Late season beet armyworm (Lepidoptera : Noctuidae) infestations on cotton: Defoliation, fruit damage, and yield loss

Field cage studies were conducted in 1996 and 1997 to measure the effects o f late season beet armyworm, Spodoptera exigua (Hubner), infestations (0, 1 , 3, and 6 egg masses per 5.1 m row) on defoliation, fruit damage, and yiel d of cotton. Significantly higher light penetration through the cotton cano py was observed in most infested plots compared with non-infested control p lots. A trend for higher numbers of damaged fruiting forms (squares and bel ls) with increases in egg mass density was observed. There were no signific ant differences in the number of damaged fruiting forms among treatments, h owever, plots infested with 1, 3, or 6 egg masses had 2.3, 2.4, and 3.3-fol d more damaged fruiting forms than the control plots. In all infested plots , a significantly higher percentage of shed fruiting forms were damaged com pared with the control plots in 1996. In 1997, only plots infested with 6 e gg masses had a significantly higher percent of the cumulative fruiting for ms damaged compared with the control plots. In both years, there were no si gnificant differences in seed cotton yield among treatments.