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Defoliation Effects on Corn Hybrids Adapted to the Northern Corn Belt¹

Hail damage to corn (Zea mays L.) in the northern corn belt is assessed using loss charts based upon research conducted in the central corn belt. We conducted an experiment to determine the effect of leaf blade defoliation at varying stages of development on corn grain yield, test weight, kernel weight, shelling percentage, and ear moisture content at harvest. Plants were completely defoliated (blade only) at the five-leaf stage (LS). Both 50 and 100% of leaf blades were removed at 13 LS, tasseling, early milk, and full dent growth stages. The 3-year study included two hybrids, a full-season [115 relative maturity (RM)] and a short-season (90 RM) hybrid.

Complete leaf removal of the 90-RM hybrid at the five LS caused an average 48% grain yield increase compared with no defoliation. The same treatment caused an average 7% yield reduction of the 115-RM hybrid. At later defoliation dates, grain yield reductions were greater for plants that were 100% defoliated than for plants that were 50% defoliated. The yield responses to defoliation at various stages of development for both 50 and 100% leaf blade removal were similar for the 90- and 115-RM hybrids. Although yield reductions were comparable when the two hybrids were 100% defoliated for all stages of development, 50% defoliation did not cause as great a yield reduction on the 90-RM hybrid as it did on the 115-RM hybrid. In general, observed grain yield losses from defoliation after the five LS were similar to those given in loss charts used by crop-hail insurance adjusters.

Kernel weight, test weight, and shelling percentage were not affected when plants were defoliated, either 90 or 100%, prior to tasseling. Leaf removal after tasseling, especially 100%, lowered kernel weight, test weight, and shelling percentage of both hybrids. We did not record kernel number per ear which must account for the yield increase resulting from five LS defoliation because kernel size and ear number per plot were not affected.

In general, ear moisture content at harvest was slightly increased due to defoliation imposed prior to tasseling and decreased due to defoliation after tasseling which indicates defoliation before tasseling slightly delayed maturity and defoliation after tasseling hastened maturity, as measured by ear moisture content at harvest.

Key Words: Zea mays L. • Maturity • Test Weight • Stage of development

² Professor, Dep. of Agronomy and Plant Genetics, St. Paul, MN 55108; professor, Dep. of Soil Science; and superintendent, Southwest Exp. Stn., Lamberton, MN 56152; and associate professor, Dep. of Agronomy and Plant Genetics and agonomist, Southwest Exp. Stn., Lamberton, MN 56152.

Received for publication April 24, 1976.

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