Comparative survey of weeds surviving in triazine-tolerant and conventional canola crops in south-eastern Australia

D. LemerleA, R.E. BlackshawB, A.B. SmithA, T.D. PotterC and S.J. MarcroftD


A NSW Agriculture and Cooperative Research Centre for Weed Management Systems, Agricultural Institute, PMB, Wagga Wagga, New South Wales 2650, Australia


B Agriculture and Agri-Food Canada, Box 3000, Lethbridge, AB T1J 4B1, Canada


C South Australian Research and Development Institute, PO Box 618, Naracoorte, South Australia 5271, Australia


D Department of Natural Resources, Victorian Institute of Dryland Agriculture, PMB 260, Horsham, Victoria 3401, Australia


Abstract

Many farmers grow triazine-tolerant (TT) canola to enable control of difficult weeds and to allow early sowing. The efficacy of triazine herbicides in canola influences the development of future weed problems. A survey was conducted to determine the incidence and abundance of weeds surviving in TT and conventional canola crops across south-eastern Australia. Fifty-five canola paddocks (27% TT and 73% conventional) were selected at random in August/September 1998 when most weed management practices were already completed by farmers. Seventy-three weed species were identified, some at densities of up to several hundred plants m-2.

This has serious implications for weed seedbank replenishment and the perpetuation of weed populations requiring control in future crops. The most widespread grass species at more than 30% of sites were Lolium rigidum, Avena spp., and Vulpia spp., while the main broadleaf weeds were Arctotheca calendula, Polygonum avicu-lare, and Fumaria spp. Some weeds were more prevalent in conventional canola (e.g. Fumaria spp., Arctotheca calendula, Capsella bursa-pastoris and Papaver somniferum) while others were more common in TT (e.g. Anagallis arvensis, Raphanus raphanistrum, Lepidium afri-canum and Conringia orientalis). These results suggest that widespread adoption of TT canola will affect weed population dynamics in canola thereby leading to new weed problems in canola.

 

Plant Protection Quarterly (2001) 16 (1) 37-40.