Insects That Are Harmful to Lavender

Four-Lined Plant Bug

• The four-lined plant bug resembles a ladybug, except with yellow stripes instead of spots. It also has long antennae. One-quarter-inch long, these bugs are difficult to see because they hide under the foliage or drop to the ground when the plant is disturbed. They feed on the foliage, causing small brown spots that may become translucent or drop out, leaving a shot-hole effect on the leaf. Treat light infestations with insecticidal soap or summer-weight horticultural oil. Heavy infestations require the use of an insecticide. If you cook with your lavender or make soap or oils with it, ensure that all insecticides are safe for use on food crops.

Whiteflies

• Minute sucking insects, whiteflies are primarily a problem on lavender grown indoors or in greenhouses. Infested plants lose vigor and are more susceptible to disease and other insects. Whiteflies congregate on the underside of the leaves. If found, take a sample to your garden center or local cooperative service for identification, since proper control varies with the species of whitefly.

Boxelder Bugs

• If you've ever come across a mass of black bugs with red chevrons on their backs sunning themselves on a warm, south-facing wall in the fall, you're familiar with boxelder bugs. These bugs are a nuisance rather than being really harmful. Their host plant of choice is the boxelder maple, but they feed on other plants, including lavender, if necessary. Keeping your yard clear of debris where boxelder bugs can overwinter is the best prevention. Most infestations can be washed off your plants with a strong stream of water. Insecticides are effective but must be reapplied regularly.

Nematodes

• Lavender is susceptible to the northern root nematode, a microscopic, soil-borne worm that feeds on plant roots. Galls or knots form on the roots, and affected plants weaken and wilt quickly, because root function is impaired. There are no chemicals suitable for home use to control nematodes. Keep your lavender plants as healthy as possible to discourage infestation, since nematodes favor drought- or disease-stressed plants.