Cuscuta monogyna
(eastern dodder)

Cuscuta monogyna is an aerial hemiparasitic plant native to the Mediterranean and temperate regions in Europe, Central Western Asia and North Africa. It has been introduced in Malta and Lebanon. There is no evidence of any impacts on natural habitat or biodiversity in these countries. It is considered invasive in Tajikistan, but the report did not differentiate between local and alien invasives. In its native range, C. monogyna is considered a weed species affecting crops in Ukraine and Russia, where it is included in the National List of Regulated Pests as a quarantine pest.

Cuscuta monogyna is native to the Mediterranean, Central, Southern, Northwestern and Eastern Europe and Central and Western Asia, as well as the Northern Caucasus, Trans-Caucasus and North Africa (Flora of China Editorial Committee, 2019; World Flora Online, 2019). It has been introduced in Malta and Lebanon (von Raab-Straube, 2018). It is considered invasive in Tajikistan, but the report did not differentiate between local and alien invasives (CBD, 2020).

Cuscuta spp. are subject to the strict quarantine regulations now in place in most countries (Holm et al., 1997), which should ensure that there is little risk of introduction.

Cuscuta monogyna is mainly associated with floodplains, forests and shrubs and steppe habitat in Eastern Europe (Fedorov, 2001). It is found growing on agricultural land (Fedorov, 2001; Nowak et al., 2014).

Cuscuta monogyna is included in the National List of Regulated Pests as a quarantine pest present locally in crops in Ukraine (EPPO, 2014). It is also included in the list of quarantine pests in the Russian Federation (EPPO, 2009) and is of significance for vineyard crops (Fedorov, 2001). It is found growing in cereal crops in Tajikistan (Nowak et al., 2014), but no further information exists about its agricultural impact.

Genetics

Cuscuta spp. belong to subgenus Monogyna and have extremely large nuclear genomes (McNeal et al., 2007). The chromosome number of C. monogyna is 2n=28 (Fedorov, 2001).

Reproductive Biology

The flowers are actinomorphic hermaphrodites only, with homogeneous seeds and fruits (Danin and Fragman-Sapir, 2016). C. monogyna flowers need insects for fertilization and pollination (Nazari and Tavakoli, 1995). Most Cuscuta species readily produce massive quantities of seed (McNeal et al., 2007).

Physiology and Phenology

Flowering times are variable depending on climatic condition. In Israel flowering is from May to September (Danin and Fragman-Sapir, 2016) and in Malta from February to April (Mifsud, 2020). The seeds are mature between in the middle to the end of summer. Numerous seeds are produced and can form soil seed banks; large numbers (each filament mass is about 1500 seeds and for a whole plant about 3000 seeds) with high viability are produced and remain on the ground until germination starts in the next season (Nazari and Tavakoli, 1995).

The seeds can remain dormant in soil for many years, for some Cuscuta species this can be for more than 20 years (Baskin and Baskin, 2014). Seeds of C.monogyna appear to have a relatively high temperature requirement of 30-33°C for maximum germination (Baskin and Baskin, 2014), but the most appropriate temperature for germination is 10-25°C. Sunny conditions are required and the seed should be buried in the soil at a depth of 3-7 cm. Germination is low in the first year (Nazari and Tavakoli, 1995). Once germination has started, the radical of the embryo develops into a root, which absorbs water from the soil; and the embryonic shoot bud is able to spend several weeks without a host. Thin and whitish filaments come out from the seeds, which start to attach to the understory grasses, becoming brownish in colour. Growth of the filaments reduces from the middle of September and stops completely in December. The filaments become dry and black and disappear in winter (Nazari and Tavakoli, 1995).

Nearly all species of Cuscuta retain some photosynthetic ability, especially as seedlings and in maturing fruits (McNeal et al., 2007). They contain trace amounts of chlorophyll and there is no RUBISCO activity (van der Kooij et al., 2000; Těšitel, 2016). Cuscuta spp. have no roots at maturity and their leaves are reduced to minute scales; their vegetative portion appears to be a stem only; and they live as stem holoparasites on other plants (Jones, 2018). The adult plants need a host as a source of nutrients and have a special adhesion/absorption organ called the haustorium, which is able to penetrate into the vascular system of the stems, leaves or roots of the hosts. (McNeal et al., 2007; Kaštier et al., 2018). It is observed that the cytoskeleton in dodder shoot cells is organized in a similar way to non-parasitic dicots, while in the quickly senescing root-like structure and prehaustorium the cytoskeletal organization has some peculiarities (Kaštier et al., 2018).

Associations

Cuscuta spp. are parasitic plants that are are reported around the world with different host ranges, cultivated or not (Hull, 2002). The natural hosts of Cuscuta are mainly dicotyledonous plants from Brassicaceae, Leguminosae, Solanaceae and other taxa (García et al., 2014). Some Cuscuta species are host specific (Abaye, 2019), but C. monogyna is a generalist with broad host ranges, mostly bushes and even trees (Kaštier et al., 2018), as well as grasses and vines (Vitis, Rubus, Pistacia, Laurus, Olea, Viburnum, Salix, Jasminum, Tamarix, Berberis, Syringa, Cytisus, Cotinus, Clematis, Paliurus, Punica, Ricinus, etc.). Other recent hosts are Glycyrrhiza glabra in Armenia (Piwowarczyk et al., 2018); Ficus carica in the Crimean Peninsula (Krasylenko and Piwowarczyk, 2019); and the oak tree, Quercus persica [Quercus brantii], which extends from Eastern and Western Azerbaijan to Southwestern Iran (Nazari and Tavakoli, 1995). Occasionally, hosts are other plants, such as Alhagi, Artemisia, Salsola, Cardaria, Phragmites (Piwowarczyk et al., 2018). In the Iberian Peninsula, it is a parasite of trees and shrubs of different species (e.g. Retama sphaerocarpa, Dittrichia viscosa and Tamarix (Garcia, 2012).

Environmental Requirements

Cuscutamonogyna occurs in a wide range of climates, temperate and subtropical and soils and has some tolerance of saline conditions (Dubyna et al., 1995). In Iran, it grows from 1250-2200 m above sea level (Nazari and Tavakoli, 1995) and from 300-800 m altitude in the Iberian Peninsula (Garcia, 2012).

It has been observed that the larvae of Eupithecia barteli, a moth in the family Geometridae, have been found in the ripening seed balls of C. monogyna in Kyrgyzstan and southern Kazakhstan (Mironov and Galsworthy, 2013). For further information on natural enemies of Cuscuta spp., including C. monogyna, see reviews by CAB International (1987).

General

• Laboratory use

The identification of species within Cuscuta can be problematic due to the loss of vegetative organs and the reduced sizes of structures with relevance for taxonomic purposes (McNeal et al., 2007). C. monogyna can be distinguished from other Cuscuta spp. because of the presence of a single style in the gynoecium and seeds that are 2.8-3.6 mm long (Garcia, 2012).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Parasitic weeds are controlled through an integrated approach, employing a variety of measures in a concerted manner, starting with containment and sanitation, direct and indirect measures to prevent the damage caused by the parasites and, finally, eradicating the parasite seedbank in the soil (Saric-Krsmanovic et al., 2017).

Thus, various methods are used (or have been used) in attempts to control Cuscuta in crops, including burning portions of fields that are badly infested in order to destroy the seeds, solarization, biological control and an integration of crop rotation and prevention of Cuscuta seed production (Baskin and Baskin, 2014), plus prevention of movement of livestock (Nazari and Tavakoli, 1995).

SPS Measures

Cuscuta spp. are declared Class 1 Prohibited Noxious Weed Seed in Canada (Government of Canada, 2016) and a noxious weed in 25 other countries (Holm et al., 1997), given the risk of it being introduced as a contaminant of crop seeds.

Chemical control

Pre-emergence and post-emergence herbicides can be used (Baskin and Baskin, 2014). No herbicide gives fully reliable control and the only option is the removal of the parasitic plants together with host in order to prevent spread and seeding (Parker, 2012).

Biological Control

Alternaria destruens strain 059 is a fungus that is parasitic to the more common Cuscuta species, but has not been tested on C. monogyna. It does not pose any risk to humans and other non-target species (Bailey, 2014).

Risk assessments for C. monogyna are necessary in order to determine the risk of its introduction and associated invasiveness.

06/05/20 Original text by:

Manuel Angel Duenas-Lopez, Consultant, UK