Cover crops are not affected by tobacco soil residual herbicides but also do not provide consistent weed management benefits

Abstract

AbstractWinter cover crops (CCs) provide soil conservation benefits for strip-tillage tobacco producers, but soil-residual herbicides may interfere with their establishment and growth. Tobacco is planted later than many agronomic crops, but growers often terminate CCs early to minimize CC residue at planting, and this may reduce weed suppression potential. We examined residual herbicide effects on CCs across two seasons and the potential for CC-based weed suppression within strip-tilled tobacco. Mixtures of wheat plus crimson clover and cereal rye plus crimson clover were examined, with a no-CC control. Herbicides included two rates of PRE sulfentrazone (177 or 354 g ai ha–1) plus carfentrazone (20 or 40 g ai ha–1); the higher rate was also followed by POST clomazone (840 g ai ha–1) or mixed with PRE pendimethalin (1,400 g ai ha–1). Controls with no weed management and hand weeding were also included. CC density and biomass were not reduced by weed management (WM) treatments with residual herbicides. However, CCs did not reduce density of annual grasses, small-seeded broadleaves, or perennials in the tilled in-row or untilled between-row zones. Cereal rye plus crimson clover resulted in lower weed biomass at tobacco harvest in the untilled between-row zone in 2017. WM effects were variable between the years, weed groups, and zones. Adding clomazone or pendimethalin was more consistent for reducing weed density and biomass compared to the low rate of sulfentrazone plus carfentrazone. Tobacco yield was unaffected by CCs in 2017 but lower in some WM treatments in 2018. In this study, tobacco herbicides did not interfere with wheat, cereal rye, or crimson clover establishment, but additional research should determine if these results apply to other environments and soil types. However, when these CC species were terminated 5 to 6 wk before transplanting, they did not consistently contribute to weed control.