A. Healthy rhododendrons are tolerant of the kind of severe pruning you are contemplating. Although you normally prune them when they finish blooming, severe pruning is best done in late March. You will sacrifice next year's flowers. Rhododendrons bloom on old wood, which means that they set flower buds for next year as soon as they finish blooming this year. If you prune after the buds are formed, you remove the following season's flowers. The type of severe pruning you want to do is stressful to the plant, and is best done before they bloom. That way, the rhododendrons can put their energy to regrowth and recovery rather than flowering.

Be sure to use hand pruners and limb loppers rather than hedge shears to maintain the lovely natural shape of the plants. You will notice that rhododendrons grow in whirls of foliage separated by a length of stem. If you prune back to a lower whirl of leaves or a side branch growing off of a main stem, you maintain the attractive natural growth habit of the plant while substantially reducing the size.

There are buds at the base of the leaves that will grow into new stems. It is always best to leave outward-facing branches and buds while removing those that grow back into the plant. Directing the growth out permits good light penetration and air circulation in the middle of the plant, which is important to the overall health of your rhododendrons.

Q. My Nicotiana is being devoured by something; there is little left of the leaves besides the mid-vein. When I looked under what is left of the leaves, I saw these small slimy yellowish insects that seem to be the source of the damage. Can you tell me what they are and what I can do to get rid of them?

A. The writer enclosed a sample of the insect in question. We have had the same insects eating the foliage of angel's trumpet (Datura metel 'Cornucopia') in our demonstration garden at North Park. They are the larvae of three-lined potato beetles (Lema trilinea). The grayish-yellow larvae feed as a group, lined up side by side. They move backward from the edge of the leaf toward the center as they feed. They are "slimy" because they are coated with their own excrement, a disgusting but very effective survival technique. They usually feed on plants in the nightshade or Solanaceae family, which includes Datura, Nicotiana, tomatoes, eggplant, potatoes, peppers and those species considered weeds, such as bittersweet nightshade (Solanum dulcamara). These plants are high in alkaloids that make them toxic to animals, including people.

One of Penn State's doctoral candidates, Tim Morton, is doing research on these insects. He has found that the alkaloid content of their excrement is key to their survival. When he removed the excrement from the larvae or fed them an innocuous diet of lettuce, predators made short work of them. Those consuming their preferred diet of nightshade were unharmed.

The adult beetles are reddish-yellow with three black stripes running lengthwise down their wing covers. They become active when tomato and potato plants (or other preferred crops) are planted out in late spring or early summer. They lay clusters of small yellow eggs on the underside of leaves. When the larvae hatch, they begin feeding on the foliage. They are able to coat themselves with excrement because their anus is in the middle of their backs. They feed for about two weeks and then drop to the ground to pupate.

Control options include removing severely infested leaves and crushing the insects or sealing them tightly in a plastic bag and sending them out with the trash. You can also make insecticide applications to control them. Rotenone, pyrethrins and Sevin (carbaryl) are labeled to control three-lined potato beetle.