Chemical Efficacy of Early Square Removal and Subsequent Productivity of Superokra-Leaf Cotton

Delaying fruit set of superokra-leaf cotton (Gossypium hirsutum L.) can potentially improve yields and provide an excellent trap-crop system for boll weevil (Anthonomus grandis Boh.) management if a practical means of early-season square removal could be obtained. We determined the efficacy of ethephon (2-chloroethylphosphonic acid) applications on removing early squares, effectiveness of Ag⁺ at reducing damaging effects of ethephon on plant terminals, and subsequent effects of these treatments on the reproductive development of field-grown superokra-leaf cottons. All square-removal treatments caused a significantly greater number of early squares to abscise than occurred normally in untreated plots, but ethephon treatment results were variable. Side-directed applications of 8 or 12 mM ethephon at 0.28 kg ha⁻¹ and 20 mM ethephon at 0.68 kg ha⁻¹ removed an average of 124% more squares than manual square removal in 1986. In 1987 and 1988, however, 0.28 kg ha⁻¹ ethephon removed 16 and 24% fewer squares than manual methods, respectively. A 200-mg L⁻¹ AgNO₃ pretreatment on plant terminals significantly reduced the number of squares abscised in the ethephon treatments by 20 and 36% in 1986 and 1988, respectively, and did not consistently improve yield or earliness. Removal of early squares delayed the initiation of fruiting, which continued into a delayed crop maturity. Fruiting occurred more rapidly in square-removal treatments than controls, but the fruiting period still extended later into the growing season, regardless of the accelerated rate. The effect of square removal on seedcotton yield was variable. Square-removal treatments averaged 2261, 1914, and 2652 kg ha⁻¹ of seedcotton in 1986, 1987, and 1988, respectively. Controls averaged 2585, 1546, and 2839 kg ha⁻¹ in the same respective years. A difference in environmental conditions during fruiting was considered an important factor in yield differences. Although side-directed applications of ethephon were effective in removing early squares, the variability in yield and the delay in crop maturity offset any potential advantages it may have in a boll weevil trap-crop system. Approved for publication by the director of the Louisiana Agric. Exp. Stn. as manuscript no. 89-09-3013.