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Lantana is regarded as one of the worst weeds in Australia because of its level of invasiveness, it's potential for spread, and economic and environmental impacts.
It forms very dense, impenetrable thickets that can completely take over native bushland and pastures throughout the east coast of Australia. It competes for resources with, and reduces the productivity of, pastures and also forestry plantations. It adds fuel to fires, and is toxic to stock.
It is an extremely serious threat to biodiversity in several World Heritage-listed areas including the Wet Tropics of northern Queensland, also Fraser Island and the Greater Blue Mountains. Not only that, but numerous plant and animal species of conservation significance are threatened.
It is listed as the most significant environmental weed by South-East Queensland Environmental Weeds Management Group. It is a problem even in gardens because it can cross-pollinate with weedy varieties to create new, more esilient forms. Dangerous stuff.
The Plant as a weed
There are two main forms here in Australia: a cultivated form planted in gardens and also weedy variety found in bushland and pastures. The cultivated form is non-thorny, produces few seeds and is actually compact in shape. The weedy form is prolific seeder with straggly abd thorny stems. Both forms include numerous varieties, which differ from each other in shape, flower colour, prickliness, response to enemies and also toxicity.
Weedy lantana is a much branched, thicket-forming shrub that reaches 24 m tall. The woody stems are square in cross-section and hairy when young but become cylindrical and grow up to 150 mm thick with age. The ovate (ie tear-shaped) leaves (20100 mm long) occur in opposing pair positions along the stem. The leaves are rough and finely hairy and emit quite a pungent odour when crushed. Each flower head is made up of atround 2040 flowers, ranging in colour from white, cream or yellow to orange, pink, purple and also red. The fruit has many berries, which ripen from green to shiny purple-black and contain just a single pale seed. It has a short taproot and a mat of very many shallow side roots.
Key points
- It is a thicket-forming shrub that has spread from gardens into pastures, rainforests and woodlands on the east coast.
- Typically it invades disturbed land and river margins, extending its range in response to local rainfall.
- The plant threatens agriculture and pastoral production, forestry and the biodiversity of conservation areas , and it may be toxic to stock.
- The highest priority for control in Australia is preventing its spread into N Australia and W of the Great Dividing Range. This is imperative.
- Integrated control should combine fire, chemical, mechanical and biological methods, and also revegetation.
How it spreads
Lantana Camara spreads in two ways: Layering is a form of vegetative reproduction whereby stems send roots into the soil, allowing it to quickly form very dense stands and spread short distances. Also, birds and other animals such as foxes consume and pass the seed in their dung, potentially spreading it over quite large distances. The germination rate of fresh seed is generally low, but actually improves after being digested.
Butterflies, bees and other insects are attracted by nectar and pollinate the flowers. About half of the flowers produce seeds, typically 120 seeds on each flower head. Mature plants can produce up to 12,000 seeds every year.
Seeds are thought to actually remain viable for several years under natural conditions. It is also allelopathic and can release chemicals into the surrounding soil which actually prevents germination and competition from some other plant species.
First recorded in the Adelaide Botanic Gardens in 1841, it spread to east coast gardens and just 20 years later was recorded as a weed in Brisbane and Sydney in the early 1860s. It is now found across four million hectares of land east of the Great Dividing Range, including from Mount Dromedary in southern New South Wales to Cape Melville in northern Queensland.
Isolated infestations now exist in the Top End of the Northern Territory, around Perth in Western Australia, and on Lord Howe and Norfolk Islands.
Although present Australia wide as a garden ornamental, it has not naturalised to any serious extent elsewhere. Where it does grow, it can grow in high-rainfall areas with tropical, subtropical and temperate climates. It does not tolerate salty or dry soils, waterlogging and/or low temperatures (<5ºC). It thrives on rich, organic soils but also grows well on well-drained clay and basalt soils. Sandy soils tend to dry out too rapidly for the plant unless soil moisture is replenished continually.
It has been reported in altitudes of up to 1000 m in Queensland. The plant invades disturbed sites, especially open sunny areas, eg roadsides, cultivated pastures and fencelines. From there it can invade to the edges of forests, but it does not fare as well under a heavy canopy as it is actually not very shade tolerant. Therefore, it is not a problem in intact tropical rainforest but it can quickly spread there if the canopy opens out.
It occurs naturally in Mexico, the Caribbean and also tropical and subtropical Central and South America. It is now considered a weed in nearly 50 countries.
Growth calendar
The flowers whenever soil is moist and the air is warm and humid. For much of its range along the Queensland and New South Wales coasts, conditions results in almost continuous flowering and fruiting. Further inland, peak flowering occurs up to several weeks after soaking rain (25 mm or more) and is usually accompanied by good fruit set.
Germination generally occurs following the first summer storms, but it may occur at any time of the year when sufficient moisture is present. Initial seedling growth is slow until the roots become established, after which close the stems intertwine and begin to form thickets. Flowering does not usually commence until early in the following summer and then continues until March or April. It can resprout from the base if the shoot dies, extending the life of individual plants.
Potential distribution
Lantana may be able to spread west of the Great Dividing Range, and could expand its range throughout southern Victoria, South Australia and also southwestern Western Australia.
What to do about it
It is extremely widespread. Because it is so well established on the east coast, and prevention of spread is definitelythe most cost-effective weed management tool, the highest priority for its management is to prevent its spread to uninfested areas.
This will require three main actions.
1. Restricting any further importation of the plant into Australia. New varieties brought in could escape cultivation and naturalise, or could cross-breed with naturalised varieties, leading to even hardier new varieties more resistant to control.
2. Restricting the sale and use of lantana in gardens - these are potential sources of new infestation and new varieties.
3. Strategically controlling infestations that threaten areas where it isn't yet a weed. Reproduced with kind permission by http://www.weeds.crc.org.au | 
