What to Use for Lichen on Crape Myrtle

Identification

• Generally, lichens appear like a dense, well adhered, green colored fungus growing on plant bark. Lichens also come in other colors including gray, brown or shades of red. Some lichens have a crust-like texture, some have leaf like filaments growing from their surface and certain other species have a fine and hairy growth. Regardless of color and form, all lichens are harmless to affected plants.

Biology

• Lichens are the result of a combination of an algae and a fungus that are mutually beneficial to each other as they grow on trunk and branch areas. Lichens, unlike parasites, are not harmful to the plant since they do not penetrate live tree tissues. The fungi and algae only use the plant surface for support and are just as commonly seen on non-living surfaces like logs, fences and rocks. While lichen themselves are not damaging they appear more frequently on poorly growing plants. For this reason, some experts like the New Mexico State University Extension do not advise any control strategies for lichens.

Chemical Control

• If you do want to control the growth of lichens on your crape myrtle trees, the Alabama Cooperative Extension recommends the use of copper-based fungicides such as products containing copper hydroxide. Mix together 1 level tbsp. of chemical in a gallon of water and spray on affected plant areas. Repeat applications every one to two weeks. Copper-based fungicides are sold under different trade names.

Cultural Control

• The best way to make sure that crape myrtles remain free of lichens is to keep the plants in good health. Irrigate and fertilize the shrubs regularly as this reduces the effects of stress like drought and encourages healthy growth. Lichens are most attracted to plants with declining and poor health. Do not prune the shrubs excessively as the abundant sunshine in the inner areas promotes lichen growth. Lichens are also common on plants that are growing in polluted areas with high levels of ozone, acid rain or sulfur dioxide.