Using pre-emergent herbicides for the control of Sicklepod (Senna obtusifolia) in the wet tropics

Sicklepod (Senna obtusifolia) is a significant weed of many parts of Queensland, from Mackay to Cape York. It can invade pastures, crops, road and power line corridors, clearings and creek banks. Previous research identified a suite of pre-emergent herbicides that when applied pre-wet season proved to be successful in controlling the seed/seedling bank during the short “Wet” season in the Dry Tropics. This study tests whether these herbicides will also prove effective in wetter tropical areas infested with sicklepod. The herbicides are being tested in various landscapes of the Wet Tropics where sicklepod has become dominant such as riparian zones, steep hillsides, adjacent pasture and fallow agricultural areas. Additional impediments to weed control in the wet tropics include a shorter window of opportunity for herbicide application and longer wet periods with higher rainfall totals. However, the higher productivity of arable and grazing land in the wet tropics environment makes herbicide application for weed control a viable option. Using the same herbicides and rates as proven successful in the Dry Tropics, with the addition of Valor®, initial baseline data has been collected and treatments of both post and pre-emergent herbicides have been applied. Valor® was included as a post emergent treatment as it may be more suited to higher rainfall areas. The postemergent treatments were added to ensure the ground is clear of sicklepod prior to pre-emergent herbicide application. Early results indicate a significant reduction in seedling emergence. Further preemergent treatments will need to be applied to exhaust the existing seed bank.