Pest Plants

What Is a Pest Plant?

Pest plants are plants of any sort -- whether "weed" or cultivated, native or introduced -- growing where they cause problems. Many are aggressive in their growth and capable of completely taking over waterways, areas of bush, farmland or garden they spread into. They not only smother existing plants and even trees, but damage the habitat of animals native to the bushland or water they invade. Many of the plants declared as weeds in Queensland are species which were introduced years ago for use in home gardens, but which have spread, through natural means or dumping clippings, into bushland and waterways. Any plant officially declared a weed is considered a serious pest, and control is enforced by law (Rural Lands Protection Act 1985).
 
The information below describes several pest plants of real threat to Bulimba Creek Catchment and what you can do to help control their spread. Information extracted from:
        Grow Habitat, Not Weeds -- Brisbane City Council poster
        DNR Pest Facts brochures
        Suburban Weeds, 3rd edition, 1996, by Kleinschmidt, Holland and Simpson. Dept. of Primary Industries Qld.
 
Contact the Department of Natural Resources on 1800 803 788 or (07) 3227-7111 for help identifying species and for detailed information on their control.

How Can Pest Plants Be Safely Controlled?

Complete Removal
Use this with plants which regrow from bulbs, tubers, runners, stem pieces or other parts. Making certain no parts remain to regrow or escape back into waterways may mean drying and burning the removed plants.
 
Stem Scraping
Scrape the sides of the main stem to expose the growing layer, and within 15 seconds apply the chemical glyphosate to the scraped areas.
 
Cut and Swab
Cut off the above-ground stems or trunk and apply glyphosate within 15 seconds on the cut surface. Suited for vines without aerial tubers, and for woody plants.
 
Stem Injection
Suited to trees. Make horizontal cuts around the trunk and into the growing layer, then apply glyphosate within 15 seconds.
 
Herbicide Spraying
Suited to large, smothering infestations with plenty of leaf surface. Use according to manufacturer and Department of Natural Resources guidelines.
 
Biological Control
Available for many pest species, often used in conjunction with other methods until the insects are established. Contact Department of Natural Resources for information and supplies.

Morning Glory Ipomoea indica

Description
Rampant big-leaved vine with attractive blue-purple flowers. Seed is dispersed by wind. Perenial, flowering in autumn and winter.
 
Why It's a Problem
This highly invasive weed can smother and destroy native vegetation and animal habitats. It has spread from N. Queensland to the NSW border in disturbed rainforests, along waterways and roadsides, and in neglected urban and rural blocks.
 
Control
Cut vines close to the ground and apply herbicide immediately to cut surfaces.

Para Grass Brachiaria mutica

Description
Exotic grass now present on most stream banks around suburban Brisbane. Loose tufts of broad-bladed grass over 1 m tall, with densely hairy stem nodes.
 
Why It's a Problem
Para grass rapidly grows along tropical stream banks to crowd out native grasses and other vegetation.
 
Control
Spot spraying with glyphosate, then replant native rainforest trees along stream banks to shade out para grass.

Salvinia species

Description
Salvinia species are free floating aquatic ferns with small spongy green leaves and long hair-like trailing roots. Salvinia reproduces vegetatively from plant fragments and has its fastest growth in summer, with plants doubling in volume in a few days during hot weather.
 
Why It's a Problem
Salvinia is a rapid growing plant which forms dense mats able to smother waterways and dams. Children and livestock may drown if they become entangled in the roots of such mats. Like other mat-forming pest aquatic plants, it encourages mosquito breeding. The mats block sunlight and reduce oxygenation in the water they cover, and the huge volume of decaying plant material caused by the death of other water plants smothered by Salvinia mats pollutes the water.
 
Control
Salvinia is a declared pest plant under the Rural Lands Protection Act 1985. Hand or mechanical removal can be used in small areas of infestation. After removal and drying, the plants should be burned so later rains don't reintroduce fragments to the waterway. Biological control using an introduced weevil species is effective, especially in warm areas. Selective herbicide spraying can be used initially while the weevils are becoming established (a 1 to 3 year process in warm regions, longer in cool areas). Contact the Department of Natural Resources on 1800 803 788 for further information.

Singapore Daisy Wedelia trilobata

Description
Native to Central America, this fast-growing creeper with bright yellow flowers was introduced to Australia in the 1970s. It prefers sandy, well-drained soil and thrives in coastal areas. A perennial whose seed is dispersed by the wind, it also regrows from runners and stem cuttings.
 
Why It's a Problem
It can form a dense mat of foliage capable of completely smothering native seedlings. It invades coastal sand dunes as well as roadsides and rainforest fringe, readily spreads from gardens, and can easily grow from dumped clippings.
 
Control
Control is difficult, but can be successfully done by hand weeding. Be sure to collect all removed plant parts in plastic bags, or dry and burn to prevent sections from regrowing.

Water Hyacinth Eichornia crassipes

Description
Water hyacinth was introduced from Brazil into Australia as an ornamental plant. It is a floating aquatic weed with large, dark green rounded leaves and a fibrous tangle of roots. It grows both from seed and through daughter plants developing from stems.
 
Why It's a Problem
Water hyacinth grows densely and rapidly and can destroy wetlands and waterways, with some infestations doubling in size every week. Native water plants and fish are deprived of light and oxygen, and the dense mats encourage mosquito breeding. The tangle of roots can endanger livestock or people who become caught in them. It is a declared plant under the Rural Lands Protection Act 1985.
 
Control
Physical removal works for small infestations -- be sure to do this before flowering and seed setting in October. Dry and burn the removed weed. Biological control is also possible, and is especially effective on large areas of water hyacinth. This uses introduced weevil and moth species to cover much of the year's growth period. Selective spraying of herbicide can control or reduce infestations enought to allow mechanical or biological control to handle the rest. Contact the Department of Natural Resources on 1800 803 788 for information on biological control and herbicide use for water hyacinth.

Water Lettuce Pistia stratiotes

Description
Introduced from Asia as an aquarium and pond plant, water lettuce is a floating aquatic weed with a lettuce-like head of pale green, fan-shaped leaves. The leaves are covered with hairs which trap air and help the plant stay afloat. Its long trailing roots can reach 80 cm. It spreads by both seeds, which germinate in late spring, and by growth from stolons (branches able to strike roots).
 
Why It's a Problem
Water lettuce is rapid-growing in warm regions. It forms dense mats cabable of smothering dams, canals and even flowing rivers, slowing water flow and increasing water loss through transpiration. The calmer water conditions encoueage mosquitos breeding. Water lettuce is a declared plant in Queensland under the Rural Lands Protection Act 1985.
 
Control
Water lettuce is best controlled using a combination of methods. Mechanical control, removal and drying the collected weed is practical in only small infestations. Biological control is possible using two weevil species and is particularly effective in dams. Because it can take some years to achieve effective numbers of the weevils, control using other methods should be used as well. Autumn application of selective herbicides is effective for large infestations and can be used to reduce the size of the area affected enough to allow weevils to control the remainder. Contact the Department of Natural Resources to obtain the weevils and for guidance on herbicide use.