There are many examples of introduced insects that create problems for gardeners. The azalea lacebug, Stephanitis pyrioides, is one such pest. This delicate-looking insect was introduced from Japan in the early 1900’s and has spread along the east coast and recently has been discovered in the west as well. It specifically attacks azaleas, especially the evergreen varieties and also mountain laurels. Whitish stippling of the leaves is one of the characteristic symptoms of this pest and signs include the presence of nymphs, shed nymph skeletons, and shiny black tar-like fecal spots on the undersides of the leaves. These fecal spots are one of the diagnostic features that differentiates this pest from mites which can also cause leaf stippling. Besides creating unattractive foliage, if there is a large enough infestation, these insects can weaken a shrub enough so that it dies.
The adult lacebug is a pretty cream-colored creature with a flattened rectangular body and netted, transparent wings that extend beyond the body. Its wings are marked with a dark X. The nymphs are smaller and darker with a spiny body. This species of lacebug overwinters as eggs that the female inserted into the lower midrib of leaves the previous growing season. These eggs hatch in late April and May, and the nymphs immediately begin to feed on the leaves. They undergo 5 instar stages over the course of about a month and then, as adults, begin the cycle again. Often there are 2 or 3 generations each year. Lacebug adults and nymphs are plant fluid suckers. They use their sharp stylet mouthpart to pierce the plant leaf and suck out tissue from the chlorophyll containing layers inside the leaf. This loss of pigmented tissue leaves the whitish stippling on the surface of the leaf.
One of the best ways to deter a lacebug infestation is to grow your azaleas in the proper environment! Azaleas grown in full sun are 2 times as likely to be attacked by lacebugs. Those that are drought-stressed are also at risk. These acid-loving plants prefer part shade in a soil with a pH between 4.5 and 5.5. Mulching will help retain soil moisture, and they should be watered during a drought. If it is necessary to fertilize them, use a fertilizer designed for acid-loving plants. Luckily there are natural predators, such as ladybugs, lacewings, pirate bugs and spiders, which can also help control lacebugs.
Control measures should be taken early in the season before much stippling has occurred and while the nymph stages are small. Spraying the undersides of the leaves with a strong jet of water may help with mild infestations. Insecticidal soap or 2% horticultural oil or neem products are effective so long as the undersides of the leaves are thoroughly covered. These less toxic products will only destroy the insects which are contacted by the spray, but they may conserve some of the beneficial predators which tend to move around. More than one application may be needed. Alternatively, some synthetic or systemic insecticides can be used. Be sure to read the label to see if lacebugs are one of the target organisms and follow instructions carefully. Finally, there are some varieties of azaleas which are less prone to lacebug attacks, so, if you’ve had a problem with this insect, you might want to research some of these.
There is also a native lacebug that attacks rhododendrons and mountain laurels and another introduced species that attacks andromedas (Pieris). The life cycles and control measures for these are basically the same as for the azalea lacebug. Inspect your plants regularly for these pests—early detection makes control much easier!
I have rose bushes that get laced by little green worms...the leaves are destroyed by them...what can I use on the roses...
That sounds to me like roseslug sawflies which are the larvae of a wasp-like insect. You can use insecticidal soap on them.