Effects of Intensity and Frequency of Early Season Defoliation on Corn Grain Yield.

Multiple biotic and abiotic events can results in early season defoliation of corn plants. The recover from, and resulting impact of this defoliation depends on the timing, severity, and frequency. Our objective was to evaluate the effect of clipping plants at approximately 2.5 cm above the soil beginning at V3 and continuing for three weeks. Treatments were imposed with a string trimmer at one, two, or three times weekly in a full factorial arrangement with timing of V3, one and two weeks later, with four replications in a randomized complete block design. Plot size was 4, 76 cm rows by 7.6 m long. At maturity, all ears were counted and harvested from 3 m of row from the center two rows in each plot and weighed. A representative six-ear subsample was then shelled and grain test weight and moisture determined. Ears ha^-1, kernels ear^-1, kernel weight and cob weight were likewise determined on shelled samples. Defoliation during the first week (V3) even on multiple days had little effect on grain yield. By the second week, multiple defoliation timings decreased yield more than a single event. Defoliation during week the (V5-6) resulted in the greatest yield loss.