So the trunk of your tree or shrub is covered in crusty green stuff – don’t panic! It’s unlikely that this ‘green stuff’ is harming the tree. What you are observing is the growth of lichen on the bark.

Lichens are non-parasitic organisms that consist of a partnership between a fungus and a green alga or cyanobacterium. The fungus collects water and minerals from the air and substrate and the alga/bacterium contributes photosynthates and other nutrients. The lichen itself grows on the surface of the organism or object (trees, rocks, dead wood, grave stones, etc.) without causing any harm or negative impact to its host.

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Leaf curl and leaf blister are a group of diseases caused by the fungus Taphrina. Taphrina caerulescens is the causal agent of oak leaf blister, and Taphrina deformans is the causal agent of peach leaf curl.

These diseases are common in spring as the pathogens infect newly growing leaves, flower parts and fruits. Only undifferentiated (still growing) tissues are susceptible. Therefore, most infections occur during or just after bud break. The disease is often more severe when weather is cool and wet. Once the plant tissue has matured, fungal spores that may be present throughout the growing season are not able to infect the host.

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