Lint Yield, Earliness and Pink Bollworm Resistance of Cottons Treated with Ethephon and Untreated

An early -maturing, nectariless, okra -leaf germplasm line of cotton, Gossypium hirsutum L., designated WC -12NL, was compared with a fullseason, nectaried, regular -leaf cultivar, 'Deltapine 61' (DPL -61) over two locations, Maricopa, Arizona (AZ) and Brawley, California (CA), and two seasons, 1986 and 1987. Half of each plot was treated with ethephon ( =Prep) when the crop was approximately 60% open. Lint yields were higher in WC -12NL than in DPL -61 at AZ, but not at CA. WC -12NL was earlier maturing than DPL -61, but the difference was greater in untreated than in ethephon -treated plots and at AZ than at CA. From 33 to 67% less insecticide was needed to control pink bollworm, Pectinophora gossypiella (Saunders), on WC -12NL than on DPL -61. Pink bollworm infestations were also significantly lower in bolls of WC -12NL. INTRODUCTION Earliness of the cotton crop may be increased and insect populations decreased through the use of early maturing, insect -resistant cultivars and certain growthregulating chemicals. The objective of the study reported here were to compare 1) lint yield, earliness, and resistance to pink bollworm of an early maturing, nectariless, okra -leaf germplasm line with those of a fullseason, nectaried, regular -leaf cultivar; 2) yield and earliness in untreated plots and in those treated with ethephon. MATERIALS AND METHODS Plots of WC -12NL and DPL -61 were planted at the Imperial Valley Conservation and Research Center, Brawley, CA, on 31 March 1986 and 31 March 1987, and at the University of Arizona Maricopa Agricultural Center, Maricopa, AZ, on 24 April 1986 and 7 April 1987. Plots were arranged in five randomized complete blocks. Plot size was 48 rows X 189 m (540 ft) [ =0.81 ha =2.0 acres]. Rows were spaced 1 m (=40 in) apart. Short-season production systems were used at both locations. Irrigation was terminated 15 Aug 1986 and 14 Aug 1987 at AZ, and 30 July both years at CA. Ethephon was applied to half of each plot, at the rate of 1.12 kg/ha ( =1.0 lb /acre), on 24 Aug both years at AZ, and on 11 Aug 1986 and 17 Aug 1987 at CA. Defoliants were applied 20 Sept 1986 and 16 Sept 1987 at AZ, and 5 Sept 1986 and 31 Aug 1987 at CA. All other cultural practices were standard, except that plots in AZ were irrigated once each week instead of every 2 weeks to preclude water stress. The soil type at CA allowed us to irrigate every 2 weeks without causing stress. No early -season insecticide was applied because we wanted to measure the differential response of the cottons to thrips and lygus. For pink bollworm control, 50 green bolls per plot were harvested twice weekly and examined for eggs. Insecticide was applied separately to the two cottons when the action thresholds were reached (8% of the bolls with eggs at CA and 17% at AZ). Table 1 lists the number of insecticide treatments applied. Boll samples were also incubated to determine pink bollworm infestations in bolls.