Bushland Weeds Manual - Environmental Weeds Action Network

48
Chapter 4 Corms, Bulbs and Tubers Case Studies
Case study 4.3 Control of Taro (Colocasia esculenta) and subsequent regeneration of the
native plant community – a case study from along the Gingin Brook
Illustration: IFAS Center for Aquatic
Plants 1996.
The study site was located along a
section of the Gingin Brook in the
town site where Swamp Paperbark
(Melaleuca rhaphiophylla) and
Flooded Gum (Eucalyptus rudis)
form the main overstorey in the
fringing vegetation and Tall Sedge
(Carex appressa), Tassel Sedge
(Carex fascicularis) and the fern
Cyclosorus interruptus the
understorey. Where Taro invades it
completely displaces the
understorey and allows no
regeneration of overstorey species.
Small population of Taro, before treatment
May 1999.
Physically removing isolated
population in summer 1999
Physically removing small (up to 10
m x 10 m) outlying populations, was
initially tried in the summer of 1999.
The work was quite labour intensive
with corms weighing around five
kilos and the biomass left to dispose
of significant. Follow-up work was
required for the next two years and
involved removing small plants that
was regrowth from pieces left
behind. Although effective on smaller
populations, physical removal was
not practical for larger infestations.
Herbicide treatment in the
summer of 2000
In December 2000, following some
preliminary trials, all Taro (around
one hectare) was cut to the base
and the bases painted with a 50 %
glyphosate solution. These plants
were up to two to three meters high
and beyond the reach of a backpack
unit. Six weeks later the regrowth,
less than one metre high, was
carefully spot sprayed with a 2 %
glyphosate solution + metsulfuron
methyl (0.05 g/L + Pulse ® 2 mL/L). A
small 750 mL hand held sprayer was
used to carefully target Taro
regrowth. The glyphosate provided
a relatively fast knock-down of top
growth so the area covered could
easily be seen.
A bare open patch was left following
removal in February 2000.
Results from the
monitoring transect
Information collected along a
transect run from the native
vegetation into the Taro infestation
showed the treatment was
effective (Table 1).
Regeneration of the native plant
communities – photo points
from the preliminary trials
Preliminary trials over the summer
of 1999/2000 provided the basis to
treat the entire population of Taro in
this way. Fixed photo points at those
trial sites showed the treatment was
effective. In addition, they showed
rapid regeneration of the native
plant community. Photo points can
provide useful information when the
changes are visually dramatic and
the plant community relatively
simple. In this case the plant
community went from almost 100 %
cover of Taro to 100 % cover of
native species over a couple of
years. Only six species of natives
made up that cover; Tall Sedge,
Tassel Sedge, Swamp Paperbark and
Flooded Gum all spread by seed,
often in water flow, while Cyclosorus
interruptus and Native Knotweed
(Persicaria decipiens) spread rapidly
by vegetative means.
Source: Brown and Brooks (in
press b).
By May 2001 native sedges, ferns and
seedling paperbarks had colonised the
open ground.