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The appearance of lichen on the branches of a tree is often accompanied by a slowing down in the growth of the plant. Is it a plant parasite? No not at all: if lichen develops, it is the sign of negligence by the gardener!
The symptoms
Lichens appear very progressively on branches. At the beginning, they form a small crust that is only a few millimetres wide. As the months and years pass, the crust gets bigger and spreads out covering the bark. The most common lichen forms a yellow crust but it is also common to see grey dishevelled lichen in old apple trees. If the location is very humid and the air not polluted, the lichen take on the form of small trees and less crust like forms.
Lifecycle
Lichen is a symbiosis, this means it is a cross between a fungus and an algae. It is not a parasitic plant like mistletoe. It requires a lot of humidity to keep it alive, just like moss. It is thus on the shady sides of branches that the conditions are most favourable, as well as on porous walls and damp stones. However, if lichen develops on the branches of a tree it is because the bark of the tree has become very lazy. A tree in top condition renews its bark regularly or grows every year. If it looses vigour, then it offers more favourable conditions to lichen that will install itself, little by little.
How to fight it
There is no need to fight against the lichen but rather against negligence. When lichen starts to develop on plants that have lost their vigour, you should be worried and strive to get them back on form! The appearance of lichen is often a sign that the tree needs pruning and better maintenance. It also develops on shrubs that are nearing the end of their life and that you should think about replacing. Lichen on the trunks of fruit trees provides a winter retreat for fruit pests and it is best to brush it off during a dry spell in winter. In this case, think also about cutting off any dead branches on the fruit trees.
How to avoid it
Only regular maintenance of shrubs through balanced pruning that lets light into the centre of the tree’s branches will help avoid the proliferation of lichen. Lichen can however be decorative and add colour to the bark of otherwise dull shrubs!
Good to know
In a garden that is, bursting with life there is a wide diversity of lichen. No lichen can cause harm to a plant in our latitudes. So why not take a keener interest in this microscopic world? It really is fascinating! - Photos (1)
Lichen
Lichen
Author: Jean-Michel Groult
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