Friday, June 1, 2012

Crape Myrtle Magic

Who can deny the completeness of beauty found in the Crape Myrtle tree?  the glorious outbreak of Spring-time leaf, the fragrant splendor and abundant, unrestrained Summer bloom, vibrant Autumn hues of gold-red-and orange, and the quiet picturesque Winter structure of the muscular, buff colored trunks.  Undeniably, the Lagerstroemia indica `Crape Myrtle’ is the most popular, vastly planted small flowering tree in the Southeastern United States.

Select the right Crape Myrtle for the space requirement so only minor pruning is needed.  Ideally prune in late winter, when the tree has no leaves and the branches are easily seen.  Remove small twiggy branches inside the plant to promote good air circulation.  Remove crossing, rubbing and dead branches. Remove lower branches or suckers that grow from the base of the trunk.  Crape Myrtles bloom on the current season’s growth, so they can be pruned in the Spring without loss of flower buds.  Clipping faded blooms at their base will encourage another round of blossoms.

Fertilize in late winter to early spring with a complete general-purpose garden fertilizer, such as 8-8-8, or 10-10-10 at a rate of 1 lb. per 100 sq.ft., or 13-13-13, or 12-4-8 at a rate of ½ lb. per 100 sq.ft.  Preferably, drill holes in the ground about 8 inches deep near the drip line (encourages lateral roots for better anchorage), and use a granular fertilize with a systemic insecticide for pest control. 

Planting Crape Myrtles in full sun with good air circulation and proper drainage greatly diminishes pest problems.  Also consider planting improved disease resistant Crape Myrtle varieties.   Disease and insect problems are less severe in open, sunny sites.

Powdery mildew is a fungus disease developing in late Spring and Fall and is associated with warm days and cool nights and high humidity.  Leaves, young shoots and flowers are heavily coated with a powdery, white mold that can distort new growth.  Infected flower buds may not open, and severely infected leaves and buds often drop early.

Cercospora leaf spot is another damaging disease for Crape Myrtles.  Spots develop in mid-summer through Fall during wet, humid weather.  Large, dark brown spots develop on lower leaves and progress upward through the plant.  Infected leaves turn yellow around the spots and drop prematurely. 

Powdery mildew and leaf spot can be controlled by applying fungicides when the diseases are first noticed.  The best approach to prevent diseases is to plant disease resistant Crape Myrtle cultivars, such as Basham’s Party Pink, Hopi, Lipan, Sarah’s Favorite, Tuscarora & Catawba.

Crape Myrtle aphids are small pale yellowish green in color, and found on the underside of the leaf.  Several generations are produced each growing season, with the aphids sucking plant sap from tender new leaves.  The aphid then excretes large amounts of sugary sticky liquid called honeydew.  The honeydew serves as food for the sooty mold fungi.  The aphid also injects saliva into the leaf, causing yellow spots and distortion to the leaves. 

Ladybird beetles (lady bugs)and other beneficial insects feed on the Crape Myrtle aphid.  As much as possible, these natural predators should be allowed to reduce aphid populations.  In addition, aphids can sometimes be removed by spraying plants with strong streams of water. 
Insecticidal soaps, neem oil, or soil drench systemic insecticide may be necessary for control. 
Best alternative is to plant Crape Myrtle hybrids that have a moderate resistance to aphids, such as Natchez, Muskogee, Tuscarora, Acoma, Tuskegee, Hopi, Lipan, Sioux and Comanche.

Sooty Mold indicates that there is an insect problem on the plant.  A black sooty substance covers the leaf and stem surfaces, causing them to appear black and dirty.  These molds are caused by fungi that grow on the sugary substance, called honeydew, produced by the excretions of Aphids, scales, mealybugs or whiteflies.  Sooty Mold can be washed from the leaves by drenching with a dish soap solution (4 ounces per gallon of water), waiting three to four minutes, and then blasting the foliage with a strong stream of water.  If you control the insect, no sooty mod will develop.

Lichens are an unusual organism composed of a fungus and an alga living together in the same body.  Lichens often appear as green to gray-green crusty growths on the trunks or branches of plants.  Typically, they occur on plants that are declining in health or vigor.  They are harmless to the plant and in no way responsible to the poor health of the plant.  Lichens will gradually disappear if the health of the plant is restored.  However, an application of copper sulphate can be used in January-February to reduce an unattractive appearance.