Influence of Clethodim Application Timing on Control of Volunteer Corn in Soybean

Abstract

Herbicide options for management of volunteer corn in soybean include a variety of acetyl CoA carboxylase-inhibiting herbicides, yet often, applications of acetyl CoA carboxylase herbicides are delayed until the weed is visible above the soybean canopy. Volunteer corn growing above the soybean canopy is a highly competitive weed, and herbicides applied at this point can kill the weed, yet soybean yield loss is still a concern. Our objective was to compare the effect of controlling various densities of volunteer corn growing in soybean EARLY (≤ 30 cm) versus LATE (≈ 90 cm) on percent control and soybean yield. Seven volunteer corn densities (0, 0.5, 2, 4, 8, 12, and 16 plants m−2) were hand planted into 19-cm row soybean. Clethodim 79 g ai ha−1was tank-mixed with glyphosate at 840 g ae ha−1and applied to the volunteer corn EARLY and LATE. The EARLY application provided higher and less variable control of volunteer corn 14 d after treatment (DAT) compared to LATE applications at all volunteer corn densities. There was no difference in control at 28 DAT for both the EARLY and LATE applications. Soybean yield was not affected by either application timing. Although no yield reduction was seen with the LATE treatments, later-season applications of clethodim to control volunteer corn may offer more variable control and could allow for additional Bt selection pressure on targeted insect pests.