Aquatic weed research for
more efficient water delivery
Sigrid Tijs
Research & Development Coordinator, Murrumbidgee Irrigation
IN A NUTSHELL
z Sagittaria is an aggressive aquatic weed that impedes water flow in channels and drains, and limits the potential
of modernised water delivery systems.
z There is only one herbicide option to control submerged sagittaria (and other submerged weeds), and it has a
significant withholding period, presents risks to people applying the herbicide, and increases the potential for the
development of herbicide resistance.
z A new research project is investigating an alternative herbicide option, which does not have an irrigation
withholding period, for aquatic weeds.
z A second project is investigating a range of insects in Australia and the United States of America, with the aim of
identifying a biological control option for sagittaria.
Aquatic weeds are a major threat to irrigated agricultural
productivity, impeding water flow through channels and
altering water availability and quality. Water delivery can
disperse the weeds into new regions, impacting not only
agriculture, but also on native plant and animal habitats.
The genus Sagittaria is an aggressive aquatic invader with two
species now established in most states of Australia. Sagittaria
(Sagittaria platyphylla) grows in a variety of waterways (irrigation
channels, drains, creeks and rivers), as well as in lagoons, dams
and wetlands. Its establishment is favoured by slow moving or
static shallow water.
A close relation of sagittaria is arrowhead. Arrowhead also
establishes in slow moving or static shallow water, such as
marshes and wetlands, but in New South Wales it is most
familiar as a weed of rice crops.
For those who like botanical detail, arrowhead in NSW was
originally named Sagittaria montevidensis subspecies calycina
or S. montevidensis subspecies montevidensis. However, recent
studies indicate arrowhead in Australia was incorrectly labelled
as S. montevidensis and this species now has been identified
as S. calycina.
Aquatic weeds are a major threat to irrigated agricultural productivity, impede water flow through channels, alter water availability and quality, and
threaten the habitats of native plants and animals.
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IREC Farmers’ Newsletter – Large Area No. 186: Autumn 2012
weeds
sagittaria research
Current sagittaria control limited
New herbicides for aquatic weeds
Acrolein is currently the only herbicide registered for the control
of submerged aquatic weeds and it is used by most Australian
irrigation companies. The emergent or above-water parts of
aquatic weeds may also be controlled by glyphosate or 2,4-D,
however this article focusses on research to control submerged
weeds (or parts of weeds) that restrict water flow in channels.
A research program, led by Dr Tony Dugdale, is testing additional
herbicide control options for aquatic weeds by conducting
laboratory and field trials of herbicides shortlisted as potentially
suitable for use in Australia.
Although acrolein is effective on a wide range of submerged
species, it is very toxic to fauna, potentially dangerous for the
people applying it and only provides short-term control of
most weeds (about six weeks). Given that acrolein is the only
herbicide option for submerged aquatic weeds in irrigation
channels, an acrolein-based management strategy for aquatic
weeds presents risks for irrigation companies from both staff
safety and herbicide resistance perspectives.
Sagittaria (S. platyphylla) is a significant weed problem in
irrigation networks of northern Victoria and southern NSW.
Its broad distribution indicates that sagittaria eradication is
no longer feasible and that new management approaches are
required to reduce its impact. Irrigation companies now find
themselves in a situation where they have an aggressive weed
and only limited options are available to control it.
The Department of Primary Industries Victoria, Goulburn–
Murray Water and Murrumbidgee Irrigation are funding
researchers from DPI Victoria’s Weed Sciences Group, along
with collaboration from Colin Campbell Chemicals, to develop
additional options to minimise the effects of aquatic vegetation
in irrigation channels across northern Victoria and southern
NSW. Further, upgrades to irrigation systems (automated flow
regulators and larger irrigation outlets) increase the importance
of managing aquatic weeds so that farmers can take advantage
of the increased flows.
The researchers are tackling this problem from two angles:
1. research into an alternative herbicide, which will improve
safety, provide more operational flexibility and less
dependence on a single supplier for herbicide
2. development of a biological control program for sagittaria.
Preliminary results indicate that formulations of the herbicide
endothal provide effective control of many of the problematic
aquatic species present in south-east Australia, such as ribbon
weed (Vallisneria australis), floating pondweed (Potmogeton
sulcatus), elodea (Elodea canadensis), cabomba (Cabomba
caroliniana) and sagittaria (Sagittaria platyphylla). Furthermore,
endothal has a good toxicological profile and is used in irrigation
channels in the United States of America without an irrigation
withholding period.
Further trials conducted in irrigation channels in collaboration
with Goulburn–Murray Water are determining if endothal
presents a more effective control option than current
techniques. If successful, the data obtained will be used to
register endothal in Australia, and lead to more efficient delivery
of water to irrigators, and be safer for the environment and
those applying the herbicide.
A biological control for sagittaria
A second project, led by Ms Raelene Kwong, aims to progress
the development of a biological control program against
sagittaria (Sagittaria platyphylla) through the selection of safe,
effective natural enemies.
Biological control aims to slow down the rate of weed spread,
reduce the reliance on herbicide usage in waterways and
mitigate the potential development of herbicide-resistance in
sagittaria populations.
An earlier project, initiated by the National Weeds Productivity
Research Program administered by the Department of
Agriculture, Fisheries and Forestry and the Rural Industries
Research and Development Corporation (RIRDC), identified
that seeds are the major means of dispersal for sagittaria, and
provide a target point in the life cycle for biological control.
Preliminary research results indicate that alternative herbicide options to acrolein could provide effective control of many problem aquatic species
in irrigation channels and drains.
IREC Farmers’ Newsletter – Large Area No. 186: Autumn 2012
27
weeds
sagittaria research
While the identification of biological agents targeting seed
production is a critical step towards sagittaria control, the
success of such a strategy requires information from three
different sources:
1.genetic — to determine whether Australian sagittaria
populations contain genotypes that are not recognised by
biological agents
2. reproductive — to clarify the strategies involved in the
annual production of large seed volumes
3. demographic — to identify biological control agents and
understand their impacts on sagittaria in an Australian
context.
This project is part of a current broader sagittaria project
Genetic, reproductive and demographic facilitation of Sagittaria
invasion. It is funded by RIRDC as part of the second phase
of the National Weeds Productivity Research Program and is a
collaborative project with CSIRO (Dr Broadhurst) and La Trobe
University (Dr Susan Hoebee and Dr Trevor Edwards).
The main activities within the broader project to date are
described in the following paragraphs.
Natural enemy surveys
At various locations across the USA, 20 whole plants and
additional flowering stems were collected at each site for
detailed examination. Plants were inspected for diseases,
insects and nematodes, and the degree of damage and attack
on plant parts was recorded. A range of weevil species was found
attacking sagittaria in the USA. These consist of seed feeders
(pictured), which are capable of completely consuming the
flowers and fruit, while other weevils have caused plant death
from feeding within the plant root crowns. Further research is
required to assess the impact of these natural enemies and
their potential for release into Australia.
Sagittaria biology and ecology
The biology and ecology of Sagittaria spp. are being studied
at multiple sites across Australia and the USA. To date, data
has been collected from a total of 34 sites on a range of plant
parameters including plant size, density and reproductive
performance. This information will provide valuable insights into
possible reasons for the weedy nature of sagittaria in Australia.
A weevil larva consuming the seeds of Sagittaria spp. in the USA,
where sagittaria is a native plant, but it does not cause problems in
waterways.
28
Plant samples for molecular analysis
Leaf material has been collected from 65 sagittaria populations
around Australia and the USA to be analysed this year in a
genetic study to determine the origins of sagittaria populations
imported into Australia during the 1950s. This knowledge is
critical in improving the prospects for a successful biological
control program by ensuring that biological control agents are
sourced from sagittaria genotypes in the USA that closely match
those present in Australia.
What’s next?
Both projects are making good progress and work will continue
over the next few years.
Continued support is required for both these projects to ensure
alternative control measures for sagittaria are developed.
DPI Victoria and Irrigation Australia are working together with
irrigation companies to continue and expand the research
project, which aims to allow future registration of endothal in
Australia.
Further reading
RIRDC website:
Genetic, reproductive and demographic facilitation of Sagittaria
invasion
w w w.rirdc .gov.au/programs/national-rural-issues/weeds/rirdcprojects/project-details.cfm?project_id=PRJ-007053
NSW Primary Industries website:
Sagittaria and arrowhead – weed information
w w w.dpi.nsw.gov.au/agriculture/pest s- weeds/weeds/prof iles/
sagittaria
Further information
Sigrid Tijs (Murrumbidgee Irrigation)
E: [email protected] or T: 02 6962 0200
Tony Dugdale (DPI Victoria)
E: [email protected] or T: 03 9210 9251
Rae Kwong (DPI Victoria)
E: [email protected] or T: 03 9785 0171
Mark Finlay (Goulburn Murray Water)
E: [email protected] or M: 0400 220 644
Further research on the natural enemies of sagittaria is required
to assess the potential for their release into Australia to control the
sagittaria in irrigation channels and drains.
IREC Farmers’ Newsletter – Large Area No. 186: Autumn 2012