If you’ve noticed a frilly, greenish-gray growth on your tree’s bark, it may have lichen. Many people blame this organism for a tree’s failing health, but lichen is not a parasite and merely affects your tree’s appearance. You can treat trees with lichen manually and chemically.
What Is Lichen on Trees?
Lichens may look like moss, but they differ in that they have a mycobiont and a photobiont living in symbiosis. Mycobionts include fungi, while photobionts can be algae or cyanobacteria. Photobionts photosynthesize to obtain nutrients, meaning that lichens do not affect a tree’s health. You can find them growing on nutrient-free rocks as well.
Wind spreads lichens by blowing their reproductive structures around. These lightweight organisms can settle on any still object, like a brick wall, tree, or rock. They prefer slow-growing trees like oaks because their surfaces take a long time to change.
People associate lichen with the failing health of trees because it often appears on stressed plants. These trees may become stressed from insufficient moisture, sunlight, soil, planting depth, or insect infestation. Lichens can appear on trees of any health level, but they become more apparent on ones that look sick.
What Damage Does Lichen on Trees Cause?
Lichens do little damage to trees alone; however, they can spread to the tree’s leaves and interfere with its photosynthesis.
If the lichens grow too thick, they can weigh down a tree’s branches or stems and cause them to break. Nevertheless, lichen is not a parasite, so it is completely safe and even beneficial in small amounts.
Lichen on trees can house beneficial lacewing larvae. These critters eat dangerous pests and camouflage themselves in lichens. Some small animals and birds use lichen for their nests.
How to Control Lichen on Trees
You can remove lichen manually with potassium spray, baking soda, or copper sulfate. The chemical methods may harm the tree, so try to remove them by hand first.
Manual Extraction
Manual extraction is the safest way to remove lichen. You will need a wooden or plastic scraper that isn’t so hard that it will harm the tree, but it can still scrape off the lichens. Try to scrape the tree bark gently to remove the lichens.
You will likely see healthy bark under the lichen once you have removed the excess vegetation. The best time of year to manually extract lichens is in spring or when the tree is dormant as they will separate easily, and the trunk can heal faster.
The best type of lichens to remove manually hang from the branches and have a hair- or moss-like look. If they appear loose enough, you can lift them off by hand. Make sure to do it gently without jerking the tree to prevent damage.
Potassium Spray
Another relatively safe way to remove lichens from trees involves spraying them with potassium. This element is a contact killer that will eliminate the lichens soon after spraying.
All of the sprayed lichens should die within a few days, and some trees will clear within a few hours. Since potassium is a root fertilizer, it will not harm your tree. Any excess may fall to the roots and benefit your plant.
Keep in mind that some commercial potassium sprays may damage your tree as the manufacturers designed them for patio use. Make sure to check the usages and try to get the purest product possible to avoid pollution.
Baking Soda
The safest chemical solution to treat trees with lichen is baking soda. This treatment is high in salt, so you should not use it on trees with new growth. Baking soda is another powerful contact killer. Before spraying your plants with baking soda, try to remove as much lichen as possible manually and use it sparingly.
Copper Sulfate
The final lichen treatment is the most dangerous. Copper is an antifungal treatment employed in many dry fertilizers.
This systemic spray takes the most time, but it should kill most lichen. While effective, copper sprays can damage tree growth. By spraying your trees late in their sprouting season or before the next one begins, you can prevent them from damage.
Check that the spray you buy works for plants. Most copper sulfate sprays will kill other bacterial and fungal diseases. When used correctly, they make an excellent addition to your plant care regimen.
Prevention
You can prevent lichen from growing on your tree by keeping it healthy. Make sure to provide your plant with enough sunlight, water, and fertilizer.
Try to grow it in its native soil type and prune it to maintain its appearance. While you cannot prevent the wind from blowing lichen onto your tree, you can minimize its appearance by keeping your tree healthy.
