Corn yield components and yield responses to defoliation at different row widths

Corn (Zea mays L.) defoliation experiments have been conducted for more than 130 yr in the United States. However, there are limited data on the effect of row width on defoliation in modern hybrids. A 2-yr experiment was conducted in Lexington, KY, with two hybrids (113 relative maturity [RM] and 120 RM), two row widths (38 and 76 cm) and a combination of defoliation timings and severities: 0% defoliation (control), V7 growth stage, and 100% defoliation (V7–100%), V14–50%, V14–100%, R2–50%, and R2–100%. No yield difference among hybrids was observed in 2012. Yields were 26% greater in 38-cm rows than 76-cm rows in 2012. For 2013, corn yield for 38 cm was 10% greater, but hybrid, row width, and defoliation interacted. Lowest yields were caused by V14–100% followed by R2–100% defoliations. Defoliations of V14–50% and R2–50% reduced yields in some cases. Complete defoliations at V7 did not reduce yields in most comparisons. Kernel number and kernel weight were most reduced by V14–100% and R2–100% defoliations, respectively. There is a potential for corn in 38-cm narrow rows to reduce grain yield losses after a defoliation event, when compared with corn in 76-cm standard rows.