Corn tolerance and weed control with amicarbazone and metribuzin applied preemergence

Since the late 1950s, atrazine has been a cornerstone of corn ( Zea mays L.) weed control, but decades of use have raised concerns about groundwater contamination and enhanced biodegradation. Therefore, amicarbazone and metribuzin were evaluated as alternatives to preemergence use of atrazine in corn. Tolerance trials evaluated three rates of amicarbazone (490–980 g ai ha −1 ), metribuzin (280–560 g ai ha −1 ), and combinations of the two herbicides. Amicarbazone alone caused ≤12% injury. Injury was similar at lower combination rates but increased to 22% at the highest rate by 5 weeks after planting. Grain yield was reduced only when amicarbazone was applied at 980 g ai ha −1 at one location. A separate study evaluated hybrid sensitivity to amicarbazone + metribuzin; no differences in corn injury, height, canopy coverage, density, or yield occurred under the conditions of this study. Application timing of an amicarbazone + metribuzin premixture was examined. The least injury to corn occurred in plots receiving 14‐ and 7‐day preplant applications, whereas applications applied preemergence and 3 days after planting caused increasing levels of injury. Despite injury, no yield reductions were detected across application timings under the conditions evaluated. Weed control trials indicated that amicarbazone + metribuzin provided comparable control of Palmer amaranth ( Amaranthus palmeri S. Watson) and ivyleaf morningglory ( Ipomoea hederacea Jacq.) and greater control of several broadleaf and grass species compared to atrazine. With no yield reductions and weed control equal to or greater than atrazine, amicarbazone plus metribuzin shows potential as a preemergence alternative in corn.