Common name: Common dodder, Strangle weed, Goldthread, Devil’s hair (Englsih); Agamula-nethi-wela (Sinhala); Kaskutta (Tamil).
Synonyms: Cuscuta arvensis; Cuscuta basarabica; Cuscuta pentagona subsp. calycina; Cuscuta pentagona var. pentagona.
Two Cuscuta species bave been previously recorded in Sri Lanka, namely C. chinensis, distributed in low country and C. reflexa in montane region. In the last edition of the Flora of Ceylon, it is stated that C.chinensis was reported to be very rare by Trimen and it had increased populations by time of Alston. It is also recorded that the plant was found throughout the southern two-thirds of the island, especially along paddy margins by latter time (Austin, 1998; Dassanayake 1980). However, a recent study by Jayasinghe et al. (2004), reports that the species found abundantly in the lowland of Sri Lanka is different from previously recorded species C. chinensis, and that it matched the character description of C. campestris. According to their study, C. campestris is the species that we find as invasive in Sri Lanka. The characteristic feature of the species is the more exposed capsule.
Cuscuta campestris is an angiosperm parasite that adapts to the life cycle of its host, and has a very distinctive appearance. It has leafless, glabrous, yellow or orange stems and tendrils, bearing inconspicuous scales in the place of leaves. These tendrils produces haustoria - a specialised root-like sucker which penetrates another plant (a host) and obtains water and nutrients from it.The true stems are about 0.3 mm in diameter. They generally do not twine and attach to the host, but produce tendrils of similar appearance, arising opposite the scale leaves, which form coils and haustoria (Dawson, 1984). Flowers, each about 2 mm across, occur in compact clusters 1-2 cm across. Seeds are irregular in shape, rough-surfaced, about 1 mm across. The seedling has only a rudimentary root for anchorage with maturity the root dies as the plant become fully parasitic.
Morphologically similar species:
Other species of the Cascuta genus that can be misidentified with C. campestris are C. chinensis and C. reflexa (see the taxonomic note abow).
History and introduction:
C. campestris is native to North America but has been introduced around the world and has become a weed in many countries. A probable cause of its introduction in Sri Lanka is through imported contaminated grains from China or other countries (Jayasinghe et al., 2004).
This species has a wide range of hosts; it is highly adaptive to various climatic conditions and tolerant of temperatures from mild to tropical hot, and is therefore present in many countries throughout the world. In Sri Lanka, Cuscuta is widely distributed in, but not limited to, the dry zones such as Anuradhapura, Polonnaruwa and Hambantota. It is also found in patches in the low country wet zone. It is frequently found along the banks of irrigation channels and agricultural land in the dry zone. In the wet zone it is mostly on roadsides, rail tracks and wastelands (Jayasinghe et al., 2004).
Dispersal and reproduction (pollination and seed dispersal):
C. campestris is mostly propagated by seeds, although local distribution takes place through vegetative spread. Wind plays a role in the distribution of cuscuta fruits but they are also dispersed by water as they are of a very low weight when dry and capable of floating. Dispersal through commercially important crops and seeds is highly possible since C. campestris seeds do not shatter from the capsules. They are harvested with the crop and are then difficult to separate.
Impact on native species and habitats:
The plant is most important as a pest of lucerne and other legumes. Grasses sometimes appear to be acting as hosts but are not normally penetrated. Crops commonly parasitized include a wide range of vegetables, soya beans, lentils and fruits.
Direct exploitation / destruction of native species:
The presence of C. campestris is always evident due to its sprouting stems and tendrils. Symptoms of damage are not especially characteristic, but reflect the very powerful sink effect for metabolites, causing a severe drain on host resources and often completely preventing normal seed and fruit development (Wolswinkel, 1979).
No control measures have been tested for this species in Sri Lanka. C. campestris has been tested and used as a control measure of another weed Mikania micrantha (Parker & Riches, 1993; Shen et al., 2005; Lian et al., 2006), however the success of this is doubtful and such implementation is not recommended for areas where M. micrantha infestation has not yet occurred.
Natural threats (pest/predators):
None recorded from Sri Lanka. A number of gall-forming Smicronyx species have been of interest as possible bio-control agents. Smicronyx jungermanniae and Smicronyx tartaricus are known to control C. campestris.
Prevention and control:
The young seedlings with rudimentary roots are readily destroyed by shallow tillage. Hand-pulling is suitable only for scattered infestations as the infested plants have to be removed with the parasite. Scattered infestations can also be controlled by heat, using a hand-held flame gun. A range of soil-acting herbicides are also effective in preventing the germination and establishment of this parasite.