Corn Yield Response to Defoliation At Different Row Widths.

Corn (Zea mays, L.) hybrids exhibit different yield responses to defoliation timing and rates. There is limited data on the effect of row width on defoliation in modern hybrids. A two-year experiment was conducted in Lexington, Kentucky (38° 7'42.57"N, 84°29'27.91"W), in a Maury Silt Loam with 2 to 6% slopes. The objective of this experiment was to determine the effect of corn defoliation in 38- and 76-cm rows. Treatments for this experiment include: control (no defoliation) and defoliation events at growth stage V7 (100% rate), V14 (50 and 100% rates) and at R2-R3 (50 and 100% rates). Overall, 2012 corn yield in 38-cm rows width was greater than for corn in 76-cm rows. Defoliation at V7-100% resulted in the greatest numerical yield value which was not different than yield for the control. Defoliation within the critical period for yield determination (V14, a few days before anthesis, and R2, about 2 weeks after anthesis) greatly reduced the yield with V14 defoliation resulting in the greatest yield loss. For both defoliation timings, 100% defoliation caused greater yield loss than 50%. Kernel number was reduced most by V14 defoliation. Kernel weight was reduced most by R2 defoliation.