Large crabgrass and Texas panicum control with Group 15 herbicides applied preemergence

Abstract Gramineous weeds have become increasingly problematic in field crops over the past decade, especially in crops without herbicide tolerance traits, making effective management of them more challenging. The objective of this study was to compare the efficacy of four very-long-chain fatty acid (VLCFA) elongase–inhibiting herbicides for preemergence control of two grass species, large crabgrass and Texas panicum, which produce seeds of different sizes. The results were consistent across locations and rating times. Applications of all evaluated herbicides resulted in >94% visible control of crabgrass, while control of Texas panicum ranged from just 50% to 87%. The greatest level of Texas panicum control occurred after applications of pyroxasulfone + carfentrazone, whereas all treatments demonstrated similar efficacy against large crabgrass compared with plants that served as nontreated controls. Visible weed control ratings aligned with normalized difference vegetation index readings collected from both unmanned aerial vehicles and a handheld GreenSeeker device, as well as with biomass measurements. Furthermore, stand counts of both weed species exhibited no significant differences among the herbicides. These findings indicate that the selectivity of herbicides that inhibit VLCFA elongase on grass species when applied preemergence may be attributable to differences in seed size.