Tree Lichen

Asked September 5, 2019, 5:00 PM EDT

Hi, I have read that tree lichen will not harm trees. However, I have some shrubs that seem to be affected. I believe tree lichen killed off one of 11 Pinky Winky Hydrangeas last summer (over a couple of years of some branches dying off) and appears to be on some of the others. Nearby, are Cranberry bush 'Alfredo' viburnum trilobum and Arrowood 'Blue Muffin' viburnum dentatum that appear to have some tree lichen. I have started to spray what I can see with a stream of water from a hose. Is that the best thing I can use or am I harming the shrubs? Thanks, Fred

Eaton County Michigan

1 Response

Hello,

Yes, lichens are harmless to trees and shrubs, and no treatment or removal is necessary. They are using the bark as a secure place to grow, and they can do the same on dead wood and rocks or even cement. Wetting the branches actually gives the lichens a drink of water, and will help them grow. Here is information from Rutgers University Extension-

“Lichens are often found on tree trunks, branches and twigs as the bark provides a stable place to reside to collect needed sunlight, rainwater and materials from the air. They grow on healthy trees, as well as stressed or otherwise unhealthy ones. The appearance of colorful organisms growing on the bark of trees or shrubs in the landscape sometimes causes concern for the homeowner. Homeowners may find lichens mysterious and incorrectly associate them as the cause of plant diseases or misidentify them as a type of moss.

Many lichens are more evident on stressed or old tree trunks and branches giving the appearance of a "cause and effect" association with disease and decay. The primary reason for their more likely presence on those trees and branches with reduced or partial foliation is the resulting increase in available sunlight. The bark of a healthy tree continues to expand and slough off with the growth of the tree. The bark of an older or stressed tree may become more brittle with more cracks and uneven surfaces permitting lichens to attach themselves more readily. As bark ages, it changes in chemistry, texture, and ability to retain water, thereby influencing the type of lichen capable of living there.”

These links have complete details-

https://njaes.rutgers.edu/fs1205/

https://www.canr.msu.edu/news/lichens_a_partnership_in_nature_that_survives_in_diverse_environments

We may be able to help you determine why your viburnum seems to be declining. If you would, please attach a picture of the whole shrub, a close up of a problem branch with leaves, and a picture of the base of the shrub where it enters the soil. Also include some info on how much sun they receive, what your soil is like, how you give them water, and any fertilizer or other chemicals used.

I will watch for your pictures. Thanks for using our service.