This document discusses potential future solutions for managing aquatic weeds based on experiences in Australia and New Zealand. It describes how aquatic plants can be both useful and problematic in overgrowth. Common aquatic weeds and reasons for controlling them are outlined. Methods for control include various herbicides as well as mechanical and physical removal techniques. Case studies demonstrate successful control of specific weeds like Egeria, Cabomba, and Hydrilla using herbicides in hydrogel formulations or whole lake treatments. Overall, herbicides are seen as useful when applied correctly by experts, but all aquatic weed control requires a tailored approach.

1. SEARCHING FOR POTENTIAL FUTURE SOLUTIONS
FOR MANAGING AQUATIC WEEDS – SOME
AUSTRALASIAN EXPERIENCES
Peter Harper, Bettersafe Pest & Weed Management, Australia
Dr. Nimal Chandrasena, GHD Pty Ltd, Australia
Bill Chisholm Aquatic Plant Control, New Zealand

2. AQUATIC PLANTS ARE USEFUL & BENEFICIAL
In natural systems, such as lakes and ponds, light to
moderate growth of aquatic plants serve useful purposes:
Provide oxygen, food and cover for fish and other
aquatic organisms, and
may stabilize bottom sediment

3. WHAT ARE THE MAJOR AQUATIC WEEDS?

4. WHY CONTROL AQUATIC WEEDS?
• Prevent infection of new water bodies
• Maintain amenity values
• Prevent economic loss, flooding etc.
• Conservation and biodiversity
• Preserve Water quality

5. AMENITY VALUES UNDER THREAT FROM AQUATIC WEEDS
• Power generation
• Irrigation schemes, canals
• Flood control
• Recreational Amenities (Boat ramps, ski lanes etc.)
• Access to waterways
• Water Quality

6. THE PROBLEM:

7. In Australia Only:
 Diquat
 ‘Bi-active’ Glyphosate
 Metsulfuron-Methyl (for Alligatorweed)
 24D amine ( special Permit)
 Acrolein (restricted use)
 Fluridone (SONAR – Registered under
special permit)
 Carfentrazone (SHARK)
THE PROBLEM:
GLOBALLY VERY FEW HERBICIDES ARE AVAILABLE FOR
MANAGING AQUATIC WEEDS IN WATERWAYS
 Imazomox
 Imazapyr
 Endothal
 Triclopyr - amine

8. AQUATIC WEED CONTROL METHODS
Method Costs/Ha ($)
Hand removal $ 7000-10,000
Mechanical digger $ 2500-5000
Roto Tiller $ 2000 (shallow)
Roto Tiller $ 5000 (up to 5 m)
Mechanical Harvester $ 2000-4000

9. AQUATIC WEED CONTROL METHODS
Method Costs/Ha ($)
Suction Dredging $ 15,000-20,000
Nutrient Control (Phoslock) $ 6000-10,000
Bottom Lining $ 5000- $ 15,000
Water level manipulation Varies
Grass Carp $ 750 ($ 25/fish)

10. AQUATIC WEED CONTROL WITH HYDROGEL
• Diquat Gel
• Guar Gum- inert starch additive
• Mixed as a special formulation
• Much less Diquat used; Reduced loss of chemicals
• Guar Gum is from the ground endosperm of seeds of
Guar plant Cyamopsis tetragonolobus (L.) Taub. (Family
Leguminosae)

11. Diquat is a fast-acting contact herbicide
Mainly effective against floating plants and some
submerged plants.
It causes rapid die off of plant shoots not effective in
killing the roots, rhizomes or tubers.
Diquat will bind to particulate matter and dissolved
organic matter which can restrict use in some situations.
The herbicide can also be used effectively with complexed
copper compounds
Diquat

12. AQUATIC WEED CONTROL WITH HYDROGEL
o High MW; Polysaccharide
o Guar is used as binding agent, roughage and stabiliser in
food, bread, cakes and pastries, pharmacy, paper, textile
and drilling industry
oYou probably ate it this morning at breakfast or with tea !

13. HYDROGEL FOR AQUATIC WEED CONTROL

14. LIVERPOOL, AUSTRALIA, GEORGES RIVER – EGERIA CONTROL
WITH DIQUAT GEL
Before After 5000 m2, 15 L Hydrogel
mix $1000.00 AU

15. SUTHERLAND SHIRE, SYDNEY – EGERIA CONTROL WITH DIQUAT
GEL
Before After
500 m2, 3 L Hydrogel
$ 275 ($ 550/ha)

16. CABOMBA CONTROL WITH CARFENTRAZONE –
GLENBROOK LAGOON SYDNEY, NSW

17. Carfentrazone (Shark) is an EW (emulsion in water)
formulation.
It is a rapid-acting, non-translocated, light dependant,
contact herbicide, rapidly taken up by plant foliage
Forms peroxides which attack the cell wall, causing the
cells to collapse and die.
The foliage shows signs of burning within 24 to 48
hours.
Plant death generally follows within 7 to 28 days for
emerged plants and slightly longer for submerged plants.

20. FLURIDONE USE - AT SYDNEY OLYMPIC LAKES FOR HYDRILLA
CONTROL
The Competition and Warm-Up Lakes cover an area of 76
ha; lakes are separated by barriers
The Competition Lake is 2,300 m in length and 167 m in
width. The average depth is 5 m and the volume of water
is 2,112,550 m3 or approximately 2113 mega litres (ML).
3 applications over 56 days
Day 1: 109.8 L,
Day 28:45.4 L,
Day 56 30.3 L) to achieve 42.1ppb
approximate

23. CONCLUSIONS
Herbicides are useful and effective if used correctly
Some can be used selectively at low doses.
Diquat is suited for treatments in water bodies lakes
ponds and rivers and you can selectively target weed
infestations with hydrogel
Carfentrazone and Fluridone are both suitable for
whole water body treatments
We highly recommend that with any aquatic herbicide
treatment you seek expert advice