Koster’s curse is a declared Class 1 Noxious Weed in NSW and is the target of a national eradication program.

It is a highly invasive shrub, growing up to five metres tall and has the potential to spread rapidly over many parts of Australia.

Koster’s curse forms dense thickets, which can smother pasture and native vegetation in a similar manner to lantana.

It is quick-growing and could cause major problems for primary industries.

It invades disturbed areas including the edges of clearings and stream-banks, along fence lines, paths and roadways.

The weed prefers humid tropical lowlands and therefore could spread to humid coastal sites in the Northern Territory, over much of north-east Queensland and down the coast to Northern NSW.

The most common method of dispersal is by birds and mammals that eat the berries, but the fruit may also be spread by water and human intervention, such as in potting material, or mud on machinery or vehicles.

Koster’s curse is the target of a national, cost-shared eradication program managed by Biosecurity Queensland (a business group of the Department of Primary Industries and Fisheries) with financial support from other states and the Federal Government.

Appearance

It is a bushy perennial, evergreen shrub, which reaches its maximum height in moist, shady conditions. In harsh growing conditions it may appear as a weak and straggly small shrub.

Leaves are elliptical with toothed margins, a wrinkled, papery surface texture and five conspicuous longitudinal veins. Stiff, reddish brown hairs cover the stems and leaves. Leaves are normally 8-10cm long, oppositely arranged and hairier on the under surface.

Koster’s curse produces clusters of 6-20 small white flowers in the leaf forks.

The flowers are 1-1.5cm in diameter and produce red-purple to blue-black berries, 4-5mm in diameter. The berries are also hairy and turn dark purple on maturity.

Flowering and fruiting appears to occur all year, except at dry times.

Reproduction is by seed and each Koster’s curse plant has the potential to produce 500 berries a year, with each berry containing up to 900 seeds.

The seed can persist in the soil for at least four years. Seedling establishment is also very successful.

The plant can also reproduce vegetatively.

Plants tolerate a range of environmental conditions and reach full maturity in six months.

Koster’s curse has a wide native range extending from southern Mexico through Costa Rica to northern Argentina and the West Indies.

It is a serious weed on several tropical oceanic islands such as Malaysia, Singapore, Brunei, Indonesia, Papua New Guinea, Fiji, Seychelles, Samoa, and Hawaii.

It was first found in Australia at a nursery near Julatten, in Mareeba Shire, North Queensland, in 2001.

It is suspected to have entered as a contaminant of packaging material. No other infestations have been found.