Valued for being colourful and requiring little maintenance, ornamental lantana is still being used extensively in landscape design, and in public and private gardens.  This attitude is now changing.

Real costs of lantana
Any benefits of lantana are far outweighed by its negative effects. Lantana camara is a fast growing, semi deciduous poisonous shrub that can rapidly form dense thickets.  Lantana camara is an invasive species and has covered large areas in India, Australia and much of Africa.  It colonises new areas when its seeds are dispersed by seed eating birds. Once it reaches an area, Lantana camara spreads quickly. It coppices so well, that efforts to eradicate it have completely failed. It is resistant to fire, and quickly grows in and colonises burnt areas.  Lantana often forms thickets in sunny open areas, commonly invades disturbed sites such as roadsides, pastures, and cultivated woodlands displacing indigenous vegetation. It tolerates a wide range of environmental conditions, thriving in both dry and humid climates, is shade tolerant and may dominate the undergrowth of open forests.

Its dense thickets exclude native species through smothering and allelopathic effects (i.e. toxicity to other plants), dominating understorey species and reducing biodiversity of the fauna and flora - this is especially visible in Ishasha, the Southern part of Queen Elizabeth National Park. Shrubs are thorny and dense thickets can obstruct stock and human movement in many situations. Lantana is unpalatable and poisonous to livestock causing photosensitisation, which results in inflammation of the muzzle, mouth, stomach and intestine, leading to death

Lantana is a worsening weed.  The commercial breeding of new forms of ornamental lantana ultimately adds genetic diversity to the weedy forms, potentially decreasing the effectiveness of controls. Lantana may have made itself at home in Uganda, but we need to change the idea that it is an acceptable part of the landscape, or a low-priority weed

Where Lantana Come from?
Lantana camara was introduced to Europe from Central America in the 17th century as an ornamental and then distributed round the globe in conjunction with the spread of colonial empires. This plant is known as a classic example of long range dispersal of an ornamental in warm regions. It is now a major weed pest in over 60 countries, and is considered to be one of the 10 worst weeds worldwide because of its impacts on primary industries, conservation and biodiversity, and the extent of its distribution.  It is spread mainly by birds and through ornamental plantings.

Lantana Description
Lantana is a pungent shrub with many branches. It grows to 2-4 m high with prickly, brittle stems, square in cross section. Stems grow from a robust woody rootstock with numerous shallow laterals which sucker if damaged. It has arching stems that are square in cross-section, with pithy centres and short, backwardly hooked prickles. 
The leaves are 2–10 cm long with toothed edges, bright green on the upper surface and paler green, hairy and strongly veined on the underside.  They grow opposite one another along the stems, and their size and shape depends on the type of lantana, and the availability of moisture.  The plant has a shallow root system made up of a short taproot with lateral roots branching out to form a mat.  The inflorescences (clusters of 20–40 individual flowers) are about 2.5 cm in diameter.   Tightly packed, angular flower buds open from the outside towards the centre of the inflorescence as they mature.  Single-seeded hard green fruit grow in clusters, are about 5–7 mm in diameter and ripen to shiny black or purple fleshy berries.  Berries are edible when ripe though like many fruit but poisonous to humans and livestock if eaten while still green and there have even been reported human deaths from Lantana poisoning.  Crushing the stems and leaves produces a strong characteristic smell.  It is sometimes known as "red (yellow, wild) sage", despite it's classification in a separate family to sage (Lamiaceae), and a different order to sagebrush (Asterales).

Importance of Plants
Approximately 80% of all medicines on the market are made from plants or improved from material that originally came from plants. 90% of the world's population relies upon 20 plant species for their main source of nutrition.

What is a weed?
A weed is a plant growing in a place where it is not wanted. Usually competitive and adaptable species, weeds employ highly effective methods of reproduction and are often difficult to kill.

Weeds are species that invade and persist within agricultural and natural ecosystems, displacing crops and native species through use of space, light, water, nutrients and pollinators.  Weeds also interfere with fire prevention, harvesting, harbour pest animals and crop diseases, taint milk and render hay crops unsaleable.

Weeds are not wanted because they pose one of the most serious threats to natural ecosystems of the world (second only to land clearing). The cost of weeds is substantive - lowering farm incomes and increasing food costs.  It is essential that all land managers are actively involved in weed management to reduce the impact on agriculture, biodiversity and the community.

Naturalisation
Lantana camara has become naturalized in tropical and warm regions worldwide. In the Kenyan highlands it grows in many areas that receive even minimal amounts of rainfall. It can be seen in the wild and along footpaths, deserted fields, and farms and has been naturalised where the climate is close to its native climate, with high heat and humidity.
Invasion
Long distance spread is the result of fruit-eating birds eating the fruit and dispersing the seeds in their droppings. Lantana colonies increase in size by suckering and seedling growth within and along the edges of thickets.
Reproduction and spread Dispersal of seed
birds are the main agents of dispersal, as they spread seed in their droppings.  Some mammals also eat and disperse lantana seed.  Studies have shown that germination is actually more likely if the seed has travelled through the gut of a bird or mammal. 
Vegetative spread
Lantana can spread via a process known as layering, where horizontal stems take root when they are in contact with moist soil.  It will also reshoot vigorously from the base of vertical stems (and more slowly from the rooted horizontal stems), although it does not sucker from damaged or broken roots
Pollination
Insects such as butterflies, moths and bees pollinate the flower clusters.  Approximately half the flowers form clusters of singleseeded berries.  A single plant can produce up to 12,000 fruit each year. 

Reproduction and spread Seed viability
Germination
Activities that increase light intensity and soil temperature will stimulate germination of lantana seed.  These include human disturbances such as clearing, construction and inappropriate burning; and pest animal activity such as pig rooting and rabbit burrowing.  Seeds need warm temperatures and sufficient moisture to germinate.  Germination is reduced by low light conditions. 
Longevity
Lantana is very long-lived under favourable conditions.   Constantly renewed growth at the base of stems ensures its persistence.   Plants tend to die only under extremely stressful conditions, such as extended drought or complete shading through canopy closure. 

Gardens and landscaping - Ornamental lantana increases the risks
Lantana has become popular in gardens, for being colourful, its hardy nature and requiring little maintenance. It is not affected by pests or disease, has low water requirements, and handles extreme heat. Some commercial varieties previously thought to be sterile can in fact produce viable seed or hybridise with wild varieties, increasing genetic variation in the species complex. This continual variation may enhance the ability of lantana to adapt to new environments.

Ornamental Lantana montevidensis
Ornamental varieties of L. montevidensis (creeping lantana) have also been developed for sale in nurseries. In some cases, it is the weedy purple-flowered form capable of producing fertile pollen and seed that is grown in gardens as an ornamental. The ornamental forms of creeping lantana are sterile, flowering profusely without setting seed. However, the pollen from weedy forms can pollinate ornamental forms resulting in viable seed, which adds to the genetic base of weedy creeping lantana. Allowing the sale and use of any ornamental lantana therefore adds to the genetic diversity of the lantana species complex, and potentially enhances the ability of weedy lantana to spread by adapting to new environments and resisting control by herbicides and biological control agents.
How to get rid of Lantana Control techniques
Mechanical control methods include hand-pulling of seedlings, slashing, grubbing (digging out by the roots – effective for single plants if all the roots are removed), felling and bulldozing.
Herbicides are an important tool for managing lantana in many countries.  Herbicides should be applied when plants are actively growing in spring or summer. Complete coverage is essential to achieve effective results.
Biological control attempts to control weeds by introducing the weed's own natural enemies. A promising option for lantana is leaf rust, but research is also continuing into the biocontrol potential of a bud mite, and several pathogens and beetles. A new biological control agent Ophiomyia camarae (herringbone leaf-mining fly) has been approved for release in South Africa.

Regrowth and re-infestation
Lantana is an extremely hardy and persistent weed.  It can achieve remarkable drought tolerance under temporary dry conditions by dropping its leaves.  Dry lantana can appear to be dead, but will reshoot from the base of the stems after rain.
Without appropriate follow-up, initial control efforts in all situations are almost certain to result in re-infestation through the regrowth of existing plants and germination of new seedlings. 

A concerted effort is required for the control of this major weed. A re-evaluation of attitudes to lantana is necessary to prevent worsening of the lantana problem and it’s potential future spread.  Without a concerted effort, it will continue to infest new areas of natural ecosystems and productive land.  We cannot rely on IUCN (the International Union for Conservation of Nature) or... it's to far out of control.