Isoxaben is an inhibitor of the synthesis of cellulose from glucose. Some dicot weed species are relatively insensitive to isoxaben inhibition. This study investigates mechanisms by which decreased sensitivity may occur in three dicot weed species: catchweed bedstraw, redroot pigweed, and velvetleaf. Dose response curves were generated to determine I50 values for the inhibition of glucose incorporation into cellulose by isoxaben and compared to that of a sensitive species, mouse-ear cress. Metabolic detoxification and uptake rates were measured and the degree of tolerance conferred by these mechanisms was calculated. In all cases, metabolic detoxification was negligible. Lower uptake rates were significant but minor components of tolerance in all species. It is suggested that the principal cause of isoxaben tolerance in these dicot weed species is decreased sensitivity at the target site.

PRE herbicides have been reported to injure both the foliage and roots of hybrid bermudagrass turf established in sand culture. Research was conducted to evaluate the influence of reed-sedge peat moss (RSPM) on hybrid bermudagrass injury following PRE herbicide applications to plants established in sand culture. Washed sod plugs were established in mini-rhizotrons constructed with sand root-zones varying in organic carbon content (0.000, 0.003, 0.007, and 0.012 kg kg−1). Herbicide treatments included indaziflam (35 and 52.5 g ai ha−1) and prodiamine (840 g ai ha−1). Significant foliar injury was only observed with indaziflam at 52.5 g ha−1. When applied to plants in sand with no detectable (0.000 kg kg−1) organic carbon, foliar injury measured 61% by 6 wk after treatment. Comparatively, injury with indaziflam at 52.5 g ha−1 was reduced by 40% with applications to plants established in sand with 0.007 kg kg−1 organic carbon. Root length, root length density, and root surface area were greatest in sand-based root zones with ≥ 0.007 kg kg−1 organic carbon regardless of herbicide treatment; however, only indaziflam (52.5 g ha−1) and prodiamine-treated plants exhibited diminished root parameters relative to the nontreated check. Data in the current study illustrate that RSPM can affect above- and belowground injury following PRE herbicide applications to hybrid bermudagrass in sand root-zones.