Lantana Camara is a flowering plant that belongs to Verbenaceae family
Abstract
Lantana camara was introduced as an ornamental plant in Australia but developed into one of the most harmful weed in the country. Today the plant has spread to over 5 million hectares causing various problems to native species within the ecosystem. The plant produces toxic components that are harmful to both animals and other plants. This has triggered the reaction of various stakeholders to control the weed. The researcher can up with differing methods and ideas of controlling lantana camara which varies from mechanical, chemical and biochemical control. However much of their effort have gone into waste as these plant has proven to be stubborn. This paper will highlight the literature on Lantana camara with an aim of coming up with best management technique that can be applied on lantana camara. This paper used a survey research design as it assisted the researcher to collect the data from the past to the present. Present research suggest that the Australian government has applied biocontrol methods for several decades without coming up with specificity of biochemical agents that causes effects on lantana camara
Literature Review
This chapter presents previous studies conducted by other researchers on the management of lantana camara weed in Australia and other parts of the world. The chapter is divided into sections with section 2.1 representing a brief introduction of the weed. Section 2.2 examines the effects of lantana on animals while section 2.3 examines its effects on plants, vegetation and forestry. The role of lantana camara on Bell miner associated dieback is discussed in section 2.4. Section 2.5 discusses the relationship that exist between Lantana and fire. Section 2.6 discusses the management practices applied in the control of lantana camara. The current practices and recommendations will be discussed in section 2.7 and 2.8 respectively.
2.1 Introduction to Lantana Camara
Lantana Camara is a flowering plant that belongs to Verbenaceae family. Lantana camara has its origin in South and Central America. It was introduced to more than 60 tropical and subtropical countries across the world as a horticultural plant making but it has become invasive naturalizing itself in various environments (Australia, 2020). Lantana Camara weed is one of the most harmful and popular weed across the globe. The weed has negative impacts both in animals and plants. (Sharma, Raghubanshi, and Singh, 2005).
The International Union for Conservation of Nature (IUCN) includes Lantana camara weed in the list of the world’s worst invasive species. The Department of Natural Resources, Mines and Energy (DNRME) of Australia describes Lantana camara as a weed that has National significance as well as including it the list of the 20 most problematic species in the region. Lantana camara was brought to Australia as an Ornamental plant in the 1840’s after which it established itself as an invasive weed. The weed was originally recorded at Adelaide Botanic Gardens in 1841. By early 1860’s it had spread to the east coast to Brisbane and Sydney where it was first labelled as a weed (Patrick, 2020). Eastern Australia experiences the effects of the fast spreading of lantana camara as the weed occupies more than four million hectares in the region alone (Berry, Wevill and Curran (2011). The weed has not naturalized
Due to its economic effects and its potential to spread over large areas, Lantana Camara is considered as one of the worst weeds in Australia. Lantana Camara reduces productivity of forestry and pasture land as it forms impenetrable thickets that spreads over natural bushland and pasture. This spread leads to completion for resources with wanted crops. The weed has detrimental effects to Australian environment as it can act as a fuel agent in case of fire (CRC of Australian Weed Management, 2003). Lantana Camara is a threat to the agricultural industry as it has the potential to cross-pollinate with other unwanted plants leading to the development of more resilient species.
There are two species of lantana camara in Australia with one species being cultivated while the other one is a weedy variety that encroaches bushland and pastures. The difference between the two varieties is in the ability to control them. The cultivated variety is easy to stop as it bears no thorn, produces less seeds and is less dense as compared to the thorny weed variety. The weed variety grow as a shrub that is approximately 2-4 m tall,150mm thick, with rough leaves that appears in opposing pairs along the stem with a length of between 20 -100mm. the leaves produces pungent odour when crushed (CRC of Australian Weed Management, 2003). They also produce that ranges in colour from white, yellow, orange, pink red, purple. Lantana camara’s fruit are purple-black when ripe and green when young. The plant has a tap root with a dense network of shallow roots. Lantana camara inhibit the growth of natural species due to its dense impenetrable thickets which invade areas which are to be occupied by desirable species.
2.1.1 Spread of Lantana Camara Weed
Lantana camara can either spread through layering of its roots in the soil or by being spread by mammals and birds. Lantana camara has the ability of sending its roots quickly in the ground forming a dense network of short roots when they spread through layering (CRC of Australian Weed Management, 2003). Mammals and birds that consume the weed helps in the dispersion of lantana camara’s seed over large distances through their droppings. These makes the weed to germinate in disturbed areas as digested seeds has an improved rate of germination over fresh seeds. Lantana is toxic to other plants and is viable for up to 36 months while other species may be viable for up to 11 years (“Lantana: noxious weed or great habitat?”, 2020).
Lantana weed has a capability of producing approximately 12000 seeds annually. Butterfly and birds play an important role of pollination as they collect nectar from the plant (CRC of Australian Weed Management, 2003). The weed is problematic to other plants as it produces chemicals in the surrounding soil thus preventing the germination of other plants particularly the native flora consequently taking up the entire land (Patrick, 2020).
2.1.2 Habitat of Lantana Camara
Lantana grows in a variety of soils as well as wide ecological zones as reflected by its geographical distribution. However the weed will do well in tropical, subtropical and temperate climates that experiences high rainfall (CRC of Australian Weed Management, 2003). The weed does well in wet soils that have a temperature of more than 5 degrees. Lantana occupies disturbed land especially such as roadsides, canals and forest edges (Day et al, 2013). The plant also encroaches forest areas where logging has occurred however, it does not grow well in shady areas. This fact means that lantana can only spread in area where there is loose tropical rainforest cover. The southern parts of Australia do not experience dense invasion by Lantana camara as they are too cold which limits the growth of the weed. The arid Inland Australia is however not invaded badly by the weed as it experience dry stress inhibiting its spread (Taylor, Kumar, and Reid, N. 2012).
Lantana’s rate of spread in northern Queensland has been inhibited by lack of human disturbance though there large areas where it can spread to in the region (DERM, 2010). Climatic changes in Australia has led to changes in the zones that the weed invades as suitable areas become unsuitable and vice versa. The northern part of Australia has is becoming unsuitable for the growth of the weed while new opportunities are becoming available in the south. (Johnson, 2009).
Although soil disturbance leads to the growth of lantana camara weed, it may also be unsuitable for the growth of the weed through modification of conditions. For example areas that are suitable for the growth of the weed as they are already occupied by stable ecosystems which have been modified by humankind settlement, urban areas or in agricultural ecosystem. Areas where extensive farming is carried out may be unsuitable for the growth of the weed as this areas undergo rigorous weed management strategies that inhibit the growth of lantana weed (Taylor, Kumar, and Reid, N. 2012). Hence lantana will be eradicate even before it utilizes the conditions for spread produced by irrigation of the land. Developed or modified area such as urban setting minimizes the chance of lantana spread by providing poor conditions for its growth.
Grazing land that are inhabited by natural vegetation are more prone to lantana’s invasion as they management is not that intensive. In a study conducted in Queensland and NSW on the distribution of lantana camara the researchers concluded that there was a high level of invasion on grazed natural vegetation (DERM, 2010 applied in Taylor, Kumar and Reid, 2012). Taylor, Kumar and Reid (2012) argued that areas that were used for grazing in Australia were prone to invasion by the weed as compared to agricultural land. The researchers further argued that areas which had been cultivated and abandoned for grazing were less productive due to the invasions by the weed.
2.2 Effects of Lantana Camara on Animals
Veterinary doctors are often disturbed by the effects of harmful plants that leads to reduced productivity and increased mortality rates in livestock (Diaz, 2011). Sharma et al.
(2007) argued that individual characteristics of an animal which includes the age, species, the body conditions as well as the nature, part and quantity of the toxic material taken will greatly determine the level of toxicity effect for that particular animal. Invasive toxic plants have turned out to be one of the major threats to the biodiversity and the ecosystem as well as livestock (Kumar, Katiyar, Kumar, Kumar & Singh, 2016). Invasive plants are predators that leads to spread of diseases in animals as well as in plants (Drenovsky et al., 2012).
Lantana camara is one of the most toxic and invasive plant in the world. Lantana weed has led to the loss of agriculture and forest ecosystem as well as causing high mortality rates in animals (Kumar et al. 2016).
In Australia most of the varieties of Lantana camara weed are poisonous to domestic animals such as sheep and cow, with only three varieties said to be nontoxic (“Invasion, establishment and spread of Lantana (Lantana camara) – key threatening process listing”, 2020). Taxon which refers to the pink variety of lantana camara is a nontoxic weed that is used to feed animals in New Zealand (Black and Carter, 1985 cited by Kumar et al, 2016). The genetic factors are more associated with toxicity as compared to environmental factors. Lantana leaves are poisonous to most animals including goats, sheep, buffalo and cattle. The goats are less resistant to Lantadene poison produced by lantana camara while cattle’s, buffalo and sheep are highly prone (Kumar et al, 2016). Lack of prior feeding before sending animals to graze in pastures affected by the weed as a result of fodder scarcity maximizes the possibility of toxicity effects in animals (Sharma and Markar, 1981, Cited by Kumar et al).
Due to scarcity of fodder cattle’s are forced to take lantana camara weed which they mainly take its leaves. Feeding on these leaves exposes cattle’s to severe dermatitis making them to look dull (Negi et al., 2019). Lantana seed and leaves contains a poisonous and photosensitivity component that leads to hepatotoxicity when consumed by grazing animals. Making of silage from lantana camara’s leaves doesn’t make the poisonous species less toxic hence microbial reaction does not make its leaves to be a palatable fodder. Human being are not spared by the weed as they are affected by ingestion of green berries.
2.3 Effects of Lantana Camara on Plants, Forestry and Vegetation.
Lantana camara has various effects on plants which range from allelopathy effects, monopolization of resources, smothering, spread of pest and disease among others. Lantana camara has a dense network that forms a canopy that reduces the availability of light to ground inhibiting the growth of grasses and other ground cover vegetation. Consequently, these reduces the rate of rain absorption while increasing the amount of run-off water and soil erosion (Sharma, Singh and Tiwari, 2009). However a strong debate exists on the contribution of lantana camara role in soil erosion (Day et al, 2003). The spreading nature of lantana camara has made it to change the structure of the terrestrial environment. Lantana eliminates natural species by forming a dense network of thicket.
Lantana inhibits the growth of neighboring plants by altering the light and temperature as well as out competing for soil nutrients by forming a dense network of thickets (Sharma, Khare & Aslam, 2017). Lantana camara excretes chemicals that affect the metabolism of neighboring crops thus inhibiting germination (Qasem JR, 2006). Some poisonous compound of lantana camara interfere with cell division of germinating seeds while its residues of the weed causes cell elongation. Lantana is also affects the physiological needs of the neighboring plants by altering the permeability of the cell membrane, ion uptake, respiratory chain, damage to DNA and protein as well as inhibition of enzymatic activities causes death (Mishra, 2014).
The intrusion caused by invasive plants threatens the integrity and functioning of ntural ecosystems across the globe. The structure and composition of the ecosystem are altered by the completion of resources caused by invasive plants. The availability of water and fire regimes also experiences the threat of these plants (Lambert, Reid and McDonald, 2017). Natural species of mature plants covers may be displaced through inhibition of successive growth by invasive plants (Yiurkonis et al., 2005). Lambert, Reid and McDonald argued that invasive plants pose a danger to natural plant species as it inhibits their growth by bringing competition for nutrients, light and space. Hiremath et al.(2012 argued that regeneration of the natural species in invaded areas is inhibited by invasive weeds resulting to fewer young plants as compared with areas where there is no invasion.
The research on invasive plants on natural species is possible as one can be able to directly measure the changes that have occurred since the invasion of these plants (Turner and virtue, 2006). Recruitment inhibition can be studied through an experimental studies. This experiment will involve removal of the invasive plant from an area and then observing the changes that will occur in the native species population (Lambert, Reid and McDonald, 2017). The experiment however, maybe affected by the influence of residual of invasive plants on the concentration of soil nutrients.
Allelopathy leads to the dominance of lantana camara in various ecosystems as it helps the weed to alter the growth of neighboring plants by intoxicating the soil by the use of their seeds, leaves and residue (Putnam and Duke, 1978 cited by Sharma et al, 2007). Hughes recorded the effects of allelopathy caused by lantana in Australia (Sharma et al, 2007). Kong et al (2006) argued that the leaves of lantana camara suppressed the growth of aquatic weeds. Kong et al further observed that the biomass of aquatic weeds was reduced within & days as a result of applying an extract of lantana leaves. The protein pattern and the radicle growth of tomatoes was altered by the aqueous leachates of lantana camara (Romero- Romero, 2002 cited by Sharma et al. 2007). The allelopathy in lantana camara is synthesized in its leaf before it is translocated to other components of the plant (Sharma et al, 2007).
Lantana spread all over the rainforest is one of the biggest problem faced by the Springbrook National park caused by seed dispersion along the edges of lantana patches (Stock, and Wild, 2002). Lantana can lead to the damage of the entire rainforest if it is left unchecked due to its ability to out compete natural species in areas that are regularly disturbed. Sufficient canopy will prevent the inhibition of regeneration of native plants by lantana in disturbed moist subtropical rainforest (Williams, 1969 cited by stock and wild). Lantana cannot thrive under closed forest canopy of subtropical rainforest which makes it difficult to displace native species in the south-east Queensland (Stock and Wild).
Sufficient maintenance of local sources of re-establishment in rainforest areas that experiences lower rainfall may lead to the replacement of lantana by local species (Anon, 2000 cited by stock and wild, 2002). However the competitive edge of lantana will make it thrive in the rainforest regions that experiences high rainfall even if there is maintenance of local sources of regeneration. Lantana inhibits the growth of grass in the northern Queensland leading to the prevention of low intensity fires in disturbed rain forest areas (Stock and wild).
2.4 Role of Lantana Camara on Bell Miner Associated Dieback
Bell miner associated die back refers to the decline in the levels of canopy in Eucalyptus crown that occupies the colonies of bell miners. Eucalyptus in Coastal and South-eastern Australia undergo a condition of defoliation and regrowth which can result to its death if subjected to the condition for prolonged period of time. BMAD has been shortlisted in the NSW threatened Species Conservation Act of 1995 (Silver and Carnegie, 2017). According to a survey conducted by the Forest Health Unit in over 300, 000 hectares of forest land in South wales, over 20000 hectares of forest had been attacked by bell miner associated dieback (Haywood and Stone 2011). Although the current e4ffect of bell miner associated dieback unknown, locally conducted surveys and observations shows that the extent of BMAD is increasing (Wardell- Johnson et al, 2005).
The Coastal and South-Eastern Australia is a habitat to insectivorous birds who are associated with reduced variety of avian species (Kemmerer et al., 2008). The ability of bell miner to do away with other insectivorous avian species as well as hindering the effectiveness of invertebrate predators has contributed to the increased numbers of herbivorous insects. These herbivorous birds especially the sap-sucking insects cause premature leaf death that eventually causes dieback of the affected trees (Haywood and Stone, 2011).
Most researchers have linked bell miner associated die back in Eucalyptus to the effect of a dense network of shrubby vegetation that develops in an area with sparse eucalypt canopy (Poiani, 1993; Pearce et al, 1995, Higgins et al, 2001: stone et al, 2008 cited by Haywood and Stone). The dense network of lantana camara provide ample areas where bell miners can build their nests (Clarke, 1988 cited by Haywood and Stone 2011). According to NSW lantana weed is heavily associated with bell miner associated dieback. BMAD is promoted by sparse canopy which makes light available facilitating the growth of lantana camara, a home to bell miner nesting (Specht, 1983; Stone et al, 2008).
2.5 Lantana and Fire
Some researchers have argued that there is a symbiotic relationship between fire and lantana camara. According to them, lantana camara will be established after fire-related disturbance. On the other had the alteration of ecosystem structure as a result of the spread of lantana camara will lead to promotion of high fire frequency and intensity (Berry, Wevill and Curran, 2011). Human activities such as land fragmentation, changes in the use of land and deforestation as well as natural fire increases the susceptibility of the ground to invasion of lantana camara. Leading to the repeat of the cycle (Hiremath and Sundaram, 2005).
Lantana can burns easily when exposed to high and dry conditions even when green (Sharma et al, 2005). On the other hand lantana camara leads to the spread of fire in the ecosystem. Climbing Lantana stems have the capability of rising up to 20m making it to reach the canopy of the forest. This rise makes them to expose the forest to burning in case of fire outbreak (Tireman, 1996 cited by Nigel 2019). Lantana has various effects on the ecosystem, these include loss of natural biodiversity, formation of dense network that suppresses regeneration of forests, promotion of fire and providing habitat to destructive organisms.
However, low moderate intensity fire leads to the spread of lantana thickets rather than destroying them. Fire also reduces competing plant species (Sharma et al., 2005). Fire creates conducive environment for the growth of lantana camara.
Fire breaks seed dormancy in lantana resulting to massive growth of the weed. Joshi argued that fire was a factor of enhancing the growth of lantana camara rather than controlling its spread (Negi et al, 2019).
2.6 Management of Lantana Camara
Lantana camara has invaded more than five million hectares in Australia (Bhagwat, Breman, Thekaekara, Thornton & Willis, 2012).Researcher do not agree on the best practices for controlling the spread of lantana camara. The government of Australia in collaboration with non-governmental actors have taken aggressive measures in the fight against the spread of lantana camara. The control of lantana in Australia began in the early 20th century with the number of controls increasing in the 1970’s (Haseler, 1979 cited by Bhagwat et al, 2012). The control of lantana between 1959 and 1983 was mainly by the use of biocontrol as indicated by the Forestry Commission of New South Wales reports (Bhagwat et al). Despite the efforts placed during those years in the control of lantana the weed continues to thrive leading to application of other methods. These methods include manual control, biological control, and chemical control.
2.6.1 Biological control of Lantana camara
The foundations on the application of biological controls in the fight against the spread of lantana camara are formed on the premises that insect herbivory reduces the fitness of attacked weeds. These notion rets on the assumption that the death of attacked plants will lead to the reduction of lantana camara’s population density (Zalucki, Day, and Playford, 2007). Researchers argue that plants that translate into weeds after being introduction, spread rapidly than they do in their natural grounds in the absence of herbivory (McEvoy, 2002; Vilà, Maron & Marco, 2005)). These researcher argue that they argue that in order to control these plants there is a need to introduce herbivores to feed on them. Most researcher have dwelled on testing the host specificity of potential targets loosing concentration on the effect of established agents on the weed (Zalucki, Day, and Playford, 2007).
The success of biological agents introduced in the control of lantana programme depends on the phenotype of the lantana species (Haseler, 1966 cited by Day and Neser, 2000, July). The success of biological methods is hard to determine. This id due to the fact researcher who advocate for biocontrol uses a lottery approach in the fight against lantana camara. The researcher will introduces a new agent once they perceive that lantana camara is not under adequate control. This make the process of determining the effects of each agent to be difficult if not impossible (Zalucki, Day, and Playford, 2007).
Scholars argue that the control effect of introduced agents is not realized as a result of competition among the agents (McEvoy, 2002). Other researcher have argued that the size of invested land should be proportri0onal to the amount of agents introduced (Lawton, 1993, Cited by Zalucki, Day and Playford, 2007). These researchers further argued that the impacts of biocontrol agents may be limited as a result of hybridization. Most of the agents are unable to adapt to the adaptation mechanism of lantana camara (Hokkanen,and Pimentel 1989 cited by Zalucki, Day and Playford); ( Myers, 2000)
2.6. 2 mechanical control
Lantana camara can be removed by the use of tractors and bulldozers (Zalucki, Day and Playford, 2003). The method is efficient as it minimizes the risk of damaging neighboring vegetation as well as killing the weeds that occur in small isolated clumps. Mechanical method may not be applicable in areas that experiences high rates of soil erosion or heavily invaded areas. The method also facilitates regrowth of lantana camara weed especially in areas that the root stock was not completely removed. In dry areas the use of a bulldozer is encouraged especially when there is immediate application of pasture grass after removing the weeds. Herbicides are later used to control any regrowth of lantana camara (Lakshmi and Sekhar, 2018). Mechanical control may not be applicable in rocky areas and very extensive areas hence it’s a low-efficiency technique (Sharma, Raghubanshi and Singh, 2005).
2.6.3 Chemical Control
Researchers have come up with a wide variety of herbicides to control lantana camara which include glyphosate, imazapyr, fluroxypyr among others (Priyanka, 2013) . Herbicides may be applied at the lower back of the stem or applied on top of a fleshly cut stem in cases where the plant is tall. In cases where lantana weeds are less than 2m foliar spraying which includes spraying the entire crop should be applied (CRC for Australian Weed Management, 2003).
The effectiveness of herbicides is unknown despite the danger they pose to the ecosystem. These herbicides interfere with the food chain, leads to water pollution as well as destroying soil fertility (Priyanka 2013).
2.7 Current Best Practices
As discussed in section in 2.6 there is no effective control techniques for lantana camara. Areas which are heavily invaded may difficult to control especially if the land value is low. However physical methods can be applied to control small invaded areas while fire can be used to clear large areas but with great precaution. Chemicals are more effective when applied to regrowth lantana camara after initial control. Since all these methods have their own limitation it would be important for planners to incorporate Lantana camara in generating income to affected communities (Priyanka and Joshi, 2013). Lantana camara may be applied field of medicine, crafting among others.
Lantana camara has been applied extensively in the field of herbal medicine. In a study conducted in India it was found out that the chemical constituents of the weed had some antimicrobial, fungicidal, insecticidal and biocidal activities (Sharma et al, 2007). Oil extracted from lantana camara has been applied in the treatment of leprosy (Priyanka and Joshi, 2013).
Although the twigs and stems of lantana camara are less efficient as compared to other wood varieties, the plant has been use in provision of bio fuel (Varshney et al, 2006). Lantana camara has been suggested as a replacement for wood and bamboo in the paper industries. Researchers such as Ray and Puri (2007), Naithani and Pande (2009) and Bhatt, Gupta and Naithani (2011) argued that the dense network of lantana camara had a great potential of becoming a source of raw material for paper making industry (Priyanka and Joshi, 2013).
2.8 Recommendations
Lantana camara is one of the most harmful weeds in Australia. Most researchers have prioritized the study of target sites when conducting their study on the chemical, mechanical and biological control of lantana camara. Given that biocontrol methods have been applied for several decades, researchers ought to have come up with specificity of each biocontrol agent in determining the effect of these agents on lantana camara.