, mixed, thermic, Aquic Fragiudalf soil type) on normal, okra, and super okra leaf type near-isogenic lines of a ‘Stoneville 213’ background cotton for 3 and 6 weeks to determine i) if improved yield could be obtained in one or both open canopy types by enlarging the canopy and ii) if delaying fruit set produced differential responses in these leaf types. Results would form a basis for development of a boll weevil (Anthonomus grandis Boh.) trap crop system using exogenous chemicals to effect square abscission. Removal of squares increased plant height, leaf area index (LAI) and number of sympodial branches. The super okra leaf type produced the greatest responses to square removal. Fruit set was more rapid and occurred during a shorter interval for all leaf types undergoing square removal for 3 weeks, but the greatest response was obtained from super okra. Comprehensive analysis in 1983 indicated the rapid fruit set was due primarily to more sympodia fruiting simultaneously. The 3-week treatment was more consistent in this response than the 6-week treatment because of the generally shorter horizontal and vertical flowering intervals. Economic yield of normal and okra leaf types was generally not improved by square removal, whereas the super okra leaf type in the 3-week square removal treatment produced an average 23.5% greater lint yield than its control. Differences in lint percentage were significant between treatments in 1981 with significant leaf type by treatment interactions in 1983. The data indicate that the super okra leaf type had the most consistent responses to 3 weeks of manual square removal. These results imply that this leaf type would produce the best response to exogenous chemical abscission of squares and the greatest chance of recovery from early season insect pressure.