Laurus Leaves Curling
Bay sucker and scale insects are the most common reasons laurus leaves curl. This guide shows you how to identify each cause and keep your bay laurel healthy and fragrant.
1. Bay sucker (Trioza alacris)
Bay sucker is a tiny psyllid insect that spends its entire life cycle on Laurus nobilis. It is the single most common cause of curled, distorted leaves on bay laurel in UK gardens. The pest overwinters as an adult on the plant, then lays eggs on the young leaves emerging in spring.
What to look for
Leaf margins curl downward and inward, thickening noticeably as they do so. The curl often turns yellow or light brown at the edge. Part the curled margin and you will see the flat, waxy, cream-coloured nymphs feeding on the underside. White waxy threads or globules may also be present. Severely affected leaves may drop early. The damage is most obvious on young flush growth in spring and early summer.
What to do
Remove and bin all affected leaves as soon as you see them to reduce the population before the adults emerge later in the season. Do not compost affected material as adults can overwinter and re-infest. If the infestation is severe, spray the undersides of leaves with a plant-based fatty acid spray or a horticultural soap solution in spring when nymphs are first visible. Repeat every ten days for a month. Avoid broad-spectrum insecticides which also kill the natural predators, including several parasitic wasps, that help to keep bay sucker populations in check long term.
2. Scale insects
Bay laurel is susceptible to several species of scale insect, most commonly soft scale (Coccus hesperidum) and bay laurel scale. These sap-feeding insects attach to stems and the undersides of leaves, secreting honeydew that encourages the growth of black sooty mould.
What to look for
Look for small, flat, oval or dome-shaped brown or yellowish bumps on stems and the undersides of leaves. Infested leaves curl slightly, turn yellow, and may drop prematurely. A sticky film on leaves and surfaces below the plant is a sure sign of honeydew production. Black sooty mould then colonises this sticky deposit, turning leaves and stems dark grey or black. The mould itself does not infect the plant but it blocks light and reduces vigour.
What to do
Scrub accessible scale off stems and leaves using a soft toothbrush dipped in soapy water, or spray thoroughly with a plant oil-based insecticide or horticultural soap solution. Time treatment for late spring when the mobile first-instar nymphs (crawlers) are active; the waxy shell that covers older scale makes them much harder to kill. Wipe sooty mould off leaves with a damp cloth once the scale is under control. In late summer, the parasitic wasp Metaphycus helvolus provides natural control and should be given time to work before repeat spraying.
3. Drought stress
Bay laurel is frequently grown as a topiary standard or clipped ball in containers, where it is especially prone to drought. The combination of a restricted root volume, dense clipped canopy, and warm summer temperatures means container-grown bay trees can dry out within a day or two during hot weather.
What to look for
Leaves roll inward along the midrib, reducing their surface area. The foliage takes on a slightly duller, greyer tone than usual. Lower leaves may yellow and drop. In severe drought, leaf tips and margins brown and crisp. The compost in the container will feel bone dry when you push a finger into it. On established plants in the ground, drought tends to cause wilting rather than curling.
What to do
Water container-grown bay thoroughly until water drains freely from the bottom of the pot. During warm summer weather this may be needed every day for a large pot in a sunny position. If the compost has dried out and is repelling water, stand the pot in a tray of water for 30 to 60 minutes to allow it to rehydrate fully from below. Mulching the compost surface with a layer of gravel helps reduce evaporation. Use a slow-release fertiliser each spring to sustain healthy growth through the season.
4. Cold damage
Laurus nobilis is broadly hardy in the UK but can be damaged by severe frosts, icy east winds in late winter, or a sharp spring frost that catches emerging new growth. Container-grown plants are more exposed than those in the ground and suffer more frequently.
What to look for
Leaves curl downward and their margins turn brown or black, particularly at the tips. The damage often appears suddenly after a hard frost and is worst on the outermost and uppermost foliage. Young unfurling leaves are the most vulnerable. In severe cold the leaves may dry out completely and hang limp on the branch before dropping.
What to do
Do not remove cold-damaged leaves immediately; they can still protect the buds beneath them. Wait until late March or April when the risk of further frost has passed, then cut back to healthy green wood. New growth will emerge from dormant buds below. Move container plants to a sheltered position against a south-facing wall or into a frost-free greenhouse or garage during the coldest months. Wrap the pot itself in bubble wrap or hessian to protect the roots, which are more frost-sensitive than the top growth.
5. Bay stem canker (Neofusicoccum parvum)
Bay stem canker is a fungal disease that typically enters through wounds, pruning cuts, or frost-damaged tissue. It causes dieback of individual branches, and the associated wilting and leaf curl can be mistaken for a pest problem or simple drought if the underlying stem lesion is not noticed.
What to look for
Leaves on one or more branches wilt, curl, and turn brown without any obvious pest or drought explanation. The affected branch may show a dark, sunken canker on the bark just below the point where the wilting begins. If you cut the stem at the canker, the wood beneath is dark and discoloured rather than the healthy cream-white of sound wood. Multiple branches can be affected on badly infected plants.
What to do
Cut out all cankered material immediately, pruning at least 15 cm below any visible discoloration. Sterilise your pruning tools with a 10 percent bleach solution or methylated spirits between cuts to avoid spreading the fungus. Dispose of removed material in the bin, not the compost heap. There is no chemical cure; the key is to catch the disease early and prune well behind it. Reduce susceptibility by making clean, angled pruning cuts that shed water quickly, and avoid pruning in wet weather when fungal spores are most likely to colonise fresh wounds.
Frequently asked questions
What causes the edges of bay leaves to curl and thicken?
Thickened, curled leaf margins are almost always caused by bay sucker (Trioza alacris). The nymphs feed on the underside of leaf margins, triggering the leaf tissue to become swollen and curl over them. Part the curled edge and look for the pale, waxy nymphs to confirm the diagnosis.
Is bay sucker harmful to laurus?
Bay sucker is more of a cosmetic nuisance than a serious threat. Heavy infestations can distort young growth and reduce vigour, but rarely kill established plants. Prompt action each spring to remove the first generation limits damage before populations build.
Can I still use leaves from a laurus with bay sucker?
Yes, unaffected leaves are perfectly safe to use in cooking. Simply pick leaves that show no curling or thickening. Avoid using the distorted leaves as they may taste slightly bitter. Wash all leaves before use as a precaution.
How do I treat scale insects on bay laurel?
Scrub visible scale off with a soft brush dipped in soapy water, or spray with a plant-based oil such as neem or a horticultural soap solution in late spring when the crawlers (mobile young) are active. Repeat at two-week intervals for six weeks. Avoid broad-spectrum insecticides that kill the natural predators that keep scale in check.
Why are my bay tree leaves curling in summer?
Summer leaf curl on bay is usually caused by drought stress, particularly in container-grown specimens. Bay trees in pots need watering regularly during warm weather, often every day in a heatwave. If the compost has dried out completely, stand the pot in a tray of water for an hour to allow it to rehydrate fully.
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