|
Grains Research and Development
Corporation Crop Doctor
August 13, 2002
A Crop Link brochure just published by
Queenslandıs Department of
Primary Industries illustrates why farmers are being urged
to manage their problem weeds rather than just go out and try to
kill them wherever they appear.
Common sowthistle, also known as milk thistle, is the subject of
the Crop Link and the information and advice it contains largely
comes from University of New England research supported by
growers and the Federal Government through the
Grains Research and Development
Corporation (GRDC).
According to QDPI Toowoomba agronomist Michael Widderick, common
sowthistle is a significant problem weed because:
- it is widespread across
Australiaıs northern grains region northern NSW and
Queensland,;
o it is the most widespread herbicide resistant weed in the
region with several populations resistant to Group B
herbicides, including chlorsulfuron;
- it is the fifth most difficult
weed to control in winter crops;
- its density has increased over
the last five to 10 years, most probably because farmers have
come to rely more on herbicides for weed control rather than
tillage;
- once considered
winter-dominant, now itıs found all year round;
- a single plant in fallow can
produce up to 25,000 seeds whose structure helps their
dispersal by the wind, an event called "seed rain".
"Common sowthistle seeds depend
more on soil water than temperature to germinate, and
germination in the field usually follows significant rainfall
events, at any time of the year," Mr Widderick says.
"Most seedlings emerge from seeds on the soil surface, or within
one centimetre of it. Because a zero till system allows many
seeds to remain on the soil surface, large numbers of seedlings
emerge after rainfall.
"Tillage moves seeds down the soil profile, progressively
reducing the number of seedlings that emerge at the time but
leaving large numbers of seeds buried in the soil, where they
can persist for more than two years.
.
"Subsequent tillage will bring a proportion of seed back to the
soil surface, where it will be able to germinate."
Mr Widderick says the newly published Crop Link doesnıt claim to
have all the answers to control of common sowthistle. Rather it
aims to challenge growers and their advisers to consider the
ecology of the weed in their management plans.
Zero till systems provide an environment favourable to the
germination and emergence of common sowthistle with incomplete
control by herbicides and/or poor crop competition allowing
weeds to survive and continue the growth cycle.
The ultimate goal in sowthistle management should be to deplete
the seedbank, and stop its replenishment, by practices like
stopping seed production along fencelines, headlands and
roadsides, correct application of herbicides and rotation of
herbicide groups, maximising crop competition and
treatment of surviving weeds to prevent "seed rain".
Free copies of the common
sowthistle Crop Link are available from the Queenslandıs
Department of Primary Industries Call Centre on 13 25 23, on 07
3404 6999 interstate.
The Crop Doctor, Professor John Lovett, is managing director of
the Grains Research and Development Corporation (GRDC),
Canberra.
|
