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Mistflower

Mistflower (L) & Crofton (R)

mistflower leaves

Mistflower fl & fr

Mistflower seed

Crofton weed flowers

Crofton leaves

Indian weed, native

Stinging nettle



Family

Asteraceae (daisy family)

Status

Mistflower (Ageratina riparia) is declared noxious in Class 4 in Shoalhaven LGA, as is the similar Crofton weed (Ageratina adenophora). The latter is also listed in class 4 in Bega Valley LCA.

Description

Mistflower is a branching perennial herb about 1m high, although often sprawling out over water along creek edges. Leaves are diamond or lozenge shaped, in opposite pairs, and leaf margins are finely toothed. Flowers are small, fluffy and white, in branched terminal clusters. The first photo shows mistflower and the very similar Crofton weed growing together.

Preferred habitat and impacts

A weed of moist, warm situations such as creek banks, road verges on moist slopes, storm water drains. Mostly confined to the northern coastal part of the region, north from about Nowra. Much more common in northern NSW, where it also invades pasture. Sometimes used as a garden plant, and therefore naturalised around some towns in southern Australia.

Mistflower forms dense stands in moist sites, choking out native vegetation. If it moves into run-down pasture stock carrying capacity can be reduced. Seedlings are not very competitive in vigorous pasture.  Mistflower has been shown to be toxic to some stock in laboratory trials.

Dispersal

The tiny black or dark brown seed has a "parachute" of fine hairs, and is spread by wind and water, and in contaminated soil on vehicles and machinery, or on clothing. Broken off pieces may take root, and local spread occurs when branches trailing over the ground take root.

Look-alikes

Crofton weed has a very similar habit and flowers but leaves are triangular to trowel-shaped, tapering abruptly to the leaf stalk, 5-8 cm long, on long stalks (see first photo, where Crofton weed is on the right).

The native herb "Indian weed" (Sigesbeckia orientalis) has a similar habit and leaf shape, but leaves are more arrowhead shaped, flowers are tiny and yellow, and enclosed by very sticky bracts. Native stinging nettle (Urtica incisa) has similar leaves to mistflower, in opposite pairs, but it has inconspicuous flowers in long narrow spikes, and is covered in long visible stinging hairs. It often grows in similar shady areas near creeks.

Control

Hand-pull or dig, or spray with non-selective or selective woody weed herbicide, when the plant is actively growing, but before flowering occurs. Monitor and control any regrowth. A biological control for mistflower was introduced into southern NSW in 2011 and is proving quite effective in defoliating the plants, although they may subsequently recover. Called the white smut fungus (Entyloma ageratinae) it causes brwon patches on the upper leaf surface and edges and white fluffy fungal growth can be seen on the lower leaf surface. Unfortunately this fungus does not appear to affect Crofton weed.