Mimosa diplotricha

Witt, Arne, Chimphepo, Lilian, Beale, Tim & Nunda, Winnie, 2020, Distribution of Mimosa diplotricha in eastern and southern Africa and its socio- ecological impacts in northern Malawi, Bothalia (a 9) 50 (1), pp. 1-13 : 2

Mimosa diplotricha as a global invader

Mimosa diplotricha is native to much of South and Central America, as well as the Caribbean ( Holm et al. 1977; Parsons & Cuthbertson 1992). It has been introduced, either intentionally or accidentally, to a host of countries in Asia and Africa. It is a major weed in pastures, plantations and roadsides, and in some situations a serious pest in crops (Caunter & Shibayama 1999; Ogbe & Bamidele 2006; Sulaiman et al. 2004). More than 40 years ago it was already considered to be one of the 76 worst weeds in the world, having been recorded as a weed of 13 crops in 18 countries ( Holm et al. 1977). Holm et al. (1979) regarded it as either a ‘serious’ or ‘principal’ weed in Borneo, Fiji, Malaysia, Melanesia, New Guinea, West Polynesia, Philippines, Taiwan, Australia and Indonesia. It is also a serious weed in the Pacific islands, South-East Asia, Mauritius and Nigeria (Waterhouse & Norris 1987).

In the Philippines, Malaysia, Thailand and Vietnam, mimosa is considered to be an important weed in upland rice (Caunter & Shibayama 1999). It is also one of the three main weed species of kale in Nakhon Pathom Province, Thailand ( Pomprom et al. 2002) and a major weed of cornfields in Malaysia ( Sulaiman et al. 2004). Mimosa densities of 630 000 plants per hectare reduced cassava root yield, 12 months after planting, by 80% in one study area in Nigeria (Alabi et al. 2001). In Benin City metropolis, Nigeria, where it has invaded farms, fallow fields and vacant land, it is regarded as the most noxious of all weeds ( Ogbe & Bamidele 2006). In Papua New Guinea, mimosa has a direct negative impact on the growth, yield and harvesting of sugarcane. Harvesting crops by hand in fields invaded by mimosa is also particularly difficult and even harmful, especially in developing countries where this is a common practice and farmers have no protective gear, as the ‘thorns can cause serious sores on humans’ (Waterhouse & Norris 1987). Mechanical crop harvesters can also be jammed when used in invaded croplands ( Parsons & Cuthbertson 1992).

Mimosa invasions also have a negative impact on pastureland, reducing livestock carrying capacities. Cattle ranches in the Markham Valley, Papua New Guinea ( PNG), spend up to US $130 000 annually on the chemical control of this weed ( Kuniata 1994), because it not only displaces valuable forage species but is also considered to be toxic to livestock (Gibson & Waring 1994; Waterhouse & Norris 1987). In Thailand, 22 swamp buffaloes died 18–36 hours after eating M. diplotricha var. inermis (Tungtrakanpoung & Rhienpanish 1992) . There is also a report of M. diplotricha var. inermis poisoning of a two-year-old Jersey-cross heifer in India (Alex et al. 1991). Trials in Australia have demonstrated that this variety of mimosa is also toxic to sheep, and a report from Flores, Indonesia, suggests that it is toxic to pigs ( Parsons & Cuthbertson 1992).

Mimosa can also change the structure and composition of natural vegetation by climbing over and smothering other plants ( Schultz 2000). In western Australia, dense stands are adversely affecting the growth of native plant species (Werren 2001), posing a serious threat to the ecology of native plants and animals if allowed to spread further (Wilson 2004). It also constitutes a serious fire hazard, especially during dry periods when plants tend to die back ( PIER 2008).

Very little is known about the distribution of mimosa in eastern and southern Africa , and particularly its socio-ecological effects in Malawi. This type of information is critical in guiding management decisions, especially with regard to preventing the further spread of this noxious weed and implementing control where it is already well established. This paper contributes to a better understanding of the distribution of mimosa and its impacts on livelihoods in northern Malawi .