Why Are My Bay Leaves Curling?

Bay sucker

Bay sucker (Trioza alacris) is the most common and most distinctive pest of bay laurel in the UK and across Europe. The adult is a tiny winged psyllid (jumping plant louse) that lays eggs on developing bay leaves in spring and early summer. The nymphs that hatch feed by piercing the leaf margin and extracting sap, injecting a growth-regulating substance that causes the leaf edge to roll downward and the adjacent leaf tissue to thicken dramatically into a pale, cushion-like swelling. The nymphs are pale green, flat, and covered in waxy white filaments; they live concealed inside these rolled, thickened leaf margins. The damage is one of the most recognisable symptoms in the UK herb garden: instead of flat, smooth leaves, affected bay leaves have their margins rolled over and swollen in a way that resembles a rolled cigar edge. The upper leaf surface above the rolled area often yellows. Bay sucker rarely kills bay plants but the damage is disfiguring on topiary or decorative specimens, and large infestations weaken the plant over time.

What to do

• Pick off and destroy affected leaves promptly from May onward: removing the rolled leaf margins removes the nymphs living within them and interrupts the pest life cycle. This is the most effective control on lightly or moderately infested plants.
• Cut back heavily affected growth to reduce the overall nymph population and stimulate the plant to produce fresh, clean leaves. Bay tolerates hard pruning well.
• On severely infested plants where physical removal is impractical, a systemic insecticide labelled for bay can be applied in spring before new leaves unfurl. Note that bay treated with systemic insecticide should not be used for cooking until the re-entry interval on the label has passed.
• Natural predators, particularly blue tits and other small birds that actively search for insects on woody plants, provide useful control of bay sucker nymphs. Encouraging birds into the garden by providing food and nesting sites helps long-term.

Scale insects

Soft scale (Coccus hesperidum and related species) commonly infests bay laurel, particularly on plants grown indoors or in sheltered positions. Scale insects are small, brown, oval, limpet-like insects that attach themselves to stems and the undersides of leaves, sucking sap. A heavy infestation causes the leaves to yellow and droop, and the scale insects excrete large quantities of honeydew (a sticky, sugary liquid) that coats the leaves and stems and promotes the growth of black sooty mould, which further weakens the plant by blocking light. Scale insects on bay are most common on plants brought indoors for winter and in sheltered outdoor positions in the south and east of England.

What to do

• Inspect bay stems and the underside of leaves regularly, particularly on plants that have been indoors. Soft scale can be removed physically using a soft brush or cloth dipped in a dilute solution of washing-up liquid and water, scrubbing the stems and leaf undersides thoroughly.
• Insecticidal soap or plant oil spray provides contact control of soft scale, though complete coverage of all stem surfaces and leaf undersides is essential.
• The parasitic wasp Metaphycus helvolus is available as a biological control for soft scale on bay trees grown under cover.
• Wipe sooty mould off leaves with a damp cloth once the scale infestation is under control: the mould disappears naturally once the honeydew source is removed.

Cold damage

Bay laurel is borderline hardy in the UK and suffers in hard winters, particularly in exposed positions and in pots. Cold damage causes the leaves to curl, yellow, and drop; stem tips and younger growth may be killed outright. After a hard winter, a bay tree may lose most of its leaves and appear dead, but established trees and those in sheltered positions often re-shoot from living wood lower on the stems when warmer weather arrives in spring.

What to do

• Move potted bay trees under cover (frost-free greenhouse, cold frame, or porch) before the first frosts, or wrap the pot in bubble wrap and the foliage in two or three layers of horticultural fleece during periods of hard frost.
• Plant garden bay in a sheltered position, ideally against a south or west-facing wall which provides significant cold protection through radiated heat.
• In spring, do not cut out potentially dead wood until growth resumes: scratch the bark of apparently dead stems with a fingernail to check for green tissue beneath. Wait until May before concluding that wood is dead. Cut back to live wood and apply a balanced fertiliser to encourage regrowth.

Drought

Drought causes bay leaves to curl inward, turn yellow-brown at the tips, and eventually drop. Established, in-ground bay trees are quite drought-tolerant but young trees and those in pots are much more susceptible. Bay in terracotta pots is particularly prone to rapid drying in hot summer weather, as terracotta is porous and loses moisture quickly.

What to do

• Water bay trees in pots regularly during dry spells, checking the compost every 2 to 3 days. Large bay standards in terracotta pots may need daily watering in hot summer weather.
• Apply a thick mulch around the base of in-ground bay trees to retain soil moisture. Water newly planted bay trees regularly through their first two summers while the root system establishes.

Frequently asked questions

Why are my bay leaves curling at the edges?

Bay leaves curl most commonly because of bay sucker (Trioza alacris), a psyllid insect that is by far the most distinctive and recognisable pest of bay laurel in the UK. Bay sucker causes the margins of the leaves to roll downward and thicken, forming a conspicuous, pale yellowish or greenish cushion-like thickening along the leaf edge. The nymph stages of the pest live inside these rolled leaf margins and are concealed within the curled tissue. Other causes of curling bay leaves include soft scale insects, which weaken the plant and cause general leaf yellowing and distortion; cold damage, which causes the leaves to curl, yellow, and drop after hard frosts; and drought, which causes the leaves to curl inward and turn yellow-brown at the tips.

What is bay sucker and how do I control it?

Bay sucker (Trioza alacris) is a tiny psyllid insect (a jumping plant louse) that is the most common and distinctive pest of bay laurel in the UK. The adult is a small winged insect that lays its eggs on developing bay leaves in spring and early summer. The nymphs (immature stages) feed by piercing the leaf margin and sucking sap, causing the leaf edge to roll downward and the tissue to thicken into a characteristic pale, distorted cushion. The nymphs are pale green, flat, and covered in waxy white powder; they live inside the rolled leaf margins. Control options include: picking off and destroying affected leaves, which removes the nymphs inside; cutting back affected growth on a lightly infested plant; applying a systemic insecticide labelled for use on ornamental bay if the infestation is severe (note that treated bay should not be used for cooking until the re-entry interval specified on the label has passed); and tolerating light infestations on a large, established bay tree, as the damage is largely cosmetic.

Can I still eat bay leaves from a bay sucker-infested tree?

Yes, you can still harvest and use bay leaves from a bay sucker-infested tree, provided no systemic insecticides have been applied. Bay sucker does not make the leaves toxic or unsafe to eat; it causes cosmetic damage to the leaf margins by rolling and thickening them. Harvest leaves from unaffected parts of the tree and discard any that have visibly rolled or thickened margins. If you have applied a systemic insecticide to control the infestation, do not use leaves for cooking until the harvest re-entry interval specified on the product label has passed.

How do I protect bay from cold damage in the UK?

Bay laurel (Laurus nobilis) is borderline hardy in the UK: it tolerates mild winters with occasional light frosts but is damaged by hard, prolonged freezes (below about -5 to -10°C). In hard winters, the leaves curl, yellow, and drop, and young growth and stem tips can be killed. Established, in-ground bay trees often survive hard winters and re-shoot from the base or from living wood lower on the stem in spring. Bay in pots is more vulnerable because the roots freeze more easily. To protect bay: if growing in a pot, move it into a frost-free greenhouse, cold frame, or porch for the winter, or wrap the pot in several layers of bubble wrap or hessian to insulate the root ball; if growing in the ground in a cold area, wrap the whole tree loosely in horticultural fleece during periods of hard frost; plant bay in a sheltered position against a south or west-facing wall, which provides significant cold protection; in spring, cut out any frost-killed stems to live wood and apply a balanced fertiliser to encourage new growth.