Why Are My Birch Trees Sticky?

Sap Bleeding

• Birches can become sticky when the sap bleeds out. Excessive bleeding is often due to improper pruning, which can lead to a gooey mess down the trunk. In these instances, commercial paint pruners are ineffective and will fail to even slow the bleeding. While birches seldom need pruning, when it is necessary, prune in late spring only after the leaves reach their full size; pruning any earlier will lead to excessive sap leakage. This bleeding is not only sticky, but it causes the tree to lose water and sugar. Similarly, do not prune in late summer. While the tree will not immediately bleed, it is slow to recover from wounds, and cuts not fully healed will bleed as soon as the sap begins to flow again in the spring.

Honeydew

• Birches are susceptible to aphids, which are small, soft-bodied insects that feed on leaves by inserting a syringe-like mouthpart to suck out the leaf sap. They are highly reproductive and can quickly cover a tree. When aphids feed, they leave behind a sticky substance called honeydew. This then attracts ants and wasps and provides the environment necessary for the harmless black fungus commonly known as sooty mold to grow. Aphids often cause leaf distortion or some leaf loss in birches, but they do not usually cause serious or permanent damage.

Cankers

• Cankers are dead areas on tree bark caused by fungi, which often form reproductive structures to spread. They typically invade through wounded or diseased tissue, and their destructive abilities range from relatively harmless to a considerable threat to the tree's health -- even sloughing off the outer layers of bark to expose the sapwood. Once this sapwood is exposed, the tree is vulnerable to a variety of infections and invaders. In some cases, these cankers -- like the cytospora canker, which affects birches --ooze sticky liquid.

What To Do

• Proper tree care is essential in preventing problems. Prune the tree properly and at the right time. If your birch is oozing sap, keep it well-watered and don't bother with pruning paints. They won't work. Improper pruning can lead to infections, like the fungi that cause cankers. If cankers occur, diligently maintain sanitation and monitor the tree's health. Remove infected branches and dead bark and clean the canker wounds to deter further disease. To control aphid numbers, release populations of their natural predators, often available at gardening stores, into infected trees. Ladybugs are an excellent choice for this; they will not harm the tree and will feast on the bugs.