Strange growth on pine tree branches

Asked July 23, 2017, 4:28 PM EDT

We have a beautiful hedge line of mature pine trees about 20 feet tall. The bottom branches have slowly been infected by this white-ish growth. The trees branches are slowly dying and infecting others. What is it and how do I stop it (or treat it).
Thank you in advance.

New York County New York

1 Response

Your trees – Norway spruces – are hosting a composite organism called lichen (a combination of an algae and a fungus); these are important and generally beneficial organisms in nature. Lichens are slow-growing and long-lived, and often grow on tree trunks, branches, and twigs, because bark provides a stable place for them to reside and collect sunlight, rainwater, and materials from the air. On conifer or evergreen trees such as spruces, lichens tend to locate on branches that are stressed or dead because the scarcity of needles on these branches gives them better access to sunlight, which may give the erroneous impression that they have contributed to the plant’s decline.

As far as I can tell from the photos you posted, your trees are generally healthy, and the lichen is definitely not harming your trees, but it might be a signal that they are otherwise stressed by a disease or insect that is not visible in the photos, or simply that they are aging.

Interestingly, lichens are sensitive to air quality, so the presence of lichens on your trees may be a positive indicator of lower levels of air pollution and a reasonably good quality of atmospheric conditions in the neighborhood.

Here is more information about lichens: