The plants in my backyard are covered with all this black, sticky stuff. I think it is coming from one of my shade trees. What is it, and what can I do about it? -- Tammy

A: This is the No. 1 question I have gotten the last two weeks.

The problem is, we have a large infestation of Asian woolly hackberry aphids, small white insects that come off hackberry trees (also referred to as sugarberry) and just seem to float in the air.

This also occurred in 2001, when there were so many of them it looked like it was snowing every day, and in 2006.

The aphids are frequently mistaken for whiteflies, which also can be common on gardenias and anything in the privet family. But the aphids come only from hackberry trees. If you find them on other plants, it is just because they have landed there.

Hackberries have light-gray bark with narrow, corky, projecting ridges that are sometimes reduced to wartlike projections.

These aphids cause the same problems whiteflies and other aphids do: They suck the juice out of the leaves and secrete sticky honeydew on them. The parasitic fungus -- sooty mold -- then grows as a result. So you have a black, sticky mess, not only on the hackberry tree but also on any plant or item below it, including your car or patio furniture.

The insects have several generations per year, so they can become very abundant by late summer.

Ladybird beetles are beneficial insects that eat these aphids.

You have three choices for control of these woolly hackberry aphids:

- Cut the tree down. Of course, if you do that, you won't have to worry about the problem again, but you also may lose valuable shade.

- Hire an arborist to spray the tree. You are looking at an instant kill, but it is impractical for people who have large trees and live in subdivisions.

- Use the insecticide imidacloprid, which is sold as Bayer Advanced Tree and Shrub Insect Control. This is applied as a drench on the ground around the tree. The material takes several weeks to make its way up the tree, so the downside of this is it's too late to be effective this year.

Make the application in the spring, shortly after the leaves come out on the tree. Killing the first generation of these aphids can go a long way in preventing a buildup during the rest of the summer.

It is supposed to last one year but for certain trees, particularly large ones, you might put out the first application in the spring and follow it up with an application in late summer.

Don't overlook hackberry bushes, as they can come up everywhere near the hackberry tree. Cut them down or spray with the Systemic Insect Spray.

The aphids will not kill your tree but they are a big nuisance because of the mess that is deposited all over whatever is underneath the tree. I suppose all the car wash owners appreciate the mess.

REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.