Tree/shrub Tops Blacken, Die Back In Spring means Cold Weather
In some northern areas crape myrtles are victims of cold snaps which kill their tops. Their roots are generally cold hardy, however, so simply prune off the dead material early in the spring before growth starts. The plant will sprout new growth and bloom on schedule.
Crape myrtle Fails to Bloom indicates the plant was Pruned Too Late
Crape myrtles bloom on wood that is form in the current growing season. If pruning is delayed until the new shoots have begun to grow and they are cut off, flower buds will not form. The tree is basically all right and will bloom next season. Always prune before growth starts in the spring.
Foliage Curls, Turns Yellow shows Aphids
Check crape myrtle stems and leaves for bunches of soft-bodied, pear-shaped, insects a little bigger than the head of a pin. They may be white, yellow, red or brown. These are aphids, which suck sap from leaves and stems of crape myrtles, causing them to curl and turn yellow. As they feed they secrete a sticky "honeydew" on the foliage that coats it. It, in turn, encourages sooty mold fungus, which then coats the leaves in black.
To dislodge light aphid infestations, spray the undersides of foliage vigorously with water three times, once every other day, in the early morning. If aphids persist, spray them with insecticidal soap every 2 to 3 days, making sure to hit the insects with the spray. As a last resort, spray them directly with encapsulated pyrethrum. Take care to use pyrethrum late in the day to minimize killing honeybees and other beneficial insects that reside in the yard. If serious aphid problems recur every year, spray dormant oil spray on the crape myrtle trunks and stems late in the winter before leaves begin to develop. This will smother overwintering aphid eggs.
For more information see file on Controlling Aphids.
Leaves Stunted; Coated With White Powder indicates Powdery Mildew
This fungal disease is a serious problem on crape myrtles from Maryland to Florida and out to Texas and in the North on trees planted near the seashore or other cool, foggy areas. It also sometimes strikes these plants which are in shady locations. It winters over in dormant buds and shows small white circles on new leaves when spring arrives. Then it spreads to new, young shoots and eventually to the larger leaves. Affected plant parts are coated with a dusty white growth and the leaves are stunted and thickened. Sometimes they are only 1/3 normal size. Stems are stunted, flower buds fail to develop. Diseased plant parts sometimes drop off in a week or two and the plant may recover and produce new growth when hot weather arrives. Where powdery mildew is common, spray trees with lime sulfur in early spring as the buds break. Repeat this spray 2 weeks later. If the infection persists, spray all affected plant parts with wettable sulfur or dust with sulfur. Plant in open, airy locations with plenty of sun. Mildew resistant varieties of crape myrtle are hybids `Biloxi', `Miami', and `Wichita'.
For more information see file on Controlling Fungal Disease.
Leaves Near Stem Tips Turn Brown shows Tip Blight
A tip blight caused by a fungus sometimes attacks crape myrtles. Leaves near the branch tips turn brown in late spring or early summer. Tiny black spore-bearing bodies appear on infected leaves. Spray plants with copper fungicide or lime sulfur fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering which keeps foliage moist and fosters the disease. Prune to increase air circulation around plants, taking care to sterilize pruning tools by dipping them in household bleach to avoid spreading the disease. Because the fungus spores collect on the mulch beneath the shrubs, removing the old mulch and replacing it with fresh material may help prevent an outbreak from recurring.
If this blight is a common problem every year, prune and destroy affected plant parts in the early spring. Spray a copper fungicide or lime sulfur in four applications: (1) after the dead leaves and dying branches have been removed and before growth starts in the spring; (2) when growth is half completed; (3) after spring growth has been completed; and (4) after fall growth stops. Take care to determine if the crape myrtle twigs are turning brown from frost damage rather than disease.
For more information see file on Controlling Fungal Disease.
]Dead Blotches on Leaves means Leaf Spot
Various leaf spot fungi cause yellow, brown or black dead blotches on crape myrtle leaves. These blotches frequently run together. Heavily infected leaves then turn yellow or brown and fall prematurely. Cool, moist weather encourages these diseases, especially when new leaves are developing. Shake out all fallen and diseased leaves from the center of the crape myrtle and destroy them. Remove all dead branches from shrub centers, especially in crape myrtle hedges to allow better aeration. Mulching helps prevent the disease from splashing up from the ground and infecting plants. Spray at weekly to 10-day intervals with sulfur or Bordeaux mixture or other copper fungicide, particularly if weather is damp. Spray between rains. Dig up and discard seriously infected shrubs with their root system and soil ball in a bag for the trash. Clean up all debris, infected leaves, etc. to avoid spreading the fungus.
For more information see file on Controlling Fungal Disease.
