Bushland Weeds Manual - Environmental Weeds Action Network

42
Chapter 4 Corms, Bulbs and Tubers
Targeted application techniques
Sometimes the only option for effective control is a
non-specific herbicide such as glyphosate. The
herbicide needs to be carefully targeted so that only
the weed, often growing closely amongst native
vegetation, is treated. An example of a successful
targeted application technique in practice is the
effective control of Watsonia invading native bushland
on the Darling Scarp (Day 1993). Using a 500 mL spray
bottle with a sponge wired over the nozzle, a 10 %
solution of glyphosate is wiped onto individual leaves
just before flowering, at corm exhaustion. Community
volunteers have controlled large populations of Watsonia
and contained the spread of the weed using this method.
The effectiveness of this treatment was recorded at
three bushland sites
across the Swan
Coastal Plain from
1999-2001 with some
interesting results
(case study 4.2).
Wiping Watsonia leaves in spring in
Shenton Bushland.
Biological control
For the smaller
cormous and bulbous
species wiping leaves
of individual plants is
not practical. In
Shenton Bushland for
example there were
up to 1700 bulbs of
Yellow Soldier in a
single 2 m x 2 m plot.
With limited resources
available wiping
individual plants was
not an option (case
study 4.1).
Biological control is presently available for Bridal
Creeper. In 1999 CSIRO released a leafhopper that
weakens the plant by sucking sap, causing a silver
patterning on leaves and reducing seed set. It is a very
useful tool for preventing the spread of large
infestations that are either inaccessible or beyond the
resources of current control programs. A rust fungus
has been released and is also available for the control
of Bridal Creeper. Infected plants shed leaves early and
are severely weakened. The rust is slow to spread
through established populations of Bridal Creeper.
Recording effectiveness of control methods
and regeneration of native plant communities
It is important to have in place objective methods for
assessing effectiveness of control methods over time
so treatments and management strategies can be
adjusted accordingly.
• Maps of a particular weed species in a patch
of bush: These provide good base line
information for a control program, and over time,
if updated, will provide a record of the
effectiveness of that program.
• Fixed photo points: Although an interesting
record, fixed photo points do not provide
quantitative information on the overall success of
the program or the degree of follow-up required.
They also provide very limited information on the
impact of a control program on the native plant
community. As long as the limitations are
recognised, photo points can be a useful tool for
recording change over time. Photos were
particularly useful for recording the highly visable
changes that occurred following removal of Taro
along the Gingin Brook, (case study 4.3), and for
recording the change in Watsonia treatment sites,
as long as they were accompanied by a detailed
species list. They were not so useful for recording
change following the removal of smaller cormous
weeds such as Harlequin Flower in the diverse
plant communities at Brixton Street.
For more information Elzinga et al. (2001) provides
very detailed information on setting up photo point
monitoring and studies where repeat photography has
been used to monitor long-term change.
Importantly though, distribution maps and photos will
not record in any detail changes in weed populations.
Recording the density and frequency of particular
weeds from year to year is often vital in assessing the
effectiveness of a control program. Also, when
undertaking any weed management program in
bushland, the focus is not simply on eliminating weeds
but on protection of intact native plant communities. It
is important to have an understanding of what impacts
the control work is having and what moves in once the
target weed/s have been controlled. In the incredibly
diverse flora of south west Western Australia this can
be a complex task. At one site on the eastern side of
the Swan Coastal Plain there are over 300 native plant
species in only 19 hectares and up to 80 in a 10 m x 10
m plot. It is important to know and understand these
systems if they are to be managed effectively for nature
conservation. Some methods used to collect
information on change over time in populations of
weeds that die down to underground storage organs
and co-occurring native species are described in case
studies on Yellow Soldier (case study 4.1), Watsonia
(case study 4.2), Taro (case study 4.3) and Harlequin
Flower (case study 4.4).
Note: With bulbous, cormous and tuberous weeds, until they begin
active growth in the growing season following herbicide application,
it is often not possible to know how many plants including the
storage organ, have been killed. It may be nine months after
treatment before you can assess effectiveness of a control program.
Key points
• South African geophytes are one of the most
serious groups of bushland weeds in south west
Western Australia.
• Once established on disturbed edges they can
invade relatively undisturbed bushland, generally
via seed or cormels, form dense monocultures and
displace native plant communities.
• Fire appears to facilitate establishment of
seedlings and expansion of populations.