Cuscuta species have a very distinct appearance, consisting mainly of leafless, glabrous, yellow or orange twining stems and tendrils, bearing inconspicuous scales in the place of leaves. In C. campestris, the yellow to pale orange true stems, about 0.3 mm in diameter, generally do not twine and attach to the host, but produce tendrils of similar appearance, arising opposite the scale leaves, which do form coils and haustoria (Dawson, 1984). The seedling has only a rudimentary root for anchorage, while the shoot circumnutates, i.e. swings round anti-clockwise about once per hour, until it makes contact with any stem or leaf, round which it will coil before growing on to make further contacts. The root and shoot below this initial attachment soon die, leaving no direct contact with the soil. Haustoria form on the inside of the coils and penetrate to the vascular bundles of susceptible hosts. Flowers, each about 2 mm across, occur in compact clusters 1-2 cm across. There is a calyx of 5 fused sepals with obtuse or somewhat acute lobes, and 5 corolla lobes, triangular, acute, often turned up at the end, equalling the length of the tube. Stamens alternate with the corolla lobes, each with a fringed scale below. The ovary is almost spherical with a pair of styles with globose tips. The capsule reaches 2-3 mm across when mature, with a depression between the two styles. The capsule does not dehisce and seeds remain on the plant long after maturity. Seeds are irregular in shape, rough-surfaced, about 1 mm across.
Related invasive species
- Cuscuta campestris
Related Farm Practice
- Soil
- Damage
- Development
- Hosts
The parasitic weed C. campestris is native to North America but has been introduced around the world and become a weed in many countries. It is by far the most important of the dodders, perhaps because of its wide host range. This ensures that there is a wide range of crop seeds that may be contaminated, and in which it may be introduced to new areas over both short and long distances. Once introduced it is almost certain that there will be suitable host plants on which it can thrive and be damaging, whether they are crops or wild species. Vegetative spread can be very rapid – up to 5 m in 2 months. It also has a wide tolerance of climatic conditions from warm temperate to sub-tropical and tropical.
The presence of Cuscuta is always obvious from the twining stems and tendrils. Symptoms of damage are not especially characteristic, but reflect the very powerful sink effect created by the haustoria, resulting in reduced vigour and, in particular, poor seed and fruit development.
The host range of C. campestris is extremely wide. Several hundred crop and weed species have been listed as hosts, though some of these may only be acting as secondary hosts after the parasite is established on a more favoured primary host (e.g. Gaertner, 1950;Kuijt, 1969). Most are dicotyledonous, though the monocot onion can be seriously attacked. 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. The literature on host range is usefully reviewed by Cooke and Black (1987). Crops commonly parasitized, other than those listed in the table, include asparagus, chickpea, lentil, grape, citrus, melon, Lespedeza and flower crops including chrysanthemum. Not all hosts are consistently attacked, for example tomato is susceptible when young but becomes resistant with age (Gaertner, 1950).