Lantana camara, often simply called lantana, is a flowering plant belonging to the Verbenaceae family. Native to tropical regions of the Americas, it is widely recognized as a significant invasive species across the globe. Its presence in new environments poses considerable challenges to ecosystems and agricultural landscapes.
Understanding Lantana’s Invasive Nature
Lantana’s success as an invasive species stems from several biological and ecological characteristics. It exhibits a rapid growth rate, allowing it to form dense, impenetrable thickets that outcompete native vegetation for resources like sunlight and nutrients. Individual plants can produce up to 12,000 seeds annually. These seeds are effectively dispersed over long distances by fruit-eating birds and other animals, such as rodents, which consume its berries. Seed germination rates often improve after passing through an animal’s digestive system, further aiding its spread.
The plant’s adaptability contributes to its widespread establishment across various soil types and climatic conditions, thriving in disturbed areas like roadsides, degraded lands, and forest edges. Lantana also employs allelopathy, releasing toxic chemicals, including phenolic compounds and triterpenes, from its leaves, stems, and roots into the surrounding soil. These allelochemicals inhibit the germination and growth of other plant species, effectively suppressing native flora and reducing competition. Lantana camara demonstrates resistance to drought and can withstand fire, with natural fires sometimes stimulating thicker regrowth. Its unpalatable nature due to toxicity means it faces less pressure from natural predators compared to native plants.
It is toxic to livestock, including cattle, sheep, goats, and horses. The plant contains pentacyclic triterpenoids called Lantadenes, which primarily cause liver damage and photosensitivity in grazing animals. Symptoms of poisoning include anorexia, depression, jaundice, swelling of eyelids, and sloughing of skin in affected animals. Red-flowered varieties are generally the most toxic, though other color variations can also be highly poisonous.
Impacts on Ecosystems and Agriculture
Once established, lantana impacts both natural ecosystems and agricultural productivity. Ecologically, its dense thickets displace native plant species, leading to a reduction in local biodiversity and altering natural habitats. This displacement can significantly slow down forest regeneration by preventing the growth of new trees. The plant’s presence also disrupts ecosystem processes, such as water and nutrient cycling, and can increase fire risk in some regions due to its large, dry biomass, which fuels hotter bushfires.
In agricultural settings, lantana infestations reduce the availability of grazing land for livestock. Beyond consuming pasture, direct poisoning of livestock by ingesting lantana leaves and unripe berries results in economic losses for farmers. Animals can die within two to four days in acute cases, or take one to three weeks if untreated.
Farmers also report reduced crop yields when lantana is present on cultivated land, with some studies indicating a 26-50% reduction in crop yield. The woody stems and spines of the plant make its removal from agricultural fields challenging, interfering with farming operations like harvesting. These impacts lead to broader economic costs associated with biodiversity loss, reduced productivity, and increased management expenses for landholders.
Global Presence and Spread
Lantana camara originated in the tropical Americas, specifically Central and South America. From its native range, it has spread to approximately 60 tropical and subtropical countries worldwide, becoming a naturalized species across all continents except Antarctica. Its introduction to new regions occurred through human activity, primarily as an ornamental plant due to its colorful flowers and hardiness. For instance, it was brought to Europe by Dutch explorers and later spread to Asia and Oceania, becoming a notorious weed.
The plant was introduced to Australia as an ornamental garden plant in 1841 and became established in the wild within two decades. Similarly, it was brought to India by the British around 200 years ago and has since invaded approximately 13.2 million hectares of Indian pasture lands, as well as forest and fallow regions.
Controlling Invasive Lantana
Managing invasive lantana requires an integrated approach combining multiple control methods. Manual removal techniques, such as hand-pulling, cutting, or grubbing out roots with a mattock, are suitable for small infestations.
For larger plants, cutting stems at about 15 cm from the ground and immediately applying herbicide to the cut surface, known as the cut-stump method, is effective. Basal bark spraying, where herbicide is applied to the lower bark of stems, is another chemical control option for larger plants. Foliar spraying, which involves spraying the entire plant with herbicide, works best on plants less than 2 meters tall and when they are actively growing. Responsible use of herbicides requires careful adherence to application procedures and mix rates.
Biological control involves introducing natural enemies, such as insects or pathogens, from lantana’s native range to suppress its growth and reproduction. While 18 biological control agents have been released in South Africa and 32 in Australia, with 19 becoming established, this is a long-term, research-intensive approach that provides suppression rather than eradication. In India, chemical and biological methods are less favored in protected areas due to potential adverse effects on other biota.
A comprehensive management strategy involves an initial control operation, followed by consistent follow-up treatments for regrowth, missed plants, and new seedlings. Preventing new introductions and early detection of infestations are also important for effective long-term management. In some cases, ecological restoration of weed-free landscapes, such as converting them back to grasslands or forest communities, is undertaken to prevent reinvasion.