Effects of simulated insect damage and weed interference on cotton growth and reproduction

Abstract

SummaryEarly‐season insect pests of cotton (Gossypium hirsutum L.) crops, including Lepidoptera larvae and mirids, feed on vegetative buds. The loss of vegetative buds transiently delays the plant's development and growth and has the potential to reduce its competitive ability. Yield reductions due to weed interference and insect damage, therefore, could be greater than expected from the additive effects of weeds and damage acting separately. Three varieties, two levels of weed infestation, and two levels of simulated damage were combined in a factorial experiment designed to assess the responses of cotton plants to the combined effects of damage and weeds. Weed treatments were: with (+W) and without weeds (‐W), and damage treatments included: undamaged control (‐D) and damaged plants (+D) which had their active vegetative buds removed at 30 and 49 days after sowing.Variety and interactions between variety and other factors were normally nonsignificant for all the response variables measured in this experiment. Cotton height, width, production of flowerbuds and production of fruit were all affected by both damage and weeds. While the effects of damage on these growth variables were transient, the effects of weeds normally increased with time throughout the season. Non‐additive effects of weeds and damage were minor for plant height and width, and large for flowerbud and fruit production.At maturity, weed dry matter ranged from about 20 g m‐2 (‐W treatments) to 300 gm‐2 (+W), cotton dry matter from 144 gm (+W+D) to 945 gm‐2 (‐W‐D), and seed cotton production from 54gm‐2 (+W+D) to 417 gnT‐2 (‐W+D). Damage did not affect vegetative dry matter and marginally increased seed production in ‐W plots. Non‐additive effects of weeds and damage were negligible for vegetative dry matter but highly significant for seed production (P < 0.0001). These contrasting responses of vegetative and reproductive growth are in agreement with neighbouring models of plant competitive interactions that emphasise the effects of neighbour interference on the fecundity of target plants that are not mediated by changes in target‐plant size.