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Plantwise Technical Factsheet

European dodder (Cuscuta europaea)

Host plants / species affected
Aegopodium podagraria (ground elder (UK))
Allium cepa (onion)
Alnus (alders)
Artemisia vulgaris (mugwort)
Astragalus stipulatus
Beta vulgaris (beetroot)
Crataegus monogyna (hawthorn)
Humulus lupulus (hop)
Mentha (mints)
Rubus idaeus (raspberry)
Salix (willows)
Urtica dioica (stinging nettle)
Vicia faba (faba bean)
Vicia sativa (common vetch)
Description
Cuscuta species are obligate parasites with negligible chlorophyll and leaves reduced to minute scales on a glabrous stem which twines around the shoots and leaves of suitable host plants. In C. europaea the stems are yellowish, orange or reddish, filiform, about 1 mm in diameter. Inflorescences are lateral, compact clusters, about 10 mm diameter, of few to many flowers each on pedicels up to 1.5 mm. Calyx cup-shaped with 4 or 5 sepals, triangular ovate, obtuse, about 1.5 mm long. Corolla of 4 or 5 triangular-ovate lobes, pink, 2.5-3 mm long, often reflexed. Stamens have filaments longer than the ovate-circular anthers. Scales very thin obovate, 2-cleft or entire. Styles 2 with filiform divergent stigmas about as long as the styles. Mature capsule capped by the withered corolla, sub-globose, about 3 mm in diameter, circumscissile. Seeds usually 4, pale brown, elliptic, about 1 mm, scabrous (from Fang Rhui-cheng et al., 1995).

Fritsche et al. (1958) provide detailed descriptions of the anatomy and morphology of C. europaea.
Prevention and control
Cultural Control

Use of clean crop seed is vital. Seed crops which might have been infested should be inspected and cleaned if necessary, or seed should be obtained from a source known to be reliable. Separation of Cuscuta seeds from lucerne is quite successfully achieved by equipment comprising felt- or velvet-covered rollers to which the rough seeds of Cuscuta stick while the smoother crop seeds pass over (see Dawson et al., 1994).

Rotation with non-susceptible crops can be helpful. Cereals are virtually immune, but some broad-leaved crops may also be sufficiently resistant, including soyabean, kidney bean (Phaseolus vulgaris), squash (Cucurbita sp.), cucumber and cotton (see Parker and Riches, 1993).

Deep shade suppresses the coiling and attachment of Cuscuta; hence encouraging a dense crop canopy is a valuable component of any integrated control programme.

Mechanical Control

The young seedlings of Cuscuta, with rudimentary roots, 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 of C. campestris have also been controlled by heat, using a hand-held flame gun. More extensive infestations of that species 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.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Integrated Control

Integrated methods for control of Cuscuta species generally involve the all-important use of clean seed; good field hygiene to eradicate scattered infestations before they get out of control; good control of other weeds which might act as reservoirs of infestation; timing of tillage and planting to maximize destruction of parasite seedlings before sowing; and optimum planting arrangement and growing conditions for a good crop canopy to suppress development of the weed.
Impact
Holm et al. (1979) list C. europaea as a 'serious' weed in Afghanistan and Poland, and a 'principal' weed in Czechoslovakia and the former USSR. It is rarely a major weed over large areas, perhaps because of the lack of attack on Gramineae [Poaceae], and the cleaning effect of cereal crops in rotation. But once contact is established with the host phloem, Cuscuta becomes a powerful sink for metabolites, causing a severe drain on host resources and often completely preventing normal fruit development, as shown by Wolswinkel (1979) for C. europaea on faba bean (Vicia faba). Owing to this powerful metabolic sink effect, studied and described in detail by Wolswinkel and Ammerlaan (1983), the damage to infected hosts can be severe, to the extent of total crop loss. Less dry matter and ash were found in the leaves of parasitized Urtica dioica and Aegopodium podagraria than in those of healthy plants. Leaves of parasitized U. dioica plants contained 8.5% less chlorophyll than uninfested ones (Gal'vidis, 1993). Perhaps the crop most seriously affected is sugarbeet in Italy, the former Yugoslavia and eastern Europe. There is also further economic loss when crop produce, such as clover or lucerne seed, intended for export, is rejected or has to be expensively cleaned.

There are occasional reports of toxicity to livestock from Cuscuta species, including toxicity to horses from C. europaea (Pergat and Stolyarova, 1961).
Summary of invasiveness
C. europaea has not proved to be a highly invasive species, but there are very significant risks of accidental introduction with contaminated crop seed and any such introduction could cause serious crop damage, and prejudice options for trading crop produce.
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