Dr. Grow: Most unwanted

If you have azaleas in your landscape, read this article and then go out and inspect them. They may be infested with the insect at the top on Cape Girardeau's Most Unwanted list, the lace bug.

During the last four weeks I have probably looked at 30 or more samples of azaleas and have taken a comparable number of phone calls about lace bug. Because of the number of calls and samples brought in, I thought it important to write about them in this column.

Lace bugs are members of the order Hemiptera. This means that they have a hind set of membranous wings and a front set of wings that are one-half bony and half membranous. Their mouth parts are like tiny hypodermic needles, used to suck juices out of plant leaves.

Lace bugs feed primarily on azaleas. I have also seen large infestations on rhododendrons, pyracantha and hawthorn.

The first symptom that is manifested is stippling on the upper surface of leaves. Stippling looks like small white circles surrounded by the normal green leaf tissue. As the infestation gets worse, the stippling gets more prevalent until the stipples coalesce and the upper surface of the leaf turns gray to white.

The second symptom that you look for is tar spots on the underside of the leaf. It looks as if someone was roofing a house with liquid tar and some droplets were splattered under each leaf. These tar spots are actually fecal material from the lace bug.

If you find both stippling and tar spots, then look for the presence of the insect itself. Quite often you will find the skin casings of immature nymphs. These casings have distinctive spurs that are attached to the perimeter of the abdomen. The nymphs and their casings are usually so small that they can only be identified under a dissecting microscope or a hand lens.

The mature lace bugs are only one-sixteenth of an inch long. Their membranous wings have a mottled clear and black appearance. They are usually quite fast, so it is hard to see them.

If you find lace bugs or the symptoms of the infestation, you should spray the azaleas with cygon or diazinon. An insecticidal soap may or may not work. No matter what you use, make sure that you get the material on top of the leaf and under the leaf. Make applications two to three times, about a week apart.

Because the lace bug has removed chlorophyll and other plant materials from the leaf, the infested plant is under stress. Make sure that you reduce other kinds of stress that may affect the plant. Fertilize the azaleas with a good azalea food.