Cuscuta campestris (Family: Convolvulaceae)
Dodder, gewone dodder (Afrikaans); umankunkunku; unyendenyende (isiZulu)
The native range of this species is obscure. It is thought to be native to North America (Canada, USA and Mexico) and parts of the Caribbean. It is possibly also native to parts of South America. Found throughout south Africa. Invasive status in South Africa as category 1b.
Cuscuta campestris also attacks a wide range of naturalised species and native plants that are growing in grasslands, open woodlands, coastal vine thickets, gardens, degraded land, riparian zones (banks of watercourses) and wetlands.
Cuscuta campestris is an annual stem parasitic plant. It lacks normal roots and leaves, but does bear flowers and fruits. Cuscuta species have a very distinct appearance, consisting mainly of leafless, smooth, yellow or orange twining stems and tendrils, with inconspicuous scales in the place of leaves. C. campestris has yellow to pale orange true stems, about 0.3 mm in diameter, which generally do not twine and attach to the host, but produce tendrils of similar appearance which form coils and haustoria - a specialised root-like sucker which penetrates another plant (a host) and obtains water and nutrients from it (Dawson, 1984). The seedling has only a rudimentary root for anchorage. The root and shoot below this initial attachment soon die, leaving no direct contact with the soil. C. campestris stems are thread-like, yellow or pinkish-yellow in colour, are much branched and grow to 0.8 mm. The stems entwine themselves around host-plants, with the help of haustoria. C. campestris flowers are white or greenish, aggregated in groups of 3-8 in spreading inflorescences, cymose (flat-topped or convex flower cluster in which the uppermost flowers open first). Corolla is 2-2.5 mm long, bell-shaped. Calyx is 1.5-2 mm long, hemispherical. Flowers have 4-5 sepals which are united at base. The fruit is a light-brown, 2-4-seeded boll. Seeds are oval, light-brown or brownish, to 1.25-2.5 mm long, 1-1.5 mm wide.
Cuscuta campestris is a parasite of a wide range of herbaceous plants. It can be a serious weed when broad leaved crops are grown as perennials (e.g. lucerne, clovers, citrus and sugar beet). It causes damage by absorbing food material from the host plant. The dense mat of stems it produces can also entangle the host and cause shading of the ground vegetation layer. C. campestris has been listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment), Hawaii and most Australian states.
Cuscuta campestris seeds are dispersed by wind, water, birds, other animals, and by man on machines and planting material contaminated by dodder seeds. C. campestris reproduces by seed which can germinate under relatively high temperatures. The seeds can remain viable for more than 3 years. The seeds after being ingested, are said to maintain their germinating capacity and vitality for up to10 years. Immature seeds are said to germinate faster than mature ones. However, though seeds are viable and germinate readily, Cuscuta species can only survive the seedling stage if they get a host immediately after germination (before the food in the cotyledons is finished) and therefore their major means of dispersal at a local scale is plant fragments that are carried by people (especially children) because of their bright colour and appeal and later throw them on other vegetation where they attach very fast and send their haustoria into their vascular systems.Management
The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.
The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.
Cuscuta campestris can be controlled by planting uncontaminated crop seeds. Young seedlings are readily destroyed by shallow tillage before or after crop establishment. Hand-pulling is suitable only for scattered infestations as the infested crop plants have to be removed with the parasite. Scattered infestations can also be controlled by using a hand-held flame gun. More extensive infestations in lucerne are also sometimes treated with overall flaming, as the crop is able to recover. Close mowing is an alternative means of control in lucerne and clovers. Rotation with non-susceptible crops such as cereals can be helpful.
It is important to control C. campestris on vegetation along road sides, boundary-strips and waste lands. Crop rotation of 3-4 years cycle by unsusceptible crops/cultures.
Due to its spread by people, one of the best methods of control is to sensitize people to desist from carrying plant parts and if they do, to destroy them or to dry them on a surface other than on living plants and then to dispose of them by burning (D.L.N. Hafashimana pers. comm.).
A variety of biological control agents have been trialed with variable results.