Crofton weed is a rapid-spreading weed that has become a nuisance in many areas along the eastern coast of Australia.

It is particularly invasive on cleared land that is not grazed, such as public reserves, and causes particular problems for horse owners.

A member of the Asteraceae or daisy family, Crofton weed is a native of Mexico. It is present as a weed in India, Sri Lanka, the Canary Islands, Jamaica, mainland United States, Hawaii, Fiji, New Zealand and Australia.

Since its escape from ornamental cultivation in Australia about 1900, it has become widespread in Queensland coastal areas, on the New South Wales North Coast, and as far south as Wollongong. Isolated infestations also occur on the northern and central tablelands.

Crofton weed is a declared noxious plant in 35 local government areas of coastal NSW, most lying between Gosford and the Queensland border.

The weed has been present in the Sydney region for more than 30 years and has spread rapidly in this area since the early 1970s. It is now a problem weed, especially on small farms where horses are kept.

Crofton weed and its close relative, mistflower (A. riparia), infest large areas of the coast, especially steep, well-drained land where annual rainfall is more than 1500 mm and where there are few or no frosts.

Description

Crofton weed is a bushy, leafy perennial, which grows to about two metres tall. Parts of the plant have a strong aromatic smell when bruised.

It has a tap root and an extensive fibrous root system.

The many stems are purplish in colour.

Leaves are soft, thin and shaped like a triangle, with a toothed edge and conspicuous veins. They have a dark green upper surface, are lighter underneath and may be slightly hairy. They are 4-12 cm long and 3-9 cm wide.

Crofton weed has clusters of white, tubular flowers, which are produced in profusion in early spring.

Seed is dispersed over long distances by wind and water and is also moved by vehicles, machinery and in clothing, soil and stock feed.

Crofton weed forms dense stands and prefers moist, nutrient, rich soil. Poisonous to horses, it spreads rapidly and is found on abandoned land.

Mature plants can produce between 10,000 and 100,000 seeds a year. Seeds are very light (25,000 seeds/g) and are windborne over long distances to invade previously non-infested areas.

The seeds require light to stimulate germination, so invasion commonly takes place on bare, disturbed sites and only rarely on heavily vegetated areas.

Places where Crofton weed is commonly found include: land cleared but not revegetated with pasture, roadsides and waste areas, ungrazed small holdings, State forests, National parks, abandoned banana plantations and fencelines.

Crofton weed reduces the ecological value of bush land, lowers crop yields and reduces the carrying capacity of grazing land.

Horses may preferentially graze the plant even when ample feed is available. Access to Crofton weed for as little as eight weeks can cause sickness.

Crofton weed can be controlled using a combination of methods, in conjunction with pasture and grazing management practices, aimed at creating an unfavourable environment for weed invasion.