Laurels, members of the genera Prunus, Laurus (sweet bay) and Kalmia (mountain laurel), are large shrubs or small trees. The different species and cultivars offer a variety of growth rates and forms, but they are commonly used for hedges, screens or shade trees. Laurels may be affected by a number of problematic insects.
Laurels may be bothered by aphids, small insects that use piercing mouth parts to feed on stems and leaves. These pests, which tend to concentrate on new growth and the undersides of leaves, also produce a sticky, sweet substance known as honeydew that attracts unsightly sooty mould. A heavy infestation can cause leaf yellowing and distortion and premature leaf drop. Aphids are often controlled by natural predators but are sometimes protected by ants that feed on the honeydew. Repeated, strong blasts of water will knock aphids off of plants. Avoid excessive nitrogen fertiliser applications that stimulate flushes of new growth.
Both armoured and soft scale species may feed on laurel shrubs. These insects appear as small, immobile bumps of varied colours on bark or leaves, where they use a straw-like mouth part to feed on plant fluids. A high scale population can cause leaves to wilt, turn yellow and drop prematurely and stunt plant growth. Soft scales also excrete honeydew. Scales are typically controlled best by natural predators, so avoid the use of broad-spectrum insecticides. Prune off heavily infested portions of plants and provide the shrubs with proper care. If necessary, control protective ants or address scales with well-timed applications of horticultural oil while the insects are in their vulnerable crawler stage.
Stressed or weakened laurels are especially vulnerable to an infestation of shothole borers (Scolytus rugulosus). The presence of this borer is indicated by a buckshot pattern of holes in the bark of infested branches and trunks, a gumming or dieback of woody portions and dust generated by the boring. Address the borer by removing and destroying infested plant portions.
Laurels may be eaten by caterpillars such as cutworms. These pests are dull-coloured larvae that grow 1 to 2 inches. Cutworms are only pests in the spring when they feed on leaves, blossoms and young shoots. This pest does not respond well to pesticides. The best control is to prune and destroy infested plant portions and provide the laurel with good care.
Additional Possible Pests
Laurels may occasionally be bothered by thrips, tiny, delicate-looking insects. Mountain laurel (Kalmia latifolia) is susceptible, in addition to borers and scales, to lacebugs and whiteflies. Circular holes in laurel leaves are probably caused by a fungal or bacterial disease rather than insects.