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Wild radish
Beating herbicide resistance in wild radish
by Toni Commens,
CO-OPERATIVE RESEARCH CENTRE FOR
WEED MANAGEMENT SYSTEMS
F
ast-developing resistance to herbicides by
wild radish has forced producers to tackle
the weed using a combination of control
methods.
This extremely competitive weed, which can
reduce wheat yields by up to 20 per cent,
already is resistant to the major weapon used to
combat it — Group B herbicides. Researchers
also fear wild radish’s resistance may be
transferred to other weeds by outcrossing
(breeding with other plant species).
The solution to effective wild radish control
lies in preventing seed production and reducing
the existing soil seedbank. This can be done by
adopting a variety of cultural, chemical and
biological approaches.
Distribution
Wild radish is a major weed of winter grain
crops and, to a lesser extent, pastures in
southern Australia. It is is distributed in a
broad band from south eastern Queensland,
through New South Wales, Victoria, Tasmania
and South Australia, and is widespread in the
cereal cropping areas of Western Australia (see
Figure 1 on page 39).
In WA, wild radish is rated as one of the
most troublesome weeds of broadacre
cropping, particularly in the wheat-lupin
rotation which dominates the northern
wheatbelt. In NSW, wild radish infestations
occur in the higher rainfall areas of the
southern wheatbelt and along the western
slopes of the Great Dividing Range, and is
becoming increasingly problematic.
In Victoria wild radish is a significant weed
of crops in the north east and western district
and in the cropping areas of the Gippsland, as
well as the high rainfall and intensive cropping
areas of SA.
One of the reasons for the wide distribution
of wild radish is its prolific seeding — it can
produce up to 17,000 seeds per square metre.
It also competes vigorously with crops.
Densities of 10 wild radish plants per square
metre can reduce yields in wheat by up to 20
per cent.
While livestock readily eat the weed, losses
attributed to wild radish poisoning are rare.
The seeds are the most dangerous part of the
plant. When deaths have occurred, postmortem examinations have revealed jaundice,
anaemia and liver damage.
Animals may become affected when
confined to areas where wild radish is
abundant. Symptoms include initial loss of
appetite, weakness, stupor and paralysis. Some
may become very excitable. Dung is covered
with mucus and as the animal’s condition
worsens watery blood-stained diarrhoea is
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Wild radish plants are prolific seeders and very competitive. Wild radish can produce up to 17,000 seeds
per square metre and densities of 10 wild radish plants per square metre can reduce yields in wheat by
up to 20%.
evident. The symptoms are often confused
with copper poisoning. Reportedly, up to half
affected animals die within three to five days
while animals that survive will take up to 10
days to recover fully.
Wild radish is very competitive during the
early growth stages of crops. The initial flush
of germination at the start of the season
following cultivation is the most prominent.
The remaining dormant seeds germinate
sporadically after rain.
✔
Wild radish is a problem weed in
cropping and pasture areas
throughout Australia.
✔
Long-term wild radish control can
be achieved by integrating cultural,
chemical and biological methods to
reduce the existing soil seedbank
and seed production.
✔
Useful cultural practices include
cultivation, spray-grazing and
slashing, hygiene (cleaning
machinery and sowing clean seed)
and crop swathing.
✔
Thoughtful use of herbicides as
part of an overall management
plan is advised as wild radish
already has developed resistance
to Group B chemicals.
The fibrous stems of wild radish make
harvesting difficult by choking the header
comb. The damaging effects of green plant
material also can reduce stored grain seed
quality, especially lupin or peas.
Characteristics
Characteristics that enable wild radish seeds
to survive and remain as an agricultural weed
are dormancy and longevity (persistence).
Wild radish seeds are dormant at the time of
production and, by the start of the cropping
season, as much as 70% of the seeds are still in
a state of dormancy due to the protective seed
pod.
Other factors influencing wild radish seed
dormancy are geographical location and
temperature. Seeds from WA’s warmer
northern agricultural districts have lower
dormancy levels than seeds from cooler
southern districts.
Wild radish seeds have a relatively long life
span. Seeds buried to 100 millimetres may
remain viable for up to six years.
The majority of seeds will germinate during
autumn and winter. Optimum temperature for
germination is 20 degrees Celsius, but if soil
moisture is adequate, germination can occur at
any stage during the growing season.
Temperature is the major factor controlling
plant development to flowering, while day
length and temperature will influence the
duration of flowering. The appearance of first
flowers and the duration of flowering depend
on the time of seedling emergence.
The primary means of seed dispersal is as a
contaminant of agricultural produce, especially
in seeds and hay. Seeds also are spread by
wind, water, livestock and by adhering to
machinery. As wild radish is an outcrossing
plant, bees can carry pollen over long
FARMING AHEAD No. 68 - August 1997
Wild radish...
TABLE 1 Herbicides registered for use in major cereals, pulse crops and pastures
Herbicide
Crop
Time of application
Chemical group
bromoxynil
all
Z12-15
C
chlorsulfuron
wheat
barley, oats
PPI, Z11+
Z12+
B*
Comments
CEREAL CROPS
Mainly used in mixtures
diflufenican
all
Z12+
F
Used in mixtures
diuron
all
Z13-16
C
Used in mixtures
diquat
all
ripening
L
Pre-harvest, dessication
flumetsulam
all
Z12+
B*
linuron
all
Z13-16
C
Used in mixtures.
MCPA
all
Z13-37
I
Used in mixtures, for early application
Used in mixtures
methab’thiazuron
all
Z13-16
C
metosulam
all
Z12+
B*
metribuzin
barley
PSPE-Z13
C
prometryn
all
Z13-16
C
terbytryne
all
Z13-16
C
Used in mixtures
thifensulfuron
wheat, barley
Z12+
B*
Used in mixtures with metsulfuron
triasulfuron
wheat
barley, oats
PPI, Z12+
Z12+
B*
2,4-D
all
Z15-37
atrazine
lupin
bentazone
cyanazine
diflufenican
Used in mixtures
I
Late application
PPI
C
Used with simazine
faba beans
2-leaf stage
C
Some crop effects
chickpea, faba beans,
field pea, lentil
PPI, 2-3 leaf stage
(faba beans)
C
Safe but may have problems with
effectiveness
lupin, field peas
pre-emergence,
2-4-leaf stage
F
Good control
diuron
lupin, field peas
pre-emergence
C
May have problems with effectiveness
flumetsulam
field peas
2-4-leaf stage
B*
Some crop effects
imazethapyr
faba beans, field peas
pre-emergence
B*
MCPA, MCPB
field peas
2-4-leaf stage
I
Some crop effects
metosulam
lupin
8-leaf stage
B*
Some crop effects
metribuzin
chickpeas, faba beans,
field peas, lupin
pre-emergence,
2-leaf stage
C
prometryn
field peas
pre-emergence
C
May have problems with effectiveness
simazine
chickpeas, faba beans,
lupin
PPI, pre-emergence,
2-4-leaf stage
C
Herbicide of choice
bromoxynil
subclover, lucerne
post-emergence
diflufenican
subclover, lucerne
post-emergence
F
Used in mixtures
diuron
subclover, lucerne
post-emergence
C
Used in mixtures
diquat (+paraquat)
lucerne
post-emergence
L
Lucerne must be one year or older
flumetsulam
all
post-emergence
B*
imazethypyr
subclover, lucerne
post-emergence
B*
MCPA
subclover
post-emergence
I
methab’thiazuron
subclover
post-emergence
C
terbytryne
subclover
post-emergence
C
terbacil
lucerne
post-emergence
2,4-D, 2,4-DB
subclover
post-emergence
PULSE CROPS
PASTURES
C
I
Used in mixtures
Spray-graze
Spray-graze
* Some wild radish populations have been shown to be resistant to all Group B herbicides.
Source: David Bowran, Agriculture WA
The Co-operative Research Centre for Weed Management Systems makes no warranty of any kind, expressed or implied, concerning the use of products or active constituents mentioned in
this table and article. Consult labels and seek local advice before use.
FARMING AHEAD No. 68 - August 1997
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Wild radish...
distances. Already herbicide resistance in wild
radish is approaching dangerous levels and it is
particularly worrying that this resistance could
be transferred to other populations.
To achieve long-term control of wild radish,
seed production must be prevented and the
existing seedbank in the soil reduced. As with
other weeds, integrating cultural, chemical
and biological controls is encouraged.
FIGURE 1 Wild radish distribution
Cultural management
The biological characteristics of wild
radish favour the integration of a number of
cultural control practices for management in
cropping and pasture systems. These include
cultivation, spray-grazing and slashing,
hygiene and crop swathing
Cultivation: Shallow burial of wild radish
seed to a depth of 10 to 50mm results in the
greatest emergence of wild radish. One or two
years of cultivation to achieve maximum
germination, followed by conditions of
minimum soil disturbance in subsequent years,
will reduce wild radish seed reserves. It will be
necessary to ensure that later cultivations do
not bring buried seed back close to the surface
where it could germinate.
The use of a mouldboard plough to achieve
deep burial of the seed in the first year,
followed by direct drilling or shallow
cultivation during years two to four also will
reduce wild radish populations in crops
significantly. But the use of a mouldboard
plough over large areas will have limitations.
Spray-grazing and slashing: Spray-grazing
involves spraying the pasture infested with
wild radish at the rosette stage, with sub-lethal
rates (500 grams per litre at 350 millilitres to
1.4L per hectare) of 2,4-D or MCPA, waiting
for seven to 10 days and grazing heavily with
sheep. Subclover is the legume pasture most
tolerant of these rates.
These rates do not kill the weed outright, but
improve palatability by mobilising sugars in
the plant. The weed is then preferentially
Chemical management
Source: Parsons and
Cuthbertson, 1992
grazed. If adequate stocking rates
are used, the weed growth and seed
production will be reduced severely. Take care
not to overgraze desirable legume species. As
wild radish produces flowering stems and
seeds rapidly, slashing needs to be repeated
frequently to reduce seed production.
Hygiene: Hygiene is vital in preventing the
spread of wild radish. Cleaning cultivation and
harvesting equipment, sowing clean seed,
quarantining stock likely to have consumed
wild radish seeds recently and feeding weedfree fodder will reduce the risk of spreading
wild radish. Toxic or noxious weed seeds are
prohibited by state laws from being used in
stockfeeds.
The damaging effects of green plant
material, especially in stored lupin or pea seed
also should be an incentive to produce and
purchase weed-free seed. Grain to be used for
sowing should be obtained from wild radishfree paddocks or seed should be cleaned to
remove as much of the weed seed as possible.
Crop swathing: Where green wild radish is
likely to be present at harvest, delays can be
avoided by swathing or windrowing the crop.
This protects the crop from shattering and wind
Wild radish appearance
This two-leaf wild radish seedling shows the
distinct characteristics of the weed: classic heartshaped cotyledons, obvious veins on leaves and
stiff hairs. The weed has a distinct radish taste.
FARMING AHEAD No. 68 - August 1997
damage and allows the green wild radish to dry
off with the crop, overcoming problems
associated with harvesting crops containing
green wild radish. Swathing is a useful
management tool but it does not reduce wild
radish seed carryover unless the seed is trapped
and removed at harvest.
Other measures such as hand weeding,
hoeing or burning may work in situations
where odd plants appear in previously wild
radish-free areas. This will help to prevent
any build-up of wild radish infestations.
Wild radish is a member of the Brassicaceae
or mustard family. It is an erect annual herb
growing up to 1.5 metres high. It grows best
in highly fertile soils, in moderately exposed,
cool to warm sites up to subalpine levels. In
cooler regions, wild radish may take two years
to complete its lifecycle.
Wild radish cotyledons are heart shaped and
hairless. The first leaves are oval shaped, have
a round apex and a toothed margin. These
leaves are covered with short stiff hairs. Leaves
at the base of the plant have a strong turniplike odour when crushed.
The plant develops as a flat rosette and
branches from near the base as it matures.
The upper stem leaves are narrow, shorter and
often undivided.
Wild radish flowers are pale yellow, purple,
white or cream with purple veins in the petals.
Wild radish is an extremely competitive
weed. Early control when it is most susceptible
to herbicides, and before it competes strongly
with the crop, will help to avoid major yield
losses. Often the weed is sprayed when present
at low densities and sometimes with multiple
applications in the same season. Repeated
applications of Group B herbicides (especially
multiple use of herbicides such as
chlorsulfuron) to control wild radish will result
in wild radish and other weeds rapidly
developing herbicide resistance to Group B
chemicals. About 80% of herbicide resistance
tests held by Agriculture WA on spray failures
in the 1996 season showed resistance to Group
B herbicides.
Knockdown herbicides containing chemicals
such as glyphosate, paraquat and diquat are
registered for seed-bed establishment in a
range of crops.
A wide selection of herbicides is available for
use in cereals. Treatments registered for early
control of wild radish in most cases will prove
effective in removing competition and
providing yield increases. Applications for
control of later emerging plants may not result
in yield increases, but can reduce seed set, assist
in harvesting and maintaining grain quality.
Although a number of products is available
for pre-emergence application in pulses, the
range of herbicides for use in chickpea, faba
beans and lentils at post-emergent timings is
limited. The poor effectiveness of triazines on
wild radish, in lupin crops in particular, usually
is related to limited soil moisture at
germination. No-till cropping and stubble
retention will impact on the effectiveness of
pre-emergent herbicides. There are currently
no in-crop herbicides available for use in nontriazine-tolerant canola. Simazine, atrazine
and possibly cyanazine and metribuzin, all
Group C herbicides, are available for wild
radish control in triazine-tolerant canola.
Herbicides such as bromoxynil (Group C),
MCPA (Group I) and bromoxynil+MCPA are
available for use in linseed or linola crops.
There is a range of herbicides registered for
controlling wild radish in cereals, pulse crops,
and pastures (see Table 1).
Acknowledgements: Jim Dellow, NSW Agriculture; Aik Cheam, David Bowran, John Holmes,
Agriculture WA; Ross Britton, PISA; John
Matthews, CRC Weed Management Systems;
National Agricultural Commodities
Marketing Association.
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