Summer fallow is an important phase to target the control of problematic summer grass weeds. The summer grasses, awnless barnyard grass, feathertop Rhodes (FTR) grass and windmill grass, are major problem weeds in many Northern Region fallows. These weeds flourish in zero tillage systems, are prolific seed producers, and are not consistently well-controlled with glyphosate. As well, many populations of awnless barnyard grass and several populations of windmill grass have developed resistance to glyphosate.
Thus, improved management practices are needed for effective and sustainable control of these weeds. Best weed management practices, not only focus on controlling emerged seedlings, but take into account the seeds in the seed-bank, replenishment of the seed-bank and new incursions, with the objective to not only reduce weed numbers but to reduce the size of weed seed bank in the soil.
This paper summaries recent research on chemical control of these weeds in the Northern Region. Data from experiments will be presented on options to deplete the seed-bank with pre-emergent herbicides, control seedlings with glyphosate alternatives, control survivors with the double-knock tactic, and options for stopping seed-set on glyphosate sprayed survivors.
The parameters required for maximum efficacy of herbicide treatments will be discussed including the importance of targeting young weeds, the interaction of weed stress and the optimum interval between sequential herbicide applications when using the double knock.