|
The heavy rains in parts of the northern grain region should sharpen the focus of growers on the early control of summer weeds', says Dr Steve Walker of the Weeds CRC and Qld Department of Primary Industries and Fisheries.
In particular, says Dr Walker, the key to getting on top of barnyard and liverseed grasses is to attack all parts of the weed lifecycle and keep the pressure on weed seedbanks.
New research confirming the value of this approach is particularly timely given awnless barnyard grass (Echinochloa colona) was earlier this year confirmed as Australia's second glyphosate-resistant weed.
And, while liverseed grass (Urochloa panicoides) has not yet developed glyphosate (Group M) resistance, it is at high risk, particularly for growers practising minimum or zero tillage.
According to Dr Walker, adopting an integrated weed management strategy that includes non-chemical tactics for controlling seedlings, and diligently stopping replenishment of the seedbank, will result in substantially fewer problems in the future.
'Barnyard grasses (Echinochloa spp.) and liverseed grass are the most common summer grass weeds of cropping in southern Queensland and northern New South Wales,' said Dr Walker.
'When uncontrolled, these weeds can reduce sorghum yields by 25-40 per cent.'
'An integrated weed management strategy that combines chemical and non-chemical tactics to stop seed production and seed rain, prevent the introduction of new seeds, deplete the weed seedbank and control seedlings will significantly reduce the impact of these weeds.'
Barnyard and liverseed grasses are favoured by reduced tillage systems, and have increased in number in the last two decades.
They are prolific seeders, are not consistently controlled with commonly used herbicides, and can be highly competitive.
Several populations of liverseed grass in southern Queensland, and one population of barnyard grass in northern NSW, have been confirmed as resistant to atrazine (Group C herbicide).
A population of awnless barnyard grass in northern NSW was recently confirmed as having developed glyphosate resistance, making it Australia's second glyphosate-resistant weed after annual ryegrass (Lolium rigidum).
The research follows the findings announced earlier this year by the Northern Herbicide Resistance Project (members of Weeds CRC, NSW Department of Primary Industries and Queensland Department of Primary Industries and Fisheries), that wild oats (Avena spp.), sowthistle (Sonchus oleraceus), flaxleaf fleabane (Conyza bonariensis), liverseed grass and barnyard grasses are all at risk of developing glyphosate resistance.
Three common factors determined the high risk category for these weeds. They all produce large quantities of seed, have a history of herbicide resistance somewhere in the world, and all occur in minimum tillage or no-till farming systems where they are exposed to multiple applications of glyphosate.
|
