Bushland Weeds Manual - Environmental Weeds Action Network

Slashing leaves and stems
Repeated removal of leaves and stems of some species
of weedy geophytes over time can reduce population
density, reproductive output and plant vigour. It is
generally labour intensive, however, and often not
effective in the longer term. The few examples below
illustrate where it can be a useful tool, under certain
circumstances.
• If Bridal Creeper is slashed back to the stem bases
every month over the growing season for several
years plants are severely weakened (J. Moore
pers. comm.). In bushland on Garden Island, just
off the coast of Perth, continual grazing by
Tammar wallabies has prevented Bridal Creeper
from becoming wide-spread on the island
(Keighery 1993).
• Trials in the fringing vegetation along Bennett
Brook in Perth suggested that slashing Arum Lily
back to the base every month over the growing
season can, in the short term at least, greatly
reduce the number of adult plants in a population.
Plants were slashed to the base every month for
seven months over the 1999 growing season. Over
80 % of plants in the population did not resprout in
the 2000 season (Brown unpubl). The slashing was
done by hand with a sharp hoe and would be very
labour intensive over a broad area. The work
would need to continue over a number of years
and if left for any length of time populations would
probably quickly return to pre-treatment levels.
• Work in South Australia has found if Bulbil
Watsonia plants are slashed at 15 centimetres or
less above the ground, at the first sign of a flower
spike, neither flower spike nor bulbils will be
produced in that year. In addition the plant will
form smaller corms the following year (Wilson and
Conran 1993).
Note: simply removing flower spikes to prevent seed set can
sometimes lead to more vigorous plants the following year. Work on
Pink Gladiolus in south west Western Australia found that removal of
flowers just as they were opening resulted in a larger replacement
corm (and presumably more vigorous plants that would be harder to
kill) the following year (Hocking 1992).
Chemical control methods
Chemical control of bulbous, cormous and tuberous
weeds is often the only practical option available for
dense infestations invading good bushland. It can be
practical on a large scale, avoids soil disturbance and
prevents soil erosion.
Herbicide application needs to be done by experienced
operators with the correct equipment, knowledge of
herbicides and an understanding of bushland and of
the native flora. Regardless of the herbicide,
application needs to be carefully timed to be effective
on many of the species dealt with in this chapter,
particularly the annually renewed bulbs and corms
(Box 4.4).
Note: Anyone applying herbicides should have appropriate training
in the safe use and handling of relevant chemicals (Chapter 8).
Chapter 4 Corms, Bulbs and Tubers
The herbicides
Important note: The following herbicides are currently the subject
of a minor use off-label permit in non-crop situations in Western
Australia. Application must comply with all conditions of the permit.
Available from: (http://permits.nra.gov.au/PER4984.PDF).
Glyphosate
When applied at the correct stage of the life-cycle, this
non-selective herbicide has been found to be effective
against a number of South African bulbous, cormous
and tuberous species. These include Freesia (Freesia
alba x leichtlinii), Ixia species (Dixon and Keighery
1995), Watsonia (Day 1993) and Bridal Creeper
(Pritchard 2002). Glyphosate is an acceptable option
where the weeds occur in dense monocultures on the
disturbed edges of bushland. However these weeds
often grow closely amongst native vegetation and the
use of non-selective herbicides can lead to
unacceptable off-target damage unless the application
method is very carefully targeted (Box 4.2 and Box 4.3).
Metsulfuron methyl
Following the introduction of the sulfonylurea group of
herbicides in early 1980s, metsulfuron methyl (Brushoff
® , Ally ® ) in particular has been found to be very
effective against a number of South African
bulbous/cormous species. These include Soursob
(Peirce 1998), Bridal Creeper (Pritchard 1991, Dixon
1996), Freesia (Dixon 1998b), Harlequin Flower (Meney
1999, Brown and Brooks in press c) and Yellow Soldier
(Brown et al. 2002). Interestingly, some of these studies
suggest that many native species are resistant to the
effects of metsulfuron methyl at rates of 5 g/ha and
below (Dixon 1996, Meney 1999, Moore 1999, Brown et
al. 2002, Brown and Brooks in press c). This is an area
that requires further study and any use of the
sulfonylurea group of herbicides in bushland needs
very careful consideration. Metsulfuron methyl can
remain active in dry alkaline soils and is absorbed by
roots for many months following application (Parsons
1995, Noy 1996, Sarmah et al. 1998).
Chlorsulfuron
Also of the sulfonylurea group of herbicides,
chlorsulfuron (Glean ® ) is known to be effective on
Arum Lily (Moore and Hoskins 1997), Cape Tulip
(Parsons and Cuthbertson 2001) and Harlequin Flower
(Brown and Brooks 2002). The impacts of chlorsulfuron
on native plants that co-occur with these weeds are
not well understood. Trials on Harlequin Flower
invading herb-rich shrublands in the Brixton Street
Wetlands indicated chlorsulfuron had an impact on
some native herbs (Brown and Brooks in press c).
Important note: Both metsulfuron methyl and chlorsulfuron can
inflict damage to vegetation at very low concentrations. Both can
remain active in the soil for some months following application. They
should only be spot sprayed on target species invading native
bushland and always by well-qualified responsible operators with a
thorough knowledge of the native flora.
2,2-DPA
Reported to successfully control Watsonia invading
remnant native vegetation. Sprayed at a rate of 10 g/L,
2,2-DPA has little impact on a range of native species
(Moore and Fletcher 1994, Brown and Brooks unpubl.).
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