Jennifer Barker jennifer.barker at adelaide.edu.au
Mon Jan 14 00:18:40 CET 2008

**For northern NSW and southern Qld agricultural districts**

14 January 2008								

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%.' 

'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.

Integrated weed management strategies attacking all parts of the barnyard
and liverseed grass lifecycle are available from the Weeds CRC factsheet:

Further information about glyphosate resistance is available from the
Glyphosate Sustainability Working Group website

Dr Steve Walker, Weeds CRC/Qld Department of Primary Industries and
Fisheries, 0419 463 988

Images and further information
High resolution weed photos can be downloaded directly from
Contact Jenny Barker - 08 8303 7250 or jennifer.barker at adelaide.edu.au 

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