Aphids suck plant juices but can be controlled with Diazinon dust or sprays of Sevin, Orthnene, or rotenone.
Beetles of several types eat the leaves. Flea beetle chews small shotholes in the leaves. Control this insect with applications of rotenone, Sevin, of methoxychlor.
Mites cause yellowed foliage. The insects are so small they are usually not noticed. Spray with rotenone.
Slugs eat the leaves at night and leave slime trails on the leaves. Use baits containing Mesurol or metaldehyde.