As fall gets underway, each leaf drop reveals more of your fruit tree’s elegant bark.
On closer inspection though, the dark-gray bark of your apple tree can be covered in patches of yellow or gray scales and leafy mats that look like a fungal disease.
Fortunately, this isn’t a disease — it’s lichen. But what is it doing there?
Lichen growth on apple trees can indicate stress due to neglect or poor environmental conditions, such as improper soil, persistent dampness, and incorrect planting location and depth. Lichen is usually more common on older trees with brittle cracked bark as lichen can attach itself more easily.
A mild covering of lichen itself will not cause direct harm to your apple tree. Rather, the presence of lichen is an indication that the tree isn’t in the best health.
To help combat this and understand lichen growth, keep reading. We’ll explain what this strange growth is, how to identify it, what causes it, and more.
If you want to spot trouble on your apple trees quickly and resolve issues as fast as possible, my detailed guide, Apple Tree Diseases and Pests is a must-read.
It can be hard to distinguish lichen from moss, algae, and other growths on trees, So first off, let’s explain what lichen is and the types of lichen you may find on your apple tree.
What Is Lichen?
Lichen is nonparasitic fungi that grow on bark, rock, and other hard surfaces, appearing in crusty gray, green, or yellow patches or as hanging leafy growth.
These plant-like organisms favor damp conditions but can thrive in places where water and nutrients are scarce.
Lichens are a combination of two different organisms: lichen fungi cells and green/blue algae or cyanobacteria.
According to the University of New Hampshire, lichen cannot produce its own food and so relies on the photosynthesis present in algae cells for energy.
In turn, lichen provides minerals and water to prevent the algae from drying out! This mutually beneficial system is known as symbiosis.
Common Types of Lichen Found on Apple Trees
The three main forms of lichen are crustose (covering the bark’s surface), foliose (leaf-like growth attached to the lower surface), and fruticose (which is shrub-like and attaches to the base of trees).
The latter two lichens are most commonly seen on apple trees, and these appear as large leafy growth such as the ‘Green Satin’ lichen species (Lobaria virens) and a brown-lobed species known as ‘Stinky Stictas’ lichen (Sticta spp.), which emits a fishy smell when wet.
Lichen and Apple Tree Health
While finding some crusty and potentially smelly fungi on your apple tree is not something to celebrate, lichen does not always spell doom for your tree.
Read on to understand a little more about lichen’s effect on the health of your apple tree and when to worry.
Impact of Lichen on Apple Tree Health
In small amounts, lichen will not harm your tree and can even be beneficial. It attracts helpful lacewing larvae, a bug that camouflages in the lichen and kills dangerous pests like aphids!
Small areas of lichen also lure squirrels that use it as a source of food and is used by birds and small animals to make nests.
As long as apple trees are growing at their correct rate, the lichen-covered bark layer will slough off to be replaced with new inner bark just as our skin does.
Trees that are not growing as expected, however, cannot shed their bark as easily, allowing the lichen to spread further.
Lichen only poses a problem when it’s allowed to colonize wide areas of the tree, such as bark, branches, and shoots.
Minimal, harmless lichen growth is often seen on older trees, but if lichen is allowed to grow on younger developing trees, this can dry out the branches and impact fruit production, indicating a poor growing environment.
Relationship Between Lichen and Tree Stress
Stressed trees tend to lose their foliage due to environmental factors or poor cultural practices.
This decline in their canopy invites more sunlight onto the tree, which then nourishes the lichen organism.
While a healthy tree can regularly slough off or shed this unwanted growth, highly stressed trees develop brittle bark with cracks and uneven surfaces, making it easier for lichens to attach and flourish.
Factors Contributing to Lichen Growth
Old age and stress influenced by certain care practices are the most likely reasons for lichen growth on your tree. Contributing factors include:
- Damp and shady locations – You may spot lichen growth on the side of tree trunks that face prevailing wind and rain. Shady areas of the trunk can also be a haven for gray or rusty-orange lichen.
- Neglected trees with overcrowded branches can attract lichen growth, especially in humid areas as crossing/rubbing branches can encourage disease, weakening the tree.
- Trees generally lacking in vigor for whatever reason (imbalanced watering, lack of light, low nutrient levels, etc.) or trees that have begun to die back, signaling distress.
Assessing Lichen Growth on Apple Trees
Lichen is typically gray or green but can also be yellow or orange and can form in crusty patches that appear pressed into the bark (crustose), leafy mat-like growth, or hanging growths (foliose and fruticose) on the bark and branches.
Lichens grow all year round but are noticed more during winter.
Lichen vs. Moss
Lichen is often confused with moss, but an easy tell is that moss has tiny leaves and stems because it is a plant, unlike lichen, which is a fungi-algae partnership.
Moss also has a denser texture, growing in matted tufts of yellowish-green or forming dense cushions.
Managing Lichen Growth
Identifying and correcting the stress factors is the best method for keeping lichen growth at bay on your apple tree.
In addition to cultural control, lichen can also be removed by hand or using chemical methods (as a last resort).
Cultural Practices To Discourage Lichen Growth
- Corrective pruning is encouraged to reduce crowding. Remove broken, crossing, or diseased/dead branches. This promotes better air circulation and reduces the damp conditions in which lichen thrives.
- Avoiding overhead watering that essentially “feeds” the lichen.
- Apply a balanced fertilizer like this one to reduce stress for the tree.
Chemical Methods for Lichen Control
In severe cases, copper-sulfate spray can be applied to kill the lichen fungus between early spring and late summer/early fall, but this won’t be effective in cooler weather.
Manual Removal Techniques
During winter, once your apple tree is dormant and can heal well, you can manually remove the lichen from the bark or branches by taking a wooden or plastic scraping tool to the growth and gently scarping until you can see healthy tree bark beneath.
Carefully scrubbing the lichen off with a natural soapy water solution can also be effective, but be sure the scrubbing is in small gentle motions to prevent injury.
Depending on the lichen type, you can sometimes simply lift it off the tree.
Maintaining Healthy Apple Trees
Providing great care gives your apple tree the best shot in deterring stress-related growth and ensuring long-term vitality overall.
Here are some top tips to keep your apple tree healthy:
- Plant in fertile, free-draining soil to prevent waterlogged conditions.
- Ensure the tree has enough space for its mature spread and is spaced at least 6 feet away from walls, fences, or other structures.
- Prune back problem branches each winter for increased airflow.
- Plant in a sunny, sheltered spot where it can receive 6-8 hours of full sun a day.
- Water new trees regularly for their first growing season (4-10 gallons each week), and provide a 2-3 inch layer of mulch around the base every spring to conserve moisture and suppress weeds.
- Rake up the lawn of fallen leaves and debris around your tree to reduce the chances of harboring damaging fungal spores or providing shelter for pests.
Is Lichen Harmful to Fruit Trees?
Lichen itself is not harmful to fruit trees, but the presence of lichen may signal decline and lack of vigor.
Large, widespread patches of lichen can block out air and sunlight and may attract pest infestations, but fruit trees can tolerate light amounts of lichen growth.
Does Vinegar Kill Lichen on Trees?
Yes, vinegar can be an effective natural method for killing lichen on trees.
Due to its corrosive nature, however, the acid in vinegar may damage healthy tree bark, so it’s advisable to consult an arborist before using vinegar on your fruit tree.
In small amounts, lichen growth is not a cause for concern and even brings beneficial critters to your garden!
However, an overgrowth of lichen can block out much-needed sunlight and air and indicate an underlying health issue.
Lichen is normal on aged mature trees that have naturally lost their vigor, but lichen on young trees is a sign that something in their care or environment needs to change, such as a better planting location or more regular pruning.
Lichen can be removed fairly easily, so take steps to maintain good care, and your apple tree shouldn’t be troubled by lichen.
The more familiar you are with apple tree problems, the better equipped you’ll be to manage issues as they arise. Learn about these apple tree diseases next: