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Early Defoliation Affects Corn Grain Yields¹

Field experiments designed to simulate hail damage at various developmental stages revealed an unexpected and potentially important grain yield response from corn (Zea mays L.). Of particular interest were yields following defoliation at the 5-leaf stage. Two hybrids representing different maturity classes were defoliated. One hybrid was full-season for southern Minnesota. The other was approximately 80%, of full-season. Yields of the full-season hybrid were decreased by 80% (3-year average, 1973 to 1975). Average yields of the short-season hybrid were increased by 48% (same 3-year period). Eleven additional early hybrids at one Southern Minnesota location were defoliated at the 5-leaf stage in 1975. Yield responses ranged from a 37%, increase to a 14% decrease. Trials conducted in 1976, involving several locations and hybrids, resulted in yield changes varying from a 32% reduction to a 53% increase — suggesting interactions among genotype, environment, and defoliation timing. We propose a physiological explanation for observed yield responses. It appears that early growth alteration or inhibition of leaf function could result in yield enhancement. Effective growth regulation might consist of altering source-sink relations at the time of reproductive initiation.

Key Words: Zea mays L. • Growth regulation • Flower initiation

² Authorized for publication as Paper No. 9918 in the Journal Series of the Minnesota Agric. Exp. Stn.

Received for publication August 12, 1977.

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