Water hyacinth control & removal

The complete comprehensive guide to water hyacinth control and removal from Australian dams.

Water hyacinth is one of the world’s fastest growing plants

It produces large quantities of seeds that are viable for up to 30 years.

Because of water hyacinth’s ability to quickly reproduce, populations often double in size in just two weeks.

It prefers warmer climates and has thick, glossy leaves that are 10-20 cm across. The hanging roots of the plant feathery and purplish-black in color.

Water Hyacinth can grow in height to as much as 1 meter above the surface of the water. It is supported by an erect stalk that has a single spike of 8-15 flowers.

The flowers are usually lavender and pink in colour and have six petals.

How does this weed affect you?

Water hyacinth is one of the world’s worst aquatic weeds.

It infests rivers, dams, lakes and irrigation channels on every continent except Antarctica.

It devastates aquatic environments and costs billions of dollars every year in control costs and economic losses.

A brief history of water hyacinth

Water hyacinth is a floating perennial plant that is native to the Amazon, and Brazil in particular

Water hyacinth likely generates equal amounts of excitement and dread depending on who is dealing with it, but it is a plant with an interesting history

The modern history of the water hyacinth began on December 16, 1884 at the “World’s Industrial and Cotton Centennial Exposition” in New Orleans, LA.

Among the many amazing wonders on display a never before seen herb was on display in Horticultural Hall.

The herb, Eichornia crassipes, was an aquatic floating plant with dark green thick leaves and a beautiful delicate purple and blue flower with a yellow spot accenting several petals.

This horticultural curiosity of the time quickly escaped the confines of Horticultural Hall and invaded the American waterways of the south.

It was brought to Australia in the 1890s as an ornamental plant.

The first record of water hyacinth in New South Wales (NSW) was in 1895.

In 1897, the government botanist Mr J. H. Maiden noted that it had spread rapidly in the ponds in the Royal Botanic Gardens in Sydney.

At that time, he warned that the plant should be kept away from the northern rivers where it ‘may very rapidly become a serious pest’.

Unfortunately, this warning went unheeded and by the early 1900s it had spread along the east coast of Queensland and the north-eastern regions of NSW.

Water hyacinth description

Water hyacinth ‘Did You Knows?’

• It chokes waterways costing hundreds of millions in removal efforts around the world, greatly affecting local economies and trade routes.
• It chokes out native habitats, ecologies, and species.
• It spreads by wind, floods, birds, boats, and humans.
• It impedes passage of large and small vessels in waterways, by creating impenetrable floating mats.
• It is toxic if ingested by cats, dogs, horses
• The flowers are used to create a tonic for horses that is rubbed into the horses skin
• Given a good steaming or boiling the plant’s flower stalks, buds, and young leaves can be eaten. Water hyacinth is an ingredient in Taiwanese and Javanese cooking. (if ingested uncooked it will cause sever skin irritation.
• The plant is rich in carotene.
• Water hyacinth is used in perfume and cologne products.
• It can be used as organic fertilizer and animal feed.
• It can be processed to make paper, rope, handbags, even furniture.
• It absorbs lead, mercury, and carcinogens when used for remediation purposes.
• Because of its amazing biomass it can be used to create fuels

Water hyacinth germination

Water hyacinth seeds require a number of conditions to germinate.

They include:

• warm temperatures
• high light intensity
• the presence of moist soil or organic matter

Germination mostly occurs in muddy soil and shallow water following periods of fluctuating water levels—where water levels have dropped and the soil has dried out, then been submerged by water again following high rainfall periods.

Water hyacinth has no known direct food value for wildlife and is therefore considered a pest species. However, the hanging roots are often inhabited by invertebrates, which are in turn eaten by other aquatic species (amphibians, reptiles, etc).

Water hyacinth in Australia

Water hyacinth currently occurs along the east coast of Australia from Kiama in NSW to southern Cape York Peninsula in Queensland.

In the early 1900s extensive infestations in the northern coastal rivers of NSW were a major hindrance to river navigation, and infestations still occur in all coastal river catchments, particularly the Macleay, Clarence and Richmond.

Large infestations were present in the Hawkesbury River during the 1990s, and remnant populations are still subject to annual control programs.

In inland NSW, water hyacinth was identified on the Gingham Watercourse near Moree in 1955. By 1976 it had become a major infestation covering 7000 ha.

Despite management and control efforts since then, a significant seed bank still remains across the region, and the area of infestation has moved further west, threatening the Murray–Darling system.

The impacts of water hyacinth

Under the National Weeds Strategy, water hyacinth has been identified as a Weed of National Significance (WONS).

The reason for this classification was due to:

1. The effect on water quality  

Dissolved oxygen levels are reduced beneath the floating mat by decreasing the natural transfer of oxygen from the air at the water surface.

The decreased water oxygen levels results in a changed aquatic habitat, as it reduces fish diversity and impacts on other aquatic flora and fauna

2. Water loss

The amount of water lost from a water body by a water hyacinth infestation can be up to three times larger than the natural evaporation rate of an uncovered water surface.

These high levels are the result of high transpirations rates – water lost through the leaves.

This can have large impacts on water storages with infestations of water hyacinth and river systems that may already be low on water.

3. Agricultural implications

Severe infestations of water hyacinth can prevent access to stock watering points and possibly reduce the amount of quality drinking water available to stock.

4. Loss of bio-diversity

This destruction of native habitat can lead to decreased fish, aquatic invertebrate and water bird populations as the availability of food diminishes.

5. Damage to infrastructure

During flood events, large mats of water hyacinth can move with flood waters.

These large mats can be very heavy, up to 450 tonnes of wet weight per  hectare, which can build up against, and cause damage to, bridges, culverts, roads and fences.

This may obstruct the natural flow of water and possibly increase flood levels, contributing to the loss of infrastructure, livestock and equipment.

Once flood waters subside, large mats of water hyacinth can be left stranded on crops and pastures, destroying the underlying plants, and can be very costly to remove.  

6. Stock danger

Water hyacinth mats can be dangerous for recreational users of water and stock which may become tangled in the roots and stolons of plants if venturing into the water.

Mats may provide a breeding ground for mosquitos which can carry disease such as Ross River virus and Dengue fever.

7. Other specific impacts include:

• blocking irrigation channels and rivers
• restricting livestock access to water
• destroying natural wetlands
• eliminating native aquatic plants
• reducing infiltration of sunlight
• changing the temperature, pH and oxygen levels of water
• reducing gas exchange at the water surface
• altering the habitats of aquatic organisms
• restricting recreational use of waterways
• reducing aesthetic values of waterways
• reducing water quality from decomposing plants
• destroying fences, roads and other infrastructure when large floating rafts become mobile during flood events, and
• destroying pastures and crops when large floating rafts settle over paddocks after flood events

Water hyacinth will rapidly take over an entire waterway. Under favourable conditions it can double its mass every 5 days. 

This enormous reproductive capacity causes annual re-infestation from seed and rapid coverage of previously treated areas, making ongoing control necessary.

How does water hyacinth spread?

Most spread can be attributed to human activity such as the deliberate  planting of water hyacinth in ornamental ponds or dams.

Seeds are the main source of new infestations and are carried in water, mud (e.g. on machinery or boots), by birds and contaminated boating equipment

Unwanted aquarium plants that are discarded into waterways are also a major form of spread.

Removal of water hyacinth in your dam

Removing water hyacinth is no easy feat, but it’s not impossible.  

There are several ways you can go about removal. Some take the manual route and physically remove the weeds via raking or skimming them off the water surface.

However if you have a particularly large water hyacinth problem where they have heavily overtaken your pond or lake, physical control may be too labour intensive, costly and time consuming to carry out.

There is a 4 step process for killing, removing and managing large water hyacinth infestation in dams.

1. Chemical spraying

Liquid herbicides are a great solution because they attack weed growth in shallow water on or above the dams surface and can be spread evenly with a power sprayer.

Treatments with herbicides should be carried out early in the growing season (generally in spring).

Spraying an entire heavy infestation can cause the weed mat to sink and rot resulting in deoxygenation of the water, potentially killing fish.

This can be avoided by spraying one third of the infestation at a time, or by physically removing as much of the weed as possible prior to spraying.

In NSW, a number of herbicides are registered for the control of water hyacinth.

Metsulfuron-methyl 600 g/kg (Brush-off®)

Comments: May only be applied in enclosed water bodies, and not within 400 m of potable water supply uptakes.

WARNING: very toxic to aquatic plants and algae. Apply a maximum of 3 applications per year at minimum intervals of 90 days.

Withholding period: Nil (recommended not to graze for 7 days before treatment and for 7 days after treatment to allow adequate chemical uptake in target weeds).

Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors)
Resistance risk: High

2,4-D 300 g/L (Affray 300®)

Rate: 1.0 L in 200 L of water

Comments: Avoid causing submersion of sprayed plants.

Withholding period: 7 days.

Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)

Resistance risk: Moderate

Amitrole 250 g/L (Amitrole T® )

Rate: 280 mL to 100 L of water

Comments: Apply prior to flowering.

Withholding period: Nil.

Herbicide group: Q, Bleachers: Inhibitors of carotenoid biosynthesis unknown target

Resistance risk: Moderate

Diquat 200 g/L (Reglone®)

Rate: 400 mL per 100 L of water

Comments: Add Agral 600 wetter; use clean water for best results. Observe withholding period.

Withholding period: 1 day in pasture, 10 days in treated water.

Herbicide group: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)

Resistance risk: Moderate

Glyphosate 360 g/L (Only products registered for aquatic use)

Rate: 1.0–1.3 L in 100 L of water

Comments: Apply when actively growing, at or beyond the early bloom stage. Use higher rate on dense infestations.

Withholding period: Nil.

Herbicide group: M, Inhibitors of EPSP synthase

Resistance risk: Moderate

Application of herbicides

The most commonly used technique for applying herbicides to water hyacinth is high volume spraying with power sprays either from a boat or from the banks.

In some situations large infestations have been aerially sprayed.

The potent concentration of active ingredients in these herbicides damages plant’s cellular members and inhibits plant’s ability to photosynthesize.

The herbicides are quickly absorbed by the plant and begin working on contact. In or out of water, the herbicides very strongly bind to foliage and will not rinse off.

The best results are achieved when applied to well developed foliage, but before growth becomes too dense or weeds flower.

Wilting and loss of foliage occur quite rapidly.

Turbid water or mud covered foliage will reduce the herbicides absorption and effectiveness.

For difficult to control weeds, you can add Cutrine-Plus Liquid to boost effectiveness.

Ratings of effectiveness of active ingredients for water hyacinth treatment:

• Bispyribac (Rated: Excellent)
• Diquat (Rated: Excellent)
• Glyphosate (Rated: Good)
• Imazamox (Rated: Excellent)
• Imazapyr (Rated: Excellent)
• Penoxsulam (Rated: Excellent)
• Triclopyr (Rated: Excellent)
• 2,4-D (Rated: Excellent)

These rating are based upon the U.S. Army Corps of Engineers aquatic herbicide trials.

Precautions

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material.

Oxygen depletion can kill fish in the pond. If the pond is heavily infested with weeds, it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

Application considerations

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

2. Physical removal.

After the weed mass starts to wilt and die, control attempts should concentrated on removing plants from the water and dumping the accumulated mass on land to die.

Mechanical removing of plants from farm dams and drains is an effective form of controlling water hyacinth, but only when the rate of removal is faster than the rate of regrowth.

There are instances where mechanical harvesting of large infestations has been effective, although costly. As a guide, it takes between 600 and 900 hours to harvest one hectare of dense water hyacinth – which should be undertaken prior to flowering and seed set.

Fifty million tonnes of water hyacinth are removed from the White Nile annually, and the Panama Canal is kept clear of the weed by mechanical harvesting.

Mechanical removal of the sprayed weed mat is necessary to prevent re-flowering.

Ongoing monitoring and follow-up treatments will still be required, otherwise efforts will be counterproductive and the infestation will re-establish.

3. Water levels

Manipulating water levels will control water hyacinth

When dam water levels are less than 1m due to silting, a mass germination of dormant seeds occurs.

Where water levels can be manipulated within a body of water, raising the water level can be used as a tool for managing the seed bank.

Deep water levels in the dam stops seed germination and the re-establishment of water hyacinth.

This option should only be considered if supplemented with follow-up treatment of emergent seedlings with a registered herbicide prior to flowering and seed-set.

4. Biological control

Four insects from South America have been released by CSIRO since 1975 and are well established across NSW.

There are two weevil species, Neochetina eichhorniae and Neochetina bruchi, and two moth species, Niphograpta albiguttalis and Xubida infusellus.

The weevil, Neochetina eichhorniae, has been successful in destroying large water hyacinth infestations in tropical northern areas of Australia. The adult is black, 5 mm long, and feeds on leaves, making small scars.

Eggs are laid in the bulbous leaf stalks and the larvae tunnel through the plant tissue, which is then attacked by bacteria and fungi. This causes the plant to become waterlogged and death can occur under heavy attack. These weevils are inactive during winter.

The weevil, Neochetina bruchi, is more active through the winter and is now well established from northern Queensland to Sydney, although both weevils are much less effective in subtropical and cooler areas of NSW.

The moth, Niphograpta albiguttalis, is well established in northern NSW and Queensland. Its larvae tunnel into the leaf stalks and buds, as do the larvae of Xubida infusellus. Both species are very damaging to young plants and luxuriant weed growth but their impact is often temporary and patchy.

Unfortunately biological control cannot be solely relied upon for effective control of water hyacinth in NSW. It will provide some reduction in flowering and growth rates of the plant and occasionally mat sinkage has occurred as a result of insect damage.

You should view biocontrol as a useful addition to the other available control techniques. It is possible that some infestations exist which do not have biological control agents present.

Water hyacinth legal requirements

References:

• NSW Department of Primary Industries 
• Lake restoration
• NSW DPI : Weed of national significance
• Water Hyacinth control 
• Questions and answers about removing water hyacinth plants 
• Hyacinth Control Modules