Crepe myrtle emergency!

C. D. Scallan
by C. D. Scallan
White flies are leaving black soot looking residue all over the trees and they're killing the crepe myrtles. We have tried neem oil, Dawn, alcohol and combinations of the above but nothing is helping . Is there anything else we can try? My husband is so frustrated he wants to pull them up and start over!

  5 answers
  • Wow! Sounds like you have tried everything I would have suggested. Might consider calling in a local arborist. Pulling them up and starting over may not be the ticket - just yet, could be something in the soil too attracting the white flies. Might be easier to fix the ones you already have?

  • Molly Anmar Molly Anmar on Jul 17, 2017
    Sooty mold indicates that there is an insect problem on the plant. These common molds are caused by fungi that grow on the sugary substance, called honeydew, produced by various insects that suck sap from the plant. Aphids, scales, mealybugs and whiteflies most commonly cause this problem.

    Sooty molds are unsightly, but are relatively harmless, since they do not directly attack the plant. Controlling the insect problem can reduce excessive amounts of sooty mold. Reduce aphid numbers by allowing beneficial insects such as lady beetles to inhabit the plant. Aphids can sometimes be washed from the plant with a strong stream of water.

    Although not necessary, 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 washing the foliage with a strong stream of water

    Whiteflies have many natural enemies in the garden setting, such as spiders, lady beetles and lacewings. However, frequent or widespread use of insecticides to control other garden pests prevents these predators from effectively controlling whitefly populations

    The use of traps can be very helpful in controlling light infestations of whiteflies in greenhouses. You can make a trap from a 12-by-6-inch strip of cardboard or strong poster board. Paint both sides bright yellow and coat with a sticky substance, such as Tanglefoot, petroleum jelly, petroleum jelly/mineral oil mix, mineral oil or a heavy-grade motor oil (SAE 90). Hang the trap vertically or support it on stakes just above the plants. The adults are attracted to the yellow color and become trapped on the sticky substance. Whitefly traps are available commercially also.

    In many cases, controlling whiteflies with insecticides has been difficult because they have developed resistance to some chemicals. Because of this resistance, a certain product may work well in one area but not in another. Resistance may be delayed by alternating the types of chemicals used. In addition, the eggs and nonfeeding pupae are generally not as susceptible to insecticides as are the nymphs and adults. Consequently, eradication of a whitefly population usually requires four to five applications of a registered insecticide at five- to seven-day intervals. Be sure the applications are made to the lower leaf surface. Apply the insecticide as soon as whiteflies are detected; do not wait until populations become severe.

    Over-the-counter insecticides commonly used for whitefly control include neem oil, insecticidal soap, horticultural oil, pyrethrins, permethrin, imidacloprid and malathion.

    Before you use any insecticide for whitefly control, make sure that both the site and the target plant are listed on the label. Follow label directions carefully.
    See if you don't find this informative:

  • Ell7769207 Ell7769207 on Jul 17, 2017
    I have the same issue. I also had white soot as well as black soot which may be a fungus. I sprayed them twice wih Bayer tree and Shrub insect control, giving the shrubs a glossy covering.
    You have to get under the leaves real good. Also I cut 2 inches below the damage leaves and stems. From what I read, it is most important to cut off all damaged leaves and branches. Otherwise it will return.
    Everyday I check them and cut off what additional dead leaves and branches that I may have missed. It's been 5 days now and it seems to be working for me. I also bought a fungal spray to follow up in a day or to when the rain stops.
    I am fairly new to crepe myrtles and relied on Farmer's Almanac and the internet for answers. If it is does not work, take a the damaged leaves to a nursery center to help ID it. I hope I was helpful. Good luck.

  • C. D. Scallan C. D. Scallan on Jul 18, 2017
    Thank you everyone !