Abstract
Boll weevil, Antoninus grandees Bohemian, and boll worm, Heliothis zea (Boddie), damage and yield were compared in conventional dry land, furrow-diked dryland and irrigated cotton, Gossypium hirsutum L., production systems from 1983 to 1986. Boll weevil damage to squares was statistically similar in conventional dryland and furrow-diked dryland cotton during the overwintered generation during July. However, damage to squares and bolls was significantly higher in furrow-diked cotton during the first weevil generation in August compared with conventional dryland cotton. A combined analysis of variance indicated that damage was highest in irrigated cotton in both generations from 1984 to 1986. Bollworm damage was significantly higher in irrigated cotton, but there were no significant differences between furrow-diked and conventional dryland cotton. Yields were statistically similar in conventional dry land and furrow-diked dryland cotton, but significantly higher yields were obtained in irrigated cotton. The lack of significant yield increases in furrow-diked cotton compared with conventional dry land cotton was probably the result of increased weevil damage in the diked cotton. Three subplots within each of the three water management treatments consisted of untreated cotton and two schedules of insecticide application. Two applications of azinphosmethyl at 281 g (AI)/ha were applied at or a few days after first one-third-grown square stage to suppress overwintered weevils. These early-season applications suppressed damage caused by overwintered weevils in three of four years, but they had less effect on damage caused by first-generation weevils. Bollworm damage was higher in sprayed plots in only one of the four years. Yield increases were not obtained in plots receiving early-season insecticide applications compared with untreated plots. Reasons for failure of insecticide applications to increase yield are discussed. Early-season insecticide applications for boll weevil control do not appear to offer an effective means to increase yield in conventional dry land, furrow-diked dryland, or irrigated cotton in the Texas Rolling Plains.
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