Quick Facts

Quick facts

• Mistflower (Ageratina riparia) is a low-growing, scrambling perennial herb or subshrub
• It is an aggressive weed which invades pastures and displaces native vegetation.
• Mistflower is found along shaded riverbanks in humid subtropical and tropical rainforests.
• Mistflower is deemed to have no feed value for stock.
• To date there seems to be no particularly effective biological control agent for Mistflower.

What Does It Look Like?

What is it?

Mistflower (Ageratina riparia) is a low-growing, scrambling perennial herb or subshrub with purplish, cylindrical stems with a sparse cover of fine hairs. It usually grows 40-60 cm tall but is sometimes to 1 m high. It has a short thick rootstock. The leaves are arranged opposite to each other on the stem. They are green, narrowly-ovate (egg-shaped and attached to the leaf stalk at the wider end) or lanceolate (elongate and narrowing at the tip), 3-13 cm long and 1-4 cm wide with toothed margins, especially in the upper half of the leaf.

The white flowers are about 5 mm long and grouped together in heads which are in turn arranged in terminal clusters at the end of long branches. The small flower-heads do not have any obvious 'petals' and consist of several tiny flowers.  Several of these flower-heads are clustered together at the tips of the branches. Flowering occurs from late winter through to late spring, but is most abundant during mid-spring (Biosecurity Queensland 2016).

Fruit is dry slightly-curved seeds which are dark brown to black, 1-2 mm long, and have 4 or 5 hairy ridges which run lengthwise. They are topped with a ring of rough hairs (the pappus) which are 3-4 mm long (Parsons & Cuthbertson 2001; Navie 2004; Weeds Australia undated).

For further information and assistance with identification of Mistflower contact the herbarium in your state or territory.

Flower colour

White

Growth form (weed type/habit)

Shrub, Herb

Where it currently grows? Preferred habitat

Mistflower is found along shaded riverbanks in humid subtropical and tropical rainforests. There has been considerable invasion by this species of steep hillsides and roadsides in wetter plateau areas, with the plant favouring south-facing slopes (Parsons & Cuthbertson 2001; Land Protection 2006).

Are there similar species?

Mistflower is only likely to be confused with the related Crofton Weed (Ageratina adenophora). However, Crofton Weed is erect and often 1-2 m tall, not a creeping or scrambling herb. The young stems of Crofton Weed are densely covered in sticky glandular hairs, unlike those of Mistflower, and the toothed leaves of Crofton weed are broader and trowel-shaped (Navie 2004).

Why Is It A Weed?

What are its impacts?

Mistflower is a significant environmental weed in New South Wales and Queensland.

Agriculture: In south-eastern Queensland it spreads into pastures and reduces the carrying capacity significantly. Abandoned banana plantations are a stronghold for Mistflower. Mistflower is deemed to have no feed value and there are no field reports of animals dying from the consumption of this plant. However, in laboratory tests, alcohol extracts of this plant have killed sheep while horses fed the plant have developed palpable nodules in the lungs (Parsons & Cuthbertson 2001; Land Protection 2006). It can spread into wetter pastures, significantly reducing their carrying capacity. It may also restrict the movement of livestock and farm machinery (Queensland Biosecurity 2016).

Native ecosystems: Mistflower spreads into bushland displacing native vegetation. It will quickly invade disturbed areas on frost-free slopes and dominate riverine groundcover habitats, excluding many native species and the native animals which are reliant upon the native plants. It is especially invasive in gullies and riparian habitats and is often reported to dominate the groundcover vegetation along waterways. It is shade tolerant and can almost totally exclude native plants in these areas, an may even displace many of the animals which were reliant upon those plants.

Several rare and endangered native plants are also thought to be threatened by mistflower (Ageratina riparia) in New South Wales. The ravine orchid (Sarcochilus fitzgeraldii), which is restricted to few sites in wet sclerophyll forests and rainforest ecotones in north-eastern New South Wales, and Hartman's sarcochilus (Sarcochilus hartmannii), an epiphytic orchid from south-eastern Queensland and north-eastern New South Wales, are two important examples. The endangered Border Ranges daisy (Brachyscome ascendens) and the vulnerable giant spear lily (Doryanthes palmeri) are two more species from this region that are known to be treatened by mistflower (Ageratina riparia). A dense groundcover of this weed has been reported in sites where giant spear lily (Doryanthes palmeri) grows in northern New South Wales, and its faster growth rate is likely to enable it to out-compete the native plant in most situations. At Mount Cordeaux in south-eastern Queensland, where mistflower (Ageratina riparia) is spreading down a whole cliff-face, it appears to be displacing giant spear lily (Doryanthes palmer) (Biosecurity Queensland 2016).

Further south, the Illawarra irene (Irenepharsus trypherus) is also threatened by weeds, and mistflower (Ageratina riparia) has invaded some of the locations where this superficially similar rare native species still grows. Weed invasion is also regarded as a major threat to the integrity of Illawarra sub-tropical rainforest in the Sydney Basin bioregion, and one of the invasive exotic species that is threatening this ecological community is mistflower (Biosecurity Queensland 2016).

How does it spread?

The spread of Mistflower is mainly by seed, which is adapted for movement in wind and water. Some spread also occurs when seed are present as impurities in agricultural produce, in sand and gravel used in roadworks, and in mud sticking to animals, machinery, other vehicles, clothing and footwear. Existing colonies increase in size and abundance by layering, forming a mat of interwoven stems (Parsons & Cuthbertson 2001).

What is its history in Australia?

Mistflower appears that to have been introduced to Australia in about 1875. It is listed as growing in the Botanic Gardens of Adelaide in 1878, in Melbourne in 1888, Sydney in 1895 and Brisbane in 1901, but it was not until it was introduced to northern New South Wales that it began to naturalise. It was introduced to the north coast of New South Wales as an ornamental plant during the 1920s and within a few years began to colonise newly cleared land. The first record for Queensland, from Springbrook, was in 1930 (Auld & Martin 1975; Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

It is recommended to  not overgraze pasture in the first place to help prevent the establishment of Mistflower.

Chemical control: Aerial application of fertiliser in steep country produces thick pasture, which will provide strong competition for mistflower. Re-establishment of pasture, where necessary, after herbicidal control is recommended to restrict seedling regeneration and prevent erosion. Newly established pastures preferably should not be grazed until they have seeded. (DAF Queensland 2020). Any regrowth of mistflower should be spot sprayed. Mistflower is resistant to some herbicides and for long-term control herbicide treatment may need to be repeated (Parsons & Cuthbertson 2001; Land Protection 2006).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .

Non-chemical control: Mistflower can be controlled mechanically through hoeing, grubbing and burning but it is essential that replacement pasture plants or native plants be sown on the treated areas to prevent re-establishment of the weed. Mechanical removal is not always practical and herbicides may be used.

Mistflower has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. The Gall-forming Fly Procecidochares alani was introduced to Australia in 1987 as a biocontrol agent for Mistflower but with limited success as it is parasitized by native wasps. Other biological agents have been useful control agents in Hawaii and New Zealand but do not appear to have been released in Australia (Zancola et al. 2000).

Red-necked Pademelons in disturbed and regenerating rainforests on the Springbook plateau in south-eastern Queensland browse extensively on Mistflower. This browsing and physical damage breaks up the broad stands of Mistflower and creates the potential for native species to re-establish (Zancola et al. 2000).

Does it have a biological control agent?

YES

When does it grow? (lifecycle/growth calendar)

Seeds of Mistflower germinate in late spring-summer. Budding occurs around July to August, with full flowering occurring in the period August to October. After flowering the top of the plant dies off and reshoots from the base. Mature plants produce between 10 000 and 100 000 seeds annually. The seeds can germinate immediately, but only in light. Leachates from the leaves and plant litter have an allelopathic effect on other plants (that is, they inhibit the establishment and/or growth of other plants) (Parsons & Cuthbertson 2001; Land Protection 2006).

Where Is It Found?

Which states and territories is it found?

NSW, QLD

What areas within states and territories is it found?

Mistflower is generally present in coastal and near-coastal areas of much of New South Wales and southern Queensland, being particularly abundant in the forested coastal regions near the Queensland/New South Wales border. It is also present in parts of central and northern Queensland and as far south as Nowra on the New South Wales south coast. Also naturalised on Norfolk Island and possibly sparingly naturalised in south-western Western Australia. as well as south-western Western Australia (Navie 2004, Biosecurity Queensland 2016).

It is naturalised in parts of southern Africa, Madagascar, La Réunion, the Canary Islands, India, Indonesia, Papua New Guinea, Southeast Asia, Hawaii, some pacific islands, and New Zealand (Parsons & Cuthbertson 2001; Navie 2004; PIER 2007; Weeds Australia undated).

Where does it originate?

Mistflower is a native of Central America (Mexico) and South America.

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, NT, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Ageratina riparia

Other scientific names (synonyms)?

• Eupatorium riparium Regel
• Eupatorium rivularum C.T.White & W.D.Francis 

Does it have other known common name(s)?

Mist Flower, Creeping Croftonweed, River Eupatorium, Spreading Mistflower