Why do sycamore maples lose their bark

Maple bark is peeling off: what to do if the tree loses the bark

Maples (Acer) form their own genus within the soap tree family (Sapindaceae). There are 110 to 200 species, depending on the classification. The maple is often confused with plane trees because of the similarity of the leaves. However, shedding the bark of plane trees is a natural process. If, on the other hand, the maple loses its bark, this is often a symptom of serious diseases in the tree that require immediate action. Because this is the only way to have a small chance of saving the tree.


Causes of Bark Flaking

When the maple's bark bursts, it is usually due to frost damage or a disease. Since the latter can also be harmful to human health, you should start looking for the causes immediately.

Bald frost

Although maple trees can withstand temperatures down to minus 40 degrees Celsius, freezing can cause the tree bark to burst. Bald frost occurs when dry cold is combined with intense exposure to the sun. This weather gnaws at the bark until it bursts. To help the tree, take the following measures:

  • Smooth out cracks or damaged areas on the bark tissue with a sharp knife and seal with wound closure
  • Put a thick layer of damp clay over the exposed cambium
  • Protect the wound with black foil until fresh bark has grown back

You can protect the tree with the following preventive measures so that freezing does not damage the tree:

  • Place wooden boards around the trunk
  • Cover the bark or trunk with reed mats
Tip: You can also help the tree with these measures if game browsing has resulted in the loss of the bark.


If, due to the weather, freezing can be ruled out as the cause of the maple bark bursting, then a fungal infection is usually responsible for the damage. The diseases that cause the bark to burst include:

  • the soot bark disease
  • the maple stem shrimp (fruit tree shrimp)
Tip: Both mushrooms can be present in the maple tree for years without triggering the corresponding diseases.

Soot Bark Disease

The causative agent of soot bark disease is a fungus by name Cryptostroma corticalewhose spores are harmful not only to the maple, but also to humans, since the spores can inflame the alveoli or trigger allergies. The fungal disease often occurs as a result of long and dry summers, which weaken the maple tree.

In the case of soot bark disease, the tree shows the following symptoms at the beginning:

  • Deformations of the bark
  • withered leaves
  • Leaf litter
  • Slime flow stains on the maple trunk
  • green or blue discolored torn areas

In the further course

  • the tree loses its bark over a large area
  • black, soot-like coating appears
  • Spores color the surroundings, e.g. the plants or the ground under the maple, black

Since the soot-like coating is below the tree bark in the early stages, you should be extremely careful when examining the maple so that you do not become infected with the fungal disease. If you do not have the appropriate protective equipment, it is advisable to have the tree examined by a specialist and to discuss how to proceed.

Tip: Since the soot bark disease poses a risk to humans, you must have the tree felled and disposed of properly.

Maple stem shrimp (fruit tree shrimp)

The fruit tree cancer is caused by the fungus Nectria galligena caused. With this fungal infection, the bark bursts and small, round structures grow out. Below the bark is located

  • a white surface in summer
  • orange in autumn, spheres the size of a pinhead

In both cases the tree tries to cover the infected areas with bark. In contrast to soot bark disease, maple stem cancer has a small chance of saving the tree if the symptoms are not yet clearly pronounced. The following measures have proven effective:

  • Remove affected branches immediately (characteristic: bark bursts and tree loses the first leaves)
  • Cut out diseased wood until it is healthy
  • disinfect
  • Treat the tree with biological fungicides
Tip: The fruit tree shrimp occurs in the home garden especially on old trees. You should therefore have the trees checked for stability if they are infected.