Crape myrtles are among the most commonly planted trees in the Southeast. The two main pests are crape myrtle bark scale which has not been reported in NC yet but is in Virginia and Tennessee. The other is crape myrtle aphid.
Crape myrtle aphids overwinter as eggs and hatch in April. For the rest of the summer crape myrtle aphids give birth to many nymphs. Large populations produce enough honeydew to completely coat leaves and other objects below, giving infested plants a sticky or shiny appearance. This is a nuisance when it comes to keeping decks and cars clean but also leads to black sooty mold growing on the tree leaves and stems (and the deck, lawn chairs, toys below). Black sooty mold is noticeable from affair and really detracts from the beautiful bark and form of the trees.
So, why do aphids go berserk? Many aphids, scales, mealybugs, and similar pests outbreak when their natural enemies are disrupted by the environment (heat, drought, pollution) or by insecticides. In many cases contact insecticides are better at killing predators and parasitoids that are actively moving around a landscape than pests which may be hunkered down in nooks and crannies. Pests often reproduce faster too. So, if they get a window of time with no natural enemies they can really achieve large populations.
Over the past several years I have noticed large populations of aphids on trees in yards that get routine mosquito sprays. I visited a yard last night that has a lot of aphids for so early in the season. Their mosquito service had already started for the year. They had a lot of aphids and I couldn’t find any natural enemies which is unusual when you have so much prey available. I appreciate the need to reduce mosquito populations. In the summer Asian tiger mosquitos in my neighborhood make you a hostage inside. However, we may need to apply some IPM to the mosquito programs to integrate them with landscape pest management programs. If aphids are becoming abundant the scales are probably thriving also.