Western Australia
November 6, 2007
Like playing chess, outwitting
annual ryegrass, a major weed in Western Australia which can
develop resistance to more than one herbicide at a time,
requires constant vigilance and a strategic approach.
Farmers now have a greater understanding of the value of pasture
phases for controlling herbicide-resistant annual ryegrass in
low to medium rainfall areas, thanks to Graeme Doole from the
School of Agricultural and Resource Economics,
Institute of Agriculture, at
the University of Western Australia (UWA).
Dr Doole recently completed a doctoral study on the value of
different types of sown pasture for herbicide resistance and
recharge management in the WA wheatbelt.
Supervised by Professor David Pannell of UWA and Dr Clinton
Revell of the Department of Agriculture and Food WA, the
research was funded by the Cooperative Research Centre (CRC) for
Australian Weed Management and the Future Farm Industries CRC.
A variety of mathematical modelling techniques were used to
identify profitable solutions for managing annual ryegrass.
Exploiting recent advances in computer science, these techniques
allowed a substantial increase in the quality of recommendations
arising from existing models used in WA agriculture.
According to Dr Doole, the value of pasture phases is sometimes
overlooked, given the high relative value of cereal crops. His
research indicates that under certain conditions their strategic
inclusion is more profitable than maintaining a crop-only
system.
The value of French Serradella, a legume used as a break pasture
for nearly a decade in different land-use sequences, is
difficult to assess given the range of factors affecting its
profitability.
“Incorporating a single year of Serradella in a rotation is the
most valuable option at high weed densities, or where Group A
herbicides are ineffective against annual ryegrass.
“A three year phase is required if resistance to multiple
herbicide groups is observed,” he said.
In addition, cropping sequences incorporating lucerne can also
outperform continuous cropping, but only if one of the following
occurs:
1. annual ryegrass is resistant to all selective herbicides;
2. a water table is shallow so that dryland salinity is likely
to occur; or
3. prices for sheep products are high.
“The value of perennial pasture such as lucerne is then
sufficient to overcome its high establishment cost,” Dr Doole
said.
He concluded that sowing annual pastures was an attractive
option where grain production was threatened by ongoing
herbicide resistance problems.
“The multiple benefits of such pastures for a mixed farming
system are that legumes fix nitrogen, which benefits a
subsequent cropping phase, they can be integrated with highly
effective weed management options and they are also a valuable
feed source for sheep.
“However, it‘s important that sown pastures are carefully
managed if a farming system is to fully benefit from these
features,” Dr Doole said. |
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