South Perth, Western Australia
February 15, 2007
Background
weed densities must be high to make delayed sowing a worthwhile
strategy for weed management in lupin crops according to latest
research by the Department
of Agriculture and Food,
Western Australia.
Department researcher Bob French (photo) said
ryegrass densities would need to be reduced by at least 50
plants/m2 or radish densities by at least 2 plants/m2 to
compensate for the reduced yield potential due to delayed
sowing.
Dr French said if background week burdens were
not at least this high, reduced competition would not compensate
for the loss of yield potential where maximising grain yield was
important.
The Department’s research, being presented today
at the Agribusiness Crop Updates, aimed to investigate whether
dry sowing was still appropriate given the development of
resistance in a small pool of available herbicides.
“Dry sowing lupins has been a widespread practice
in Western Australia, but it is a strategy that utterly depends
on in-crop herbicides for weed control,” Dr French said.
“Growers have been encouraged to plant lupins
into moist soil to improve the activity of pre-emergent
simazine, and also to delay sowing for up to a week following
the break to allow germinating weeds to be controlled by
non-selective methods.
Dr French said any improvement in weed control,
however, must be traded off against reduced yield potential, the
need to sow other crops, and the risk that the soil may be too
dry to sow into after the delay.
“Our research modeled the yield penalty for
delaying sowing after the break at Merredin, Buntine and
Mingenew, and compared it to yield losses expected from
competition with wild radish and annual ryegrass,” he said.
“We found improved wild radish control could
often compensate for the yield penalty for delayed sowing, but
it was less likely that this would be achieved with improved
ryegrass control.”
He said the other risks from delayed sowing
included the risk that seedbed conditions would not be suitable
a week after the break.
Modelling revealed that at Mingenew there was a
50 per cent chance that a second sowing opportunity would not
occur until more than two weeks after the break, and at Buntine
until more than three weeks after the break.
Dr French said producers needed to consider other
benefits of delayed sowing to improve weed control such as
savings in selective herbicide costs and reduced weed seed
production leading to lower weed burdens in following crops.
“These would need to be considered in a rigorous
analysis of the value of delayed sowing as a weed management
tool,” Dr French said.
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