[ASC-media] WHEAT A WEAPON IN WEED WAR : Crop Doctor
brendon at iinet.net.au
Wed Nov 9 13:29:07 EST 2005
WHEAT A WEAPON IN WEED WAR 9.11.05
Asking intensive croppers to take paddocks out of crop for up to four years
is a tough message to sell, but one that herbicide resistance specialist
Bill Roy says is absolutely vital if producers want to retain herbicides as
a weapon against annual ryegrass.
In some parts of WA, herbicide resistance is so bad it has wiped out the use
of four major chemical groups.
Mr Roy was one of the speakers at the Grains Research and Development
Corporation (GRDC) updates held around southern Australia recently, where he
reported on the results of an eight-year herbicide resistance project,
supported by growers and the Australian Government through the GRDC.
He recommended three key management principles to follow after herbicide
resistance develops: prevent seed return to the seed bank, reduce the seed
bank before sowing and maximise the competitive capacity of the crop.
Mr Roy said growers should not wait until their weeds had developed
resistance to more than one type of chemical before tackling the problem and
he warned there were no signs of new herbicide options on the horizon.
He emphasised that growers had to stop relying on "drum power" alone to
control weeds and start using non-chemical options such as brown or green
manuring, grazing stock on the weeds, a weed-free fallow, growing fodder
crops for early cutting, spray or crop topping and burning stubble.
Taking a paddock out of crop and using such options to achieve a weed break
was vital to reduce the seed bank to a manageable level and it was important
to understand the potential of a seed bank to influence crops in the
Mr Roy said this was very much a numbers game that was influenced by natural
decay such as predation by insects and by the percentage of seeds that
germinated the following year. He pointed out it was possible for ryegrass
seeds to remain viable in the soil for at least four years.
Demonstration trials conducted at three sites in WA showed that taking a
paddock out of crop for three years was much more effective than doing it
for one or even two years. At the site that had a one year break, no
ryegrass plants were detected in the crop the following year. But this
jumped to 88 plants per square metre by the third crop and 213 plants/m² by
the fourth crop.
At the site that had a two-year break, 28 plants/m² were found in the fourth
subsequent crop and 143 plants/m² the year after. In contrast, at the site,
which had three years out of crop, less than 10 ryegrass plants/m² were
detected in each of the five following crops.
Mr Roy said wheat was one of the most effective weapons in the battle
against annual ryegrass and growers needed to choose the most competitive
varieties, sow them at high seeding rates and provide optimum nutrition.
They also needed to rotate the use of herbicides with different modes of
He said the final success of a weed control program was not simply the
number of surviving weeds, but the number of dollars in the bank. At each of
the three sites, various management programs were compared by recording
ryegrass populations, yield data and the cost of inputs over the eight-year
life of the project.
The best outcome was achieved in a block where the eight year gross margin
was $2137 per hectare. This reflected the outstanding control achieved by
use of a number of options, particularly a three-year pasture break, use of
strong competitive wheat varieties at high seeding rates and judicious
burning of stubbles following high yields.
The Crop Doctor is GRDC Managing Director, Peter Reading, Tel 02 6272 5525
GRDC REF: CDNov052.doc
Brendon Cant & Associates
Public Relations & Marketing
114 Branksome Gardens
City Beach WA 6015
Tel 08 9385 7779
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