On those decision-a-minute days when keeping your family, job or home on track seems overwhelming, a visit your crepe myrtles (Lagerstroemia spp.) can restore your equilibrium in the space of a toddler's timeout. Jewel toned, with late spring to fall blooms, brilliant fall foliage and exfoliating bark, crepe myrtles are year-round stunners. All they require in return are full sun, supplemental summer water, annual fertilizer and -- in less than ideal conditions -- treatment for white fungal diseases.
1. White Leaf Fungus
Where Japanese and Indian crepe myrtles (Lagerstroemia faurieri, Lagerstroemia indica) flourish in U.S. Department of Agriculture plant hardiness zones 6 or 7 through 9, dry late summer conditions and temperatures dropping into the 60- to 80-degree Fahrenheit range favor powdery mildew's development. You’ll recognize crepe myrtles’ most common disease from the powdered-sugar blotches on their leaves. Left untreated, it stunts the foliage and flower stems, prevents proper bud development and causes early leaf drop. Powdery mildew fungi typically target closely spaced crepe myrtles growing in excessive shade.
2. Managing Powdery Mildew
To discourage powdery mildew, remove new suckers sprouting from the base of crepe myrtles along with symptomatic leaves and twigs. Thin overhead branches to give the plants more sun. Safe measures for kids, pets and wildlife include spraying crepe myrtles with water to wash off existing spores and prevent germination of those landing on the wet foliage. For an active infection, mix a spray of one part skim milk in nine parts water. This formula controlled powdery mildew on grapevines without affecting the fruits, according to researchers at Australia's University of Adelaide. Weekly spraying of Brazilian squashes and melons reduced their symptoms by up to 90 percent, reports the National Gardening Association.
3. White Wood Rot Fungus
Crepe myrtles' second white fungus brings serious trouble. White rot results when turkey tail fungus (Tagetes versicolor) spores enter the plants through bark damage or wounds. Over a period of months or years, the fungus decays them from the inside. Affected plants develop white, spongy wood. Rainbow-patterned fruiting bodies in shades of brown, green, purple or orange confirm the disease. From spring to fall, these fan-shaped growths sprout from wounded bark and dead or dying wood. Crepe myrtles with advanced turkey tail infection eventually collapse.
4. Managing Turkey Tail
No fungicide treats internal turkey tail damage. Your best hope is to slow its spread by maintaining your crepe myrtles' vigor. Feed them in spring with 1/2-pound of 12-4-8 granular fertilizer scattered evenly over every 100 square feet of root zone and watered into the soil. Water blooming plants regularly during prolonged dry periods. Prune the affected branches back to their collars, where they intersect with larger branches or the trunk. If turkey tail invades their trunks, your crepe myrtles are beyond saving.
- Southern Living: Crepe Myrtle -- Essential Southern Plant
- The United States National Arboretum: Crape Myrtle Questions and Answers
- University of California Statewide Integrated Pest Management Program: Powdery Mildew on Ornamentals
- Science Daily: Drop Of the White Stuff The Right Stuff For Vines
- National Gardening Association: Got Mildew? Get Milk!
- University of California Statewide Integrated Pest Management Program: Wood Decay Fungi in Landscape Trees
- Fairfax County Public Schools: Study of Northern Virginia Ecology: Turkey Tail
- University of Georgia College of Agriculture & Environmental Sciences: Crape Myrtle Culture