Heavy reliance on herbicides for goosegrass (Eleusine indica Gaertn.) control has led to the development of paraquat,
glufosinate, fluazifop and/or glyphosate resistance in goosegrass. This study aimed to evaluate the efficacy of preemergence
herbicide, S-metolachlor-treated oil palm frond powder on inhibition of resistant biotypes of goosegrass
under glasshouse and field conditions. The oil palm frond (OPF) powder was treated with S-metolachlor at its suboptimal
rate and applied as mulch. The herbicide-resistant goosegrass plants were found to be more inhibited when treated
with S-metolachlor-treated OPF mulch at the rate of 12 g ai ha–1 S-metolachlor + 1.5 t ha–1 OPF (with the exception of
the glufosinate-resistant googegrass biotype in the sandy loam soil) compared to the growth of the resistant biotypes
in silty loam soil under glasshouse conditions. Field experiments in an ambarella (Spondias dulcis L.) farm further
showed that OPF -treated with S-metolachlor mulch at the rate of 32.0 g ai ha–1 S-metolachlor + 4.0 t ha–1 OPF provided
great suppression of glyphosate-resistant biotypes of goosegrass with more than 85% reduction of weed density and
biomass, respectively. These results suggested that the residue of OPF have the potential to reduce the application rate
of S-metolachor without compromising on the excellent control obtained in combating these herbicide-resistant biotypes
of goosegrass.