Is it a weed or not a weed?
Dodder is a common name attributed to many plants. The two genus in Tasmania commonly called Dodder are Cuscuta species’ (true Dodder) and Cassytha species’ (Dodder-laurel). They are not easy to tell apart, and they are not all weeds. When fruit and flowers are absent in the field, the physical resemblance is so close that few people without technical training can tell them apart.
The entire Dodder genus Cuscuta is a declared weed in Tasmania under the Weed Management Act 1999; except for the native Tasmanian species C. tasmanica, which is excluded from this declaration.
C. tasmanica is rare and endangered and occurs on the fringes of salt marshes and is not a weed.
Other Cuscuta species are introduced and are a serious weed of lucerne, clover and many other agricultural crops. Fortunately, the distribution of dodders in Tasmania is limited. Cuscuta suaveolens was found in a red clover seed-crop at Forth but has since been eradicated and is under surveillance. Another dodder (Cuscuta epithymum or C. campestris) has been recorded in the south of Tasmania. As of March 2020, the only municipalities they have been recorded in are Derwent and Huon Valleys and Devonport.
Cassytha is also parasitic vine which is often seen covering shrubs and trees in native bushland. It is widespread throughout Tasmania. This is not a weed. In fact it forms an important part of the natural ecosystem, with their fruits providing important food sources for some bird species. Possibly four species of Cassytha are found in Tasmania; C. glabella, C. melantha, C. pedicellosa and C. pubescens.
Cassytha species – Found throughout much of Tasmania in native bushland. If in native bush it is probably safe to assume it is native.
Cuscuta tasmania – Restricted to the fringes of saltmarshes. Threatened species, not a weed. The prostrate stems forming an orange splatter on the ground are distinctive.
Weedy Cuscuta species’ – Found in agricultural crops. Currently only been recorded in Derwent and Huon Valleys and Devonport municipalities. If you find it in your crop, it is wise to assume it is a weedy Cuscuta and report it to Biosecurity and take measures to eradicate it.
Growth Habit: Cuscuta and Cassytha are perennial parasitic vines that have thread-like stems that are green to yellow. It has no leaves. It attaches itself to a host plant through suckers. It produces a mass of stems in the canopy of the tree, eventually overcrowding the tree and killing it.
Flowers: The flowers are small and occur in dense clusters. Cassytha flowers have 6 petals/sepals (3 inner and 3 outer) and Cuscuta has 4-5.
Fruit/Seed: Small pea sized green berries ripen to red, then release several sticky seeds. Cuscuta fruit take the same color as the vine.
Dispersal: Birds eat the sticky ripe fruits, later passing the seeds in other trees. Cuscuta can also spread by stem fragments.
Cuscuta Weed Impact:
- Parasitic plant that sucks nutrients out of host crop species.
- Smothers crops causing them to die.
For further information contact the Department of Primary Industry, Parks, Water and Environment, Tasmania.
Cuscuta Control Methods:
- As they are not widespread, but have the capacity to significantly impact agriculture, early detection and prevention is important.
- The best way to control Dodder is to avoid the problem by planting only clean seed which is free of the weed.
- Small infestation of dodder can be controlled by removing all plants or portions of plants infected by dodder.
- Ensure all fragments of dodder are removed and destroyed as stem fragments can regenerate if they come in contact with a new host plant.
- Remove the weed before the dodder flowers and produces seed.
- Dodder seedlings are difficult to find, but if they are observed before they attach to a host, remove them by cultivation or by hand-pulling.
- For larger infestations in agricultural crops, the dodder plus host plants should be destroyed, for example by spraying with a flammable material (such as diesel), burning the crop plus weed and then cultivating the site.
- Re-sow to resistant crops such as cereals or pasture grasses, and do not re-sow to susceptible crops for at least five years.
- Chemical control – For information on chemical control options for dodder contact Biosecurity Tasmania on 03 6165 3777.
N.B. Always check the herbicide label before use.