Bushland Weeds Manual - Environmental Weeds Action Network

Number of Watsonia
Chapter 4 Corms, Bulbs and Tubers Case Studies
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Figure 1. Number of Watsonia meriana in
plots (1 m x 1 m) along a transect through
the population in Shenton Bushland in 1999,
2000 and 2001.
Brixton Street Wetlands
1999
2000
2001
0 20 40 60 80
Distance along transect (m)
Introduction and spread: There
are at least four species of Watsonia
in the Brixton Street Wetlands;
W. borbonica, W. versfeldii,
W. meriana and W. meriana var.
bulbillifera. At present only
W. meriana and W. meriana var.
bulbillifera form dense infestations.
Garden refuse, soil movement and
work along the adjoining railway
line could all have brought in seed
and vegetative material. Seed or
cormels may also have come in
with water movement or birds.
Spread appears to be mainly by a
slow expansion of populations via
corms, cormels and possibly
seed. Occasionally however,
isolated plants are found 100
metres or more from the main
population in undisturbed bushland
indicating cormels or seed are
dispersed by birds, other animals
or human activity.
Distribution: Only a few scattered
plants of W. versfeldii and
W. borbonica have been found in the
wetlands. The one dense infestation
of W. meriana that was invading the
highly disturbed area of Viminaria
shrubland has been eradicated by
the Friends of Brixton Street. The
focus of this study was a dense
infestation of W. meriana var.
bulbillifera invading understorey of
the Marri woodland.
Response to treatment: The
number of W. meriana var.
bulbillifera plants remaining after
two years treatment (Figure 2)
indicates that intensive follow-up
will be required for a number of
years in this site also. Once again
much smaller plants arising from
small corms not seed, made up the
population in the years following
the initial treatment.
Number of Watsonia
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0 10 20 30 40 50
Distance along transect (m)
Figure 2. Number of Watsonia meriana var.
bulbillifera in plots (1 m x 1 m) along a
transect through the population in Brixton
Street Wetlands, 1999, 2000 and 2001.
Talbot Road Bushland
Introduction and spread: Bulbils
or seeds may have come in on
maintenance machinery doing
works along a drain near the main
infestation. Water and soil
movement may also have brought
material in. Movement into good
bushland appears to have been
facilitated by soil disturbance
associated with track maintenance.
Distribution: A dense infestation
of W. meriana var. bulbillifera
occurs in disturbed Marri woodland
on the eastern boundary, extending
into good bushland for around 40
metres. Occasional isolated plants
are found in undisturbed bushland
a long way from the main
infestation suggesting birds or other
animals are playing a role in spread
of cormels and perhaps seed.
Response to treatment: The
population of W. meriana var.
bulbillifera was effectively
controlled in the first year of
treatment. No smaller plants came
back into the sites and the small
amount of follow-up required was
on large plants missed the first time
around (Figure 3).
What do the results tell us?
1999
2000
2001
Watsonia meriana var. bulbillifera
responded quite differently to
treatment at Talbot Road than at
Brixton Street. It appears this is
because the population at Talbot
Number of Watsonia
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300
250
200
150
100
50
0
1999
2000
2001
0 10 20 30 40 50
Distance along transect (m)
Figure 3. Number of Watsonia meriana var.
bulbillifera in plots (1 m x 1 m) along a
transect through the population in Talbot
Road Bushland, 1999, 2000 and 2001.
Road was initially sprayed with a 1
% solution of glyphosate rather
than wiped with 10 % solution, but
site differences may also have
played a role. Brixton Street is a
denser population on a much
wetter site. Whatever the cause,
intensive follow-up will be required
at the Brixton Street site for a
number of years. Spraying
glyphosate is not an option in
bushlands where Watsonia grows
closely among native flora. The
Shenton Bushland population of
W. meriana is also going to require
intensive follow-up for a number of
years. Why large numbers of
smaller plants continue to come up
each year at this site also is difficult
to explain – age and density of the
population and site conditions may
all be playing a role.
Understanding the biology of
Watsonia and monitoring
populations is clearly important if
this weed is to be effectively
managed. This case study highlights
the importance of assessing invasive
weeds on a site-specific basis and
the necessity of resources to be
made available over the long term.
The results of the monitoring also
provided the impetus to look for
more effective methods and trials
with the herbicide Dalapon (2,2-DPA)
in Shenton Bushland are looking
promising. This herbicide has been
used on roadside populations of
Watsonia in the Albany region for
many years (J. Moore pers. comm.).
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