Lichens not as bad for trees, shrubbery as thought

Posted 8/19/18

Among the many calls that we get at the Extension office is a fairly common complaint that my trees and or shrubs have a “crusty or mossy” growth on the limbs or bark that is killing my trees. These growths are actually lichens.

This item is available in full to subscribers.

Please log in to continue

Log in

Don't have an ID?

Print subscribers

If you're a print subscriber, but do not yet have an online account, click here to create one.


Click here to see your options for becoming a subscriber.

Lichens not as bad for trees, shrubbery as thought


Among the many calls that we get at the Extension office is a fairly common complaint that my trees and or shrubs have a “crusty or mossy” growth on the limbs or bark that is killing my trees. These growths are actually lichens.

Lichens are very often blamed by homeowners for the decline and even death of numerous shrubs as well as landscape and fruit trees in local landscapes. That isn’t too surprising because lichens are very frequently seen on limbs, branches, and bark of declining or dead shrubs. What is surprising to find out, however, is that the lichens are not actually killing or causing the affected trees or shrubs to decline.

Actually lichens rarely have anything to do with poor top growth or decline of trees and shrubs. Their appearance is actually more related to environmental stresses or poor management. Lichens can be thought of as a symptom and not a problem much the same way as a fever is a symptom of an infection.

Lichens are actually two organisms in one so to speak. They are made up of a type of fungus and a type of blue-green algae living in symbiosis. The algae part of the lichen uses photosynthesis to make food that the lichen lives off of while the fungus supplies water, minerals, and protection from any of several harmful environmental conditions.

There are three types (actually forms) of lichens commonly found in Walker County landscapes. Crustose form lichens form a flat grayish crust on the limb or branch, folicose form lichens produce leaf-like folds above the limb, and fruiticose lichen produce and almost “moss-like” appearance with hairy fingerlike branches. It is not uncommon to see a combination of two or all three forms all growing on the same tree.

As I said earlier, the lichens themselves are usually not the problem to be worried about. The important thing to be worried about is why the tree or shrub is under enough stress or has declined to the point that the lichens can grow on it. The one exception is that when lichens grow is extremely large numbers, they can interfere with some plant processes or can actually shade out buds causing further decline.

Healthy vigorous plants is the best defense against lichens. Heavy infestations of lichens are most common on shrubs and trees that are either declining or are under stress or are in poor general health. Following recommended establishment, watering, and fertility practices will help to promote the development of a thick leaf canopy which will inhibit lichen growth.

Better growing conditions and soil fertility may stimulate plant growth and ultimately suppress the lichens. Light pruning (at appropriate times of the year and not during the middle of a drought of course) will help to remove some lichens and stimulate new plant growth. The unfortunate thing is that many plants that develop lichens are already in such poor condition that it may be too late for improved cultural practices to do much good. These plants will probably end up having to be replaced. Again, the main reason is usually either environmental stresses such as poor soil conditions, drought, or sometimes even simple old age in the tree or shrub but not due to the lichens themselves.

The take home lesson here is do a good job planting (not to deep, not too shallow, and plant in a WIDE hole to allow plenty of root growth) and do a good job of watering, fertilizing, liming, and pruning. You will have much healthier plants and far fewer lichens.

Presently, no pesticides are even recommended for the control of lichens on trees and shrubs, and even if they were used a simple spray will not do anything to alleviate the underlying stress that is causing the plant to decline in the first place. We have a simple rule that we teach to our Master Gardeners that goes “Put the right plant in the right place” taking into account the amount of sun verses shade, drainage, dry site verses wet site, USDA climate zone the plant is comfortable in, and others. Always do a good job on planting trees and shrubs so that they get off to a good start, and don’t forget supplemental watering during dry spells.

Last xall For 2018 Master Gardener class

The Walker County Extension Office will be offering our 2018 Master Gardener Course beginning on Thursday, Aug. 30, and running for 12 consecutive weeks through Thursday, Nov. 15. Each class will be taught at the Extension Office auditorium from 10 a.m. until 3 p.m. Home vegetable production, home orchards, soils and fertilizers, native plants, annuals and perennials, plant propagation, weed control in home gardens and landscapes, plant diseases and insects, home turfgrass, and backyard wildlife are just a few of the topics which will be covered.

The registration fee is $125 which includes all class supplies, instruction, and a copy of the newly updated Master Gardener Handbook. We will be accepting registrations through Friday, Aug. 24, 2018.

If you are interested in participating in our Master Gardener Course, call us at the Walker County Extension Office at 205-221-3392 for more details and for assistance getting registered for the upcoming class.

Danny Cain is the county extension agent.