Thursday, December 1, 2011

Green Algae Growing on the Trunks of Crepe Myrtles

Print this articleThe distinctive, attractive characteristics of crepe myrtle trees aren't so pretty when they're covered with substance that looks like green algae. Crepe myrtle, also known as crape myrtle and crapemyrtle, make beautiful ornamental trees when they're healthy. When the trees aren't healthy, they're a problem in landscapes. Identify and manage the problem that's causing algae-like growth and keep crepe myrtles healthy.

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Crepe myrtles are not immune to fungus. Powdery mildew may create growth on leaves and branches, but this fungus resembles white, powdery spots as the name suggests. Growths that resembles green algae on crepe myrtles are actually lichens. The easiest part of the lichen to recognize is the main body, which is largely comprised of fungus. Some lichens look like a crust, while others grow in leafy layers, but in all cases they are green and attach themselves directly to crepe myrtle trees.

Smarter Than Algae

Technically, lichens are not algae. Lichens are a fungus-like symbiotic organism. Like plants, lichens produce food for themselves through photosynthesis, absorbing sunlight to take in nutrients. The lichens give moisture to the plant upon which they grow. Because the unique relationship they have with the trees where they grow, lichens are something more than your average green algae, but they may not look it.

Lichen Damage

Lichens may change the appearance of crepe myrtles, but they are not damaging. Lichens do not fracture or harm bark, allowing pathogens and bacteria do harm the crepe myrtle. The lichens will cover and obscure the distinct bark on crepe myrtles, however, and for this reason many gardeners do not want the algae-like growth on their trees.


Because lichens do not damage crepe myrtle, removal is not necessary. Gardeners who do want to remove lichens to improve the look of the tree can scrub the algae-like growth off the trees with a wet scrub brush. Alternately, they can cover the lichen growth with a shade cloth and eventually it will die.

ReferencesOhio State University Extension; 10 Things You Should Know About Lichens; David J. Goerig, et al.Clemson University Cooperative Extension Service; Crape Myrtle Diseases & Insect Pests; Nancy Doubrava, et al.Royal New Zealand Institute of Horticulture : Moss and LichenResources"Southern Living" Magazine: Beginner's Guide to Crepe MyrtlesUniversity of Florida, IFAS Cooperative Extension Service; Crapemyrtle in Florida; Gary W. KnoxNC State University Extension; Crapemyrtle Problems; Erv EvansRead Next:

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