[Photo: Brookton wheat at Beverley in 2004: The right plot was treated with inversion by a mouldboard plough and the left was untreated. Photo - Susan Hall]
Burn them, bury them or have them eaten - three options for graingrowers in dealing with troublesome weed seeds.
Incineration by burning windrows, inversion with a mouldboard plow to a depth where seeds cannot emerge from the soil, and ingestion by ants can all be used to tackle weed seeds. Each has advantages and disadvantages, allowing growers to decide what is best for their particular farming system.
Incineration is widely practised, although weed seed removal is only effective when the burning conditions are right, according to researcher Dr Michael Walsh of the GRDC-supported WA Herbicide Resistance Initiative.
"Burning temperatures and durations of 400°C for 10 seconds are required to kill annual ryegrass seeds and 500°C for 10 seconds for wild radish, meaning burning narrow windrows will be more effective than burning stubble because of the
concentration of fuel in the windrows," he
says. "Obviously, seed not collected in the
windrow due to shattering before harvest
will not be targeted by windrow burning.
"This tactic is variable and depends
on seasonal conditions, but provides
between 80 and 90 percent control of
weed seeds present in the windrow."
Another researcher, Dr Sally Peltzer
from the WA Department of Agriculture,
says inversion, or burial, can be an
extremely effective method of weed
seed removal on suitable soil types.
Trials show a one-off soil inversion
using a mouldboard plough can reduce
ryegrass numbers by more than 95
percent if full inversion at greater than
10 centimetres is achieved, resulting in
substantially higher grain yields. The yield
benefits can continue into later years.
"While this method is expensive, at
more than $50 a hectare, the cost would
be spread over eight to 10 years for whole
paddock inversion, or 10 percent a year
where only the windrow is buried," says Dr
Peltzer. "Soil inversion is a disruption to
conservation tillage practices, which should be
implemented in the years between inversions."
Dr Peltzer says re-inversion would not
bring up any viable ryegrass seed after about
eight to 10 years, but other species, such as
wild radish and wild oats, may still be viable, although this has not been confirmed.
The other weapon against weeds that is
being extensively studied in WA is the role
of ants as biological control agents. The
department’s David Minkey says ants can
eat their way through thousands of seeds
from the soil surface. However, trials show
that while this method costs nothing, control
rates can range from zero to 100 percent.
Mr Minkey notes that although it is a noninvasive,
non-chemical method, biological
control by ants may limit the use of some
other farm practices such as insecticide use
and tillage. Weed seed predation is usually
higher on lighter soils and more effective
on lupins, barley or pasture, compared
to canola and wheat residues, he says.
GRDC Research Codes:
UWA266, DAW613, DAW492.
For more information:
Dr Sally Peltzer, 08 9892 8504,
David Minkey, 08 9622 1902,
Dr Michael Walsh, 08 6488 7872, email@example.com