There have been several public enquiries lately about how to manage parasitic plants: dodder and mistletoes.
These plants are common around Anglesea and Aireys Inlet and there are several species of each.
Mistletoes are usually tear shaped, dense and hanging from outer branches with leaves often resembling host leaves, while dodder can be a small or large tangled mass of cylindrical vines.
Coarse Dodder-laurel Photo by John Lenagan
Coarse Dodder-laurel - detail of how climber tendril attaches to branch Photo by John Lenagan
Mistletoes are now referred to as ‘hemi-parasites’, meaning they photosynthesise and produce all their own energy, taking from their host only water and minerals. Healthy trees benefit from having a small number of mistletoes living on them. In return for the water and minerals, the tree receives regular visitation by hundreds of birds annually, which help keep it free from insect infestations. Mistletoes can be found on many different plant species, especially eucalypts and acacias.
Drawing by Mary White
Drawing by Mary White
Coarse Dodder-laurel, Cassytha melantha, can grow robustly and kill its host tree (often a messmate eucalypt or swamp gum but it could be any shrub).
In a natural environment the loss of a tree to dodder creates a clearing where other small plants can flourish until another tree regrows, but in a home garden, consideration should be given to removal as the small plants could be weeds and there will be limited opportunity for the tree species to return. However, to remove it, all infected branches must be removed, and in heavy infestations this may lead to the death of the tree.
There are several examples of dodder growing vigorously on eucalypts in Anglesea streets. Because dodder can kill host plants it is being investigated as a potential suppressor of weeds such as gorse and blackberry. While it may kill the odd tree, the tangled mass of vegetation certainly provides different ecological niches to most other vegetation types. Dodder species are more common than mistletoe in this district.
These ‘parasitic’ types of plants are natural features of our local vegetation communities and contribute to biodiversity values providing safe harbour, food and nesting sites for fauna. For example, I have witnessed many nests and ringtail possum dreys in dodder, Gang-gang Cockatoos and currawongs feeding on dodder fruit and numerous honeyeater species feeding on mistletoe flowers.
Mistletoes contribute to soil fertility when they are damaged and fall to the ground whereas many gum tree leaves are almost devoid of nutritive value before they drop. They also provide food for insects, fungi, birds, possums/gliders etc. Mistletoebirds rely on mistletoe plants for nesting sites and food. The fruit is eaten and the sticky seed is deposited on branches following digestion. I have witnessed this happening on a mulga tree at Alice Springs! Dodder fruit (drupes) are also spread by birds and animals.
In farming landscapes where the native vegetation has been reduced to scattered trees with no understorey, mistletoe infestations can kill the trees. Within large patches of bushland however, mistletoe is kept in check by natural predators and fewer trees experience stress. Tips for reducing the spread of mistletoe include supporting natural predators such as gliders and possums by providing nest boxes, where natural hollows are not available. In farming situations remove livestock which compact the soil around trees and lower tree health and reinstate the natural understorey.
Flowers of Anglesea and Aireys Inlet, 2009 Margaret MacDonald
Neil Marriot article in Upper Hopkins LMG Newsletter Summer 2017
Land for Wildlife Newsletter, Summer 2017/2018