Early defoliation effects on corn plant stands and grain yield

Multiple stresses can cause early defoliation in corn ( Zea mays L.). Corn response to hail damage depends on defoliation timing and severity. Our objective was to evaluate the effect of defoliating plants at 2.5‐cm above the soil beginning at V3 and continuing for three weeks in a three‐year study. Treatments were imposed with a string trimmer once or twice a week in a full factorial arrangement with timing of V3, V4/V5 and V6. At maturity, ears and plants were counted and harvested from 3 m at the center rows in each plot and weighed. A subsample was then shelled, and test weight, moisture, plants, ears and yield per hectare were determined. Defoliating twice a week between V3 and V6 reduced stands, ears and yield between 24% and 41%, compared with one defoliation a week. Defoliation at V6 decreased yield up to 100%, regardless of the occurrence of previous defoliation. Defoliation at V3, V4/V5 or both (without a defoliation at V6), especially twice a week, began to have an additive detrimental effect, but maximum plant, ear and grain yield losses (ranging between 33 and 77%) were smaller and less consistent compared to V6 defoliation. Here, the additive effect of frequency of defoliation at a given stage was reported for the first time. In this study, using a string trimmer to impose defoliation proved an effective and realistic method to simulate a wide array of biotic and abiotic defoliation damages to corn foliage.