SEARCHING FOR POTENTIAL FUTURE SOLUTIONS FOR MANAGING AQUATIC WEEDS – SOME AUSTRALASIAN EXPERIENCES

Peter Harper, Bettersafe Pest & Weed Management, AustraliaDr. Nimal Chandrasena, GHD Pty Ltd, Australia

Bill Chisholm Aquatic Plant Control, New Zealand

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

WHAT ARE THE MAJOR AQUATIC WEEDS?

WHY CONTROL AQUATIC WEEDS?

• Prevent infection of new water bodies

• Maintain amenity values

• Prevent economic loss, flooding etc.

• Conservation and biodiversity

• Preserve Water quality

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

THE PROBLEM:

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

AQUATIC WEED CONTROL METHODSMethod 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

AQUATIC WEED CONTROL METHODSMethod 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)

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)

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

AQUATIC WEED CONTROL WITH HYDROGEL

o High MW; Polysaccharideo 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 !

HYDROGEL FOR AQUATIC WEED CONTROL

LIVERPOOL, AUSTRALIA, GEORGES RIVER – EGERIA CONTROL WITH DIQUAT GEL

Before After 5000 m2, 15 L Hydrogel mix $1000.00 AU

SUTHERLAND SHIRE, SYDNEY – EGERIA CONTROL WITH DIQUAT GEL

Before After500 m2, 3 L Hydrogel

$ 275 ($ 550/ha)

CABOMBA CONTROL WITH CARFENTRAZONE – GLENBROOK LAGOON SYDNEY, NSW

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. 

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 daysDay 1: 109.8 L, Day 28:45.4 L, Day 56 30.3 L) to achieve 42.1ppb approximate

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