Bay Tree Pests and Diseases

Long before bay laurel trees (Lauras nobilis) made their way to the U.S., their leathery, dark green leaves crowned Grecian nobles. Those same fragrant, flavorful leaves provide the crowning touch to many culinary delights. Hardy in U.S. Department of Agriculture plant hardiness zones 8 through 10, these Mediterranean natives grow up to 40 feet tall. Healthy bay laurels repel most pests and diseases, but a few unwelcome guests occasionally affect these trees.

Oleander scale, an armored scale insect, attacks bay laurels with piercing-sucking mouth parts. Unlike soft scales, oleander scales don't secrete honeydew, and they bear platelike armor. The pests stay in one spot their entire lives and have several hatchings each year. Damaged laurel foliage may wilt, yellow and drop as plant growth slows. Beneficial parasitic wasps attack oleander scale. Horticultural oil applied in late winter through spring to vulnerable hatching nymphs also helps. Mix 5 to 7 tablespoons of horticultural oil concentrate with 1 gallon of water, and spray affected surfaces thoroughly. Wear gloves, protective clothing and safety goggles when you spray. If you plan to use the bay leaves for cooking, double-check that the horticultural oil you've chosen is safe for food plants.

Laurel psyllids, small sucking insects, are often referred to as "jumping plant lice." Most active in warm weather, they hatch up to five generations each year. While native psyllids decline naturally, these introduced, nonnative, invasive pests don't. They suck plant juices and excrete honeydew that leads to black sooty mold. Both adults and nymphs prefer succulent new growth to lay eggs and to feed. Laurel tips may distort, discolor and die back, but the damage is rarely fatal. Weak, stressed plants suffer most. Avoid nitrogen fertilizers, which encourage soft growth, and minimize shearing. Beneficial lady beetles, lacewings and parasitic wasps help. Horticultural oil, applied as for scale, is also effective.

Tiny sucking insects known as greenhouse thrips leave laurels with unsightly foliage. They suck plant juices, leaving stippling discoloration behind. Affected leaves take on a silvery appearance as laurel flowers and fruit distort. Greenhouse thrips may have eight hatchings per year. Though unattractive, the damage rarely threatens bay laurel survival. The pests tend to move slowly and not fly, but control remains difficult. Parasitic wasps feed on greenhouse thrips eggs, and beneficial lacewings and pirate bugs prey on larvae and adults. Avoid excess nitrogen and shearing, and keep plants healthy to prevent infestations. If needed, spray horticultural oil at scale rates, and cover laurel buds and tips thoroughly.

Bay laurel problems often arise from improper care. Healthy trees resist pests and disease. Overwatering and poor drainage are frequent culprits. Plant bay laurel where it gets full sun to light shade and well-draining soil. Water your laurel away from its trunk, focusing beneath the canopy. Water deeply and infrequently, and don't allow the soil to stay soggy. Soil-borne Phytophthora pathogens cause crown and root rot disease when bay laurels suffer prolonged periods in overly wet soil. Phytophthora begins at the roots, rises to the crown, kills the tree's inner bark, and ultimately kills the tree. Proper care and good drainage prevent these diseases.