(News article for April 2018)
Crape myrtles are one of the most iconic trees for southern Louisiana landscapes.Their vibrant flowers, long blooming season, disease and pest resistance, and relatively small size make them an excellent tree to add to your yard.
Before you buy a crape myrtle tree you need to have a plan. How big of an area do you have? Are you planting near a house or deck? What color do you like? These factors will determine what cultivar is best for your landscape.There are over 100 cultivars of crape myrtle trees but only 10-15 are readily available at garden centers around south Louisiana. When choosing a cultivar the most important thing to think about is the amount of space available for the tree. Crape myrtles are classified by size. Miniature trees reach heights of 2 to 3 feet; dwarfs 5 to 6 feet; semi-dwarf 10 to 12 feet; medium 15 feet; and tall 20 feet or higher. Crape myrtles need to be planted 8-10 feet away from a house so they will have plenty room to grow.
Dwarf/semi-dwarf cultivars to consider are Hope (white, 4-5 feet), Hopi (medium pink, 6-8 feet) and Tonto (red, 10-12 feet). Taller cultivars to consider are Acoma (white, 12-15 feet), Sioux (hot pink, 15 feet), Osage (light pink, 15 feet), Yuma (lavender, 15 feet) and Catawba (violet purple, 12-15 feet). Other recommended cultivars can be found in the LSU AgCenter publication “Crape Myrtles for Louisiana Landscapes.”
When planting trees, be sure to choose a sunny location with well-drained soil. Crape myrtles do well with pine straw mulch. Mulch will help retain moisture, prevent weeds and prevent damage from lawn equipment. The trees will benefit from a yearly fertilizer application of 8-8-8 or 13-13-13. Apply in early spring by broadcasting over the top of the soil.
Crape myrtle pruning is a hot topic of debate. The best way to prune your crape myrtle is by selective pruning to thin out the canopy. Prune in January or February when the plant is dormant. For tree-form specimens, remove all suckers growing from the base of the plant each winter. Remove any branches that rub against each other as well as any weak or crowded limbs. Dead limbs may be removed anytime. “Topping” the tree, or removing all the branches down to the trunk, is a popular way to prune crape myrtles; however, it is not healthy for the tree. It causes scarring and can leave the tree susceptible to disease.
Crape myrtles are relatively disease- and pest-free, but there are a few things you need to watch out for. Powdery mildew is a fungus that reduces flowering and weakens the plant. Look for a grayish-white powdery growth on the leaves and treat with a fungicide if the tree is infected. Cercospora leaf spot causes severe defoliation. It is prevalent during wet periods and causes black spots on the foliage. Cercospora leaf spot can be prevented or treated with regular applications of fungicide.
Aphids are the primary insect pest that affects crape myrtles. Watch for the insects or the honeydew they excrete. The honeydew will grow a black sooty mold on the leaves and stems. That is how you will know you have an insect problem. Apply imidacloprid around the base of the tree once each spring to prevent aphids.
Recently, scientists discovered a new insect affecting crape myrtles called the crape myrtle bark scale. When a tree suffers from the scale, branches and stems will be covered with felt-like scales, and sooty mold grows on the honeydew excretions from the scale. Scientists are still working on an effective treatment plan for bark scale, but horticultural oils and insecticides applied as a basal soil drench have shown control effects in field trials. Contact my office if you have trouble with bark scale.
Jessie Hoover is a County Agent with the LSU AgCenter covering horticulture in East Feliciana, West Feliciana, St. Helena, and Tangipahoa parishes.For more information on these or related topics contact Jessie at 225-683-3101 or visit The LSU AgCenter Website.
Crape myrtle flower- Photo by Keith Weller, USDA Agricultural Research Service, Bugwood.org