Crofton weed (Ageratina adenophora)

Introduction:

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 (Ageratina adenophora), 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 around 1900, it has become widespread in Queensland coastal areas and 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 39 local government areas of coastal New South Wales, 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 an erect, perennial shrub with numerous chocolate-brown woody stems emanating from an underground crown and reaching a height of 1–2 m. It has broad, slightly crinkled, trowel-shaped, toothed leaves with chocolate-coloured petioles. It produces white flowers in spring. Crofton weed and mistflower are sometimes mistaken for each other. Table 1 distinguishes between the two species.

Why it is a weed:

It spreads rapidly:

Mature Crofton weed plants can produce between 10 000 and 100 000 seeds per year. Seeds are very light (25 000 seeds/g) and are windborne over long distances to invade previously noninfested areas. The seeds require light to stimulate germination so that 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

• fencelines.

Once established, seedlings tolerate shade and grow rapidly. In this way, small infestations of Crofton weed rapidly increase in size unless controlled. Crofton weed reduces the ecological value of bush land, lowers crop yields and reduces the carrying capacity of grazing land. The weed spread rapidly during the 1940s and 1950s and it was reported that in some areas dairy farmers and banana growers abandoned their holdings! The area of Crofton weed infestation has now been substantially reduced through control strategies.

Control:

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.

Mechanical control:

Small areas of scattered plants can be dug out with a mattock. Crowns must be removed to prevent regrowth. Slashing is often used to control heavy infestations on

accessible land. Regular slashing will reduce flowering and seedset, thus reducing spread by seeds. It will also reduce the vigour and density of Crofton weed infestations and, combined with competitive pastures, will eventually bring them under control. The slashed and dried plant, however, is still attractive and toxic to horses. Take care to keep horses away until the plant has been completely removed from the paddock.

Chemical control:

In New South Wales, several chemicals are registered for the control of Crofton weed (see Noxious and Environmental Weed Control Handbook and Weed Control in Lucerne & Pastures). For further advice on herbicides, consult the nearest NSW Agriculture office or your shire council weeds officer. Chemical treatment appears to work most effectively during late summer and autumn. When spraying Crofton weed with herbicides it is important to ensure that spray does not drift onto desirable plants and to maintain operator safety. Instructions on operator safety and application methods are on the container labels: you must read and understand these before using the chemical. A combination of slashing and chemical application is often used to eradicate Crofton weed. After slashing, the weed is allowed to regrow from the crown to a height of 15–40 cm and then sprayed with herbicide. Combined with the introduction of competitive species, this strategy restores the productivity of infested land.

Grazing management:

Well-managed, competitive pastures are important in preventing weed invasion and this principle also applies to Crofton weed. Dense pasture swards suppress seed germination and livestock eat young seedlings with the balance of their feed. Therefore, fewer plants grow to maturity. Goats are known to eat Crofton weed. The degree of weed control by goats depends on the stocking rate, weed density and the availability of other suitable feed. Using goats to help control widespread infestations may be worth considering, although some knowledge of goat husbandry and fencing is necessary. The same group of goats should be used for only one or two seasons to avoid risk of chronic health problems.

Sourced From: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0010/155962/crofton-weed.pdf