Technical highlights - Department of Primary Industries ...

18. Ecology and control of national weed eradication targets
Project dates
July 2008 – June 2013
Project leader
Simon Brooks
Tropical Weeds Research Centre
Tel: (07) 4761 5708
Email: simon.brooks@deedi.qld.gov.au
Other staff in 2010–11
Shane Campbell, Wayne Vogler, Kirsty
Gough, Stephen Setter, Katie Patane and
Sharon Rossow
Objectives
• Investigate key ecological attributes
influencing the eradication of species
targeted by national cost-share
eradication programs.
• Refine eradication methods by using
ecological information.
• Investigate alternative control methods
for remote Siam weed infestations in
the seasonally dry tropics.
Rationale
Siam weed (Chromolaena odorata) is a
Class 1 declared weed in Queensland
and has been the target of a national
cost-share eradication program since its
discovery in the wet tropics region of
northern Queensland in 1994. It has also
been found in the upper Herbert River
catchment (1997) and in the upper Ross
River and Black River catchments west
of Townsville (2003).
The National Four Tropical Weeds
Eradication Program commenced in
2003, targeting four genera of Class 1
weeds (Clidemia hirta, Limnocharis
flava, Miconia calvescens, M. nervosa,
M. racemosa and Mikania micrantha),
which are located primarily on the wet
tropics coast of Queensland.
These eradication programs will only
be successful if field crews can locate
all individuals of each species, apply
effective control measures, prevent new
seed production and monitor infestations
until the seed bank is exhausted. To
address queries from the eradication
programs, our research concentrates on
key biological parameters (soil seed bank
persistence, age to maturity, flowering
behaviour, seed production and dispersal
vectors and barriers) and on effective
control methods for each species.
Methods
Specific questions investigated by this
project and the trials to address them are
outlined below.
Are the key Siam weed biological
characteristics of age to maturity and
seed longevity the same in seasonally
drier, warmer areas as they are along the
wet tropics coast?
• Siam weed seeds sourced from
infestations in the wet and dry tropics
are germinated in the quarantine
laboratories at the Centre for Wet
Tropics Agriculture (CWTA) and
TWRC and seedlings are planted in
pots at monthly intervals for one year.
We collect data on growth rates and
flowering behaviour and the plants
are destructively harvested as they
mature.
• We bury fresh Siam weed seed from
an infestation near Townsville in
permeable mesh packets to investigate
the effects of burial duration, grass
cover, soil type and burial depth
in a dry tropics environment at
TWRC. Packets are retrieved every
6–12 months until no viable seed
is recovered. Previous research has
shown that viable seed is exhausted
7 years after burial in a wet tropics
environment.
Can larger Siam weed plants be controlled
by repeated burning and how do repeat
fires influence the soil seed bank?
• We maintain monitoring plots
within a large Townsville Siam
weed infestation and subject them
to repeated controlled burns.
Pre-burn data collected includes
plant size, fuel loads, soil seed banks
and soil moisture levels. Post-burn
assessments include fire damage and
mortality of Siam weed, sizes of soil
seed banks and seedling recruitment.
Can Siam weed be effectively treated
with a low-volume, high-concentration
herbicide application through a splatter
(gas) gun?
• Some infestations in remote or
rugged country cannot be treated
with high-volume foliar herbicide
applications and there has been
a reliance on manual control. We
conduct investigations into the use
of a splatter gun herbicide applicator.
This equipment can be carried in
a backpack and relies on a higher
concentration of herbicide in a lowvolume
application.
How long will seeds remain viable when
immersed in creek water and will this
survival influence search buffers? Is sea
water a barrier to the dispersal of viable
Siam weed and limnocharis seeds?
• All national weed eradication target
species occur along creek lines. In a
seed immersion trial in the ecology
laboratory at CWTA, we compare
the seed viabilities of L. flava,
C. hirta, M. calvescens and two seed
collections of Siam weed immersed
for 2–126 days in creek water, sea
water and a 50/50 mix. Results will
provide baseline data for models of
aquatic dispersal. We also conduct
laboratory investigations into seed
buoyancy and seed germination under
increasing levels of salinity.
How persistent are L. flava, M. calvescens
and C. hirta soil seed banks?
• Soil cores are collected regularly
from an area with a high density of
M. calvescens (prior to control) at
the El Arish infestation. Seed bank
studies for L. flava are continuing at
an infestation in a constantly wet,
spring-fed, lowland tropical stream
near Feluga. This data will guide the
duration of control and monitoring
activities, as there is no other
information available on limnocharis
seed persistence. All soil samples
are sieved to remove, count and
germinate seed.
• We also bury C. hirta and
M. calvescens seed in permeable
mesh packets to investigate the
effects of burial duration and depth
in a wet tropics environment at
CWTA. Packets are retrieved every
6–24 months until no viable seed is
recovered.
Part 2 Landscape protection and restoration 39