Pigeonpea weed management – testing herbicide crop safety and agronomic approaches to maximise crop competition

Abstract

For pigeonpea, weeds are a major constraint, worsened by the poor early competitiveness of the crop. To establish pigeonpea as a viable grain crop in Queensland, effective crop safe, pre- and postemergence herbicides will be critical. In addition, maximising the competitiveness of pigeonpea crops could help reduce crop losses and minimise the impact of weeds.
There are currently limited registered herbicides for pigeonpea grain crops. Previous seedling pot screening identified several promising herbicides which are now being tested in field trials. Trials were conducted at the Department of Agriculture and Fisheries (DAF) Wellcamp research farm comparing the crop safety of post-emergent (2023 and 2024) and pre-emergent (2024) herbicides with untreated controls. Several tested herbicides showed good crop safety, with minimal visual symptoms of crop damage, reduced growth, or yield. More trial work is required to confirm the crop safety of these encouraging herbicides, and to allow registration for use in pigeonpea grain crops.
With limited options for in-crop weed control and increasing concerns about herbicide resistance, agronomic practices with the potential to supress weed growth and seed production have potential to complement herbicide use. This study tested the effect of pigeonpea row spacing and plant density on “mimic” weed growth and seed production. The highest pigeonpea yields were achieved with the high population and narrow rows (45 plants/m² and 250 mm). The mimic weeds (Rhodes grass and millet) significantly reduced the yields of pigeonpea. Importantly, the pigeonpea crop also significantly reduced yield and dry weight of mimic weeds. The effect of narrow row spacing was larger than the effect of increasing crop density. Light interception of pigeonpea was significantly higher with narrow row spacing, suggesting narrow rows may be useful for increasing crop competition and weed control.