cotton - Greenmount Press

Herbicide options shrinking for
cotton
■ By Brogan Micallef and Stephen Powles, Australian Herbicide Resistance Initiative
AT A GLANCE…
■ Over-reliance on glyphosate and Roundup Ready crops has
led to a major glyphosate resistant weed problem in the US;
■ Australia is at risk of a similar situation, especially in cotton
regions with the almost universal uptake of RR cotton;
■ Cotton growing regions and the northern grain region are
closely aligned, increasing the resistance risk as glyphosate is
used in many situations; and,
■ To face the herbicide resistance challenge, diversity is key.
NSW, populations of three common grass weeds – awnless
barnyard grass, liverseed grass and annual ryegrass (also
occurring in southern NSW) – now have resistance to glyphosate.
Adding to this issue is the increasingly frequent observation of
weeds with resistance to multiple herbicides.
THE evolution of herbicide resistant weeds currently
threatens global crop productivity as grain and fibre
production is substantially underpinned by the use of
herbicides for weed control. In recent years, the high adoption of
RR crops and over-reliance on glyphosate in the US has led to the
evolution of glyphosate resistant weeds.
To consider the global herbicide resistance challenge, the
Grains Research and Development Corporation (GRDC) funded
Australian Herbicide Resistance Initiative (AHRI), based at the
University of Western Australia (UWA), will host an international
conference on herbicide resistance in crops and weeds. The
Global Herbicide Resistance Challenge conference will take place
in the portside city of Fremantle, Western Australia from February
18–22, 2013 (www.herbicideresistanceconference.com.au).
Glyphosate resistance: A world-wide issue
Due to over-reliance on glyphosate and Roundup Ready (RR)
crops, along with the subsequent emergence of glyphosate
resistant weeds, the US now has a major resistance problem.
Of the 90 million hectares of corn, soybean and cotton crops
in the US, nearly all grow RR varieties. In RR corn, glyphosate
is used alone for weed control in 85 per cent of cases; 94 per
cent in RR soybean crops, and 89 per cent in RR cotton. US
farmers, researchers and the agricultural industry are now
doing everything possible to manage the subsequent resistance
problem, including hand weeding, a practise not seen in Western
agriculture for 100 years. Currently, 52 per cent of cotton crops
in Arkansas are hand weeded at high cost.
Given the uptake of RR technology by the nation’s cotton
industry, there is a risk of a similar situation developing in
Australia. Typically, there are two to three applications of
glyphosate used for summer fallow, and two for winter fallow.
In RR cotton, two applications of glyphosate is the norm. The
good news is that herbicides can be kept working, but Australian
cotton growers must be encouraged to do all they can to avoid a
similar situation to the US. To ensure sustainable systems for the
future, we need to practise diversity.
The Australian story: Glyphosate resistance in
NSW and QLD
Herbicide resistant weed populations are increasingly common
in agricultural systems of NSW and Queensland. In northern
Jason Norsworthy inspecting a field with plenty of pigweed.
C O N F E R E N C E
Herbicide resistance
threatens global food
and fibre production
From 18-22 February 2013,
world resistance experts
will be in Perth to address
this serious issue.
This is a unique opportunity
to learn how to ensure long
term sustainability of grain
and fibre crops.
To register, go to:
www.herbicideresistanceconference.com.au
December 2012–January 2013 The Australian Cottongrower — 47