Early-season floral bud loss has little impact on the maturity, yield, and lint quality of high-yielding Bt cotton crops

Abstract

Protecting floral buds (squares) from insect damage in cotton during early growth is a priority for crop managers despite unclear implications for yield potential and increased system risks from early-season insecticide use. This study was conducted to determine the compensatory responses of high-yielding Bacillus thuringiensis (Bt) cotton, Gossypium hirsutum L. cultivars, following manual square damage across 30 experiments, spanning different seasons and environments under commercial production conditions. Square removal from the first five sympodia (fruiting branches) before flowering reduced yield by 9% in one experiment, increased yield by 9%–12% in three experiments and had no effect in the remaining experiments. The most damaging treatment, with squares removed twice across 10 sympodia, reduced yield in just nine experiments by 10%–23%. Lint strength and length remained high, exceeding Australian market preferences. Micronaire decreased with later or more severe square loss particularly in shorter season environments, but economic impact varied. Compensatory growth following pre-flowering square loss increased fruiting site production without raising total biomass or boll proportion commensurately and caused only minor boll opening delay (<4 days). Yield compensation occurred through increased boll retention at the first position on upper canopy sympodia and more distal positions on remaining sympodia and was un-reliant on growth of additional mainstem sympodia. Square loss impacts were greater after commencement of flowering or when pre-flowering losses continued during the early-flowering period. Crop managers can have confidence to reduce pre-flowering pesticide use without jeopardizing high yields, which may produce additional systems benefits.