Black Dots on the Leaves of Birch Trees

Fungal Leaf Disease

• The leaves of a birch tree and most other hardwoods are susceptible to a wide number of fungal leaf diseases that produce black spots on the foliage. Most of these are active from June through August and display as round, angular or irregularly shaped spots with a dark brown or black color. These diseases typically spring to life and are most easily transmitted during periods of warm, wet weather as splashing rainwater and high humidity enable transfer of the fungi to leaves and adjacent plants.

Types

• The names of these leaf diseases vary widely according to their specific fungal origin and the exact forms of damage they cause. The names of fungal diseases that cause black dots on the leaves of birch trees include anthracnose, black spot, leaf blister, scab, shot-hole and tar spot. The black spots may be raised or smooth, dull or shiny and sometimes surrounded by a border or halo of different colors ranging from purple to yellow or red.

Symptoms

• In some cases, the black spots gradually become larger, merging to cover the entire birch leaf. In others, the black spots may simply kill the tissue and fall away, a symptom of shot-hole disease, a fungal disorder that leaves behind a collection of foliage that appears as if it has been riddled with gunshots. Depending on the specific fungus, tiny black fruiting bodies, the spores of the disease that then spread through wind and rain, may form within the center of the black spots.

Damage

• Another fungal disease known as black sooty mold afflicts birch leaves when insects leave behind honeydew -- sticky excrement -- that attracts a fungus that covers the leaves with a black, sooty powder. Most of the black spots on a birch leaf cause primarily aesthetic damage, but they can force the tree to prematurely defoliate and lose overall vigor. This is especially true if the disease continually attacks the tree over a period of successive years.