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I Didn’t Know That!

By Lucinda Greene, Colorado Master Gardener

Is Your Tree Having a Bad Hair Day?

Photo: Lucinda Greene, Englewood, CO

On a recent spring day, I ventured outside in the yard to enjoy the sunshine. Imagine my surprise when I noticed some abnormal growths in my neighbor’s hackberry tree. The bare limbs showed snarls, the likes of which I haven’t seen since my daughter was a youngster and each shower made her hair a thick mess of tangled curls.

Aptly named “witches’ broom,” these small growths of numerous small twigs, or brooms develop on several species of trees, including oak, juniper and hackberry. On hackberry, two disease organisms must be present for the symptom to occur: the fungus causing powdery mildew or Sphaerotheca phytophila and Eriophyes celtis, one species of the Eriophyid mite. When the disease is identified, powdery mildew fungus is found on stems and buds in early spring and the mites are found overwintering beneath the bud scales. In most cases, the disease is an aesthetic concern rather than being harmful to the tree. However, affected twigs or branches can break more easily and therefore expose wood to additional disease or decay. Pruning any diseased twigs or branches to sound wood can improve the tree’s appearance and help control the spread of the disease. A thorough fall clean-up of leaves and debris, especially in irrigated landscape situations, can help reduce the spread of powdery mildew and Eriophyid mites which are contributors to the disease.

Have you noticed something new in your landscape that you have a question about?  Master Gardener volunteers are on duty Monday through Saturday to answer your gardening questions.  You may reach us at 303-730-1920 or at mastergardener@arapahoegov.com.

W. Cranshaw, D. Leatherman, B. Jacobi, and N. Tisserat, Insects and Diseases of Woody Plants, Colorado State University Extension, Colorado State University Bulletin #506A, 2014.

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