Chemical and Non-Chemical Weed Control in Wide Row Lupins and Chickpeas in Western Australia

Abstract

Organic crops are on the increase worldwide and weed control is one of the main problems since chemicals cannot be used. Wide row lupin sowing systems (greater than 50 cm wide rows) are becoming common in Western Australia (WA) and this allows growers to control inter–row weeds by inter-row cultivation for organic crops or spraying non-selective herbicides using shielded sprayers. In this study, inter-row shielded spraying was found to be the most effective treatment for annual ryegrass control in the 66 cm wide rows, but future herbicide resistance will be a major limitation. With shielded spraying, some form of intra-row weed control will still be necessary to significantly reduce weed seed set. Automatic tractor steering control would also be essential for commercial growers to adopt shielded spraying. In 2006, inter-row cultivation reduced annual ryegrass biomass by 63% and the number of annual ryegrass heads by 43%, but this did not result in a significant increase in lupin yield. To be most effective, it is suggested that inter-row cultivation should be done relatively early while the weeds are small, and when the soil is relatively warm and dry with rain not predicted for a day or two. In 2006 and 2007, inter-row shielded spraying with glyphosate gave the best ryegrass control averaging 94%. Weed seed head trimming or cutting weeds above the crop prior to weed seed maturity may be a useful non-chemical method to reduce the number of weed seeds set if the weed seed is above the crop canopy and the cutting height is well controlled. Indian hedge mustard (Sisymbrium orientale) seed collected in the 2005 chickpea harvest samples was reduced by around 35% with all trimming treatments. In 2006, the late flower trimming reduced the seed number of wild oats and volunteer wheat in chickpeas. Lupin and chickpea grain yield was slightly reduced by trimming in 2005, but with improved height control did not reduce yields in 2006. Given the difficulties in controlling weeds by the growers due to widespread development of herbicide resistance in these weeds within the WA wheatbelt, this novel non-chemical way of weed control is a viable promising option to reduce the soil weed seed bank.