Above Image: Blue Morning Glory, Bruce Highway - Courtesy of Noosa District Landcare

Weeds…why are some people really passionate about picking on these sometimes beautiful plants? Very basically, a “weed” is a plant growing where it is not wanted.  To me, a plant becomes a serious weed when it affects the balance in nature. It behaves much like the school bully, outcompeting and upsetting its mates. At the extreme end of this a weed can become a monoculture not allowing anything else to grow at all. I will give you some examples of this later…

Weeds can have negative effects on environmental, cultural, social or economic values.

Environmental values can be altered by invasion and replacement of the native plant community, which can alter habitat, change nutrient cycles, water cycles and quality, and also change fire regimes.

Cultural impacts include reduction in traditional food sources for indigenous Australians, and the creation of physical barriers to the land.[examples include Lantana -Lantana camara var. camara] and Mimosa [Mimosa pigra].

Social or recreational values can also be severely impacted.  Fishing, camping and bushwalking can all be affected. Aquatic weeds drastically change the water body with impacts on boating, fishing and water activities.

Economic impacts are hard to quantify, but are generally recognised to cost Australian agriculture around 4 billion dollars annually.  Some of these impacts include the cost of weed treatment, stock illness [through toxicity], increased transpiration reducing the amount of water available to stock, contamination of agricultural crops, and even by providing a refuge for feral animals.

Above Image: Water hyacinth, Mary River Barrage - Courtesy of Noosa District Landcare

Weeds and the law

In Queensland, pest plants can be declared under the Land Protection Act -2002. This legislation lists three categories of pest plants.

Class 1 pest plants are ones that has the potential to become a serious pest. The objective is to prevent the importation, possession and sale of these species. It is a serious offence to introduce, keep or sell Class 1 pest plants [fines of up to $60,000 apply. In our region examples of Class 1 pest plants include Alligator weed [Alternanthera philoxeroides], and Glush weed [Hygrophila costata].

Class 2 pest plants are ones that have already established but their impact is so serious that we need to control and avoid further spread of these plants. Landowners have a legal responsibility to keep their land free of Class 2 pest plants. Examples include Groundsel bush [Baccharis halimifolia], Olive hymenachne [Hymenachne amplexicaulis cv. Olive] and Salvinia [Salvinia molesta]. These are the plants that council officers can issue a notice to landowners to control on their land. Fines of up to $30,000 apply for transporting or selling these species.

Class 3 pest plants are often called Environmental weeds. They are commonly established and whilst landowners do not have to control them [unless they are adjacent to an environmentally sensitive area such as a National Park], it is an offence to sell or introduce them.  Examples of Class 3 pest plants include Dutchman’s pipe [Aristolochia elegans], Camphor laurel [Cinnamomum camphora], and Singapore daisy [Sphagneticola trilobata]. Fines of up to $15,000 apply to these species for introduction or sale.

These are just the declared species; many more species have serious impacts on our environment. They may be Ok in the garden, but they often don’t stay behind the fence. Indeed, most of our weed species are garden plants that have ‘jumped the fence’. Birds, wind and water often spread the seed where, once established, they take over their environment. Some of the exotic plant species have disastrous effects on our native fauna.

an example - Effect of weeds on the Richmond Butterfly

Take the Richmond birdwing butterfly for instance. This magnificent butterfly was once common in our region and is now listed as vulnerable. Apart from habitat loss, one of the main enemies of this butterfly is the exotic vine Dutchman’s pipe.  The natural food plant of this butterfly is the Richmond birdwing butterfly vine [not surprisingly!] -Pararistolochia praevenosa. The Dutchman’s pipe is a related species -Aristolochia elegans and is a native to Brazil. It attracts the butterfly to lay her eggs on the plant which is toxic to the larvae….result = death to the larvae, and serious implications for the continuation of this beautiful butterfly.

an example - Camphor laurel

Camphor laurel is another good example. Around here they are common. Next time you see one; have a look to see if any of the leaves are chewed. Not likely, as the plant contains toxins that can kill many of our insects. This toxin contained in the leaves drops into our waterways and can kill or reduce the numbers of macroinvertabrates [the bugs that aquatic animals feed on].

So, what do we do about weeds?

• Learn about the species that you should not be planting.
• Plant local native species where possible.
• Jump on a weeds website and see if you can recognise them in your garden.
• Join a local Catchment, Landcare or other environmental group and learn a bit about them. It is important to know the plant before you go around killing them…you may be killing the host plant for a beautiful butterfly!

Noosa's Native Plants: www.noosanativeplants.com.au
Noosa Landcare: www.noosalandcare.org

Not all aquatic plants are evil! Look at this beauty…Ottelia ovalifolia- Swamp lily, a native plant in all States of Australia - Courtesy of Noosa District Landcare