Bay Tree Problems — Brown Leaves, Scale, and Cold Damage

A bay tree (Laurus nobilis) is one of the most useful plants in the herb garden — evergreen, fragrant, and long-lived when well cared for. But bay trees can suffer from a handful of persistent problems, most of which are easily managed once you know what to look for. Brown leaves, sticky residue, yellow spots, and frost-scorched foliage are the most common complaints.

Frost and Wind Scorch — Brown Tips and Edges

Bay trees are not fully hardy in all climates. A hard frost, prolonged cold wind, or rapid temperature drop can scorch the leaf edges, turning them brown and crispy. The damage is cosmetic and the tree will usually recover — new growth in spring pushes through and the scorched leaves gradually drop. Remove the worst-damaged leaves in spring, give the tree a light feed, and protect it the following winter. Pot-grown bay trees are particularly vulnerable and should be moved under cover or into an unheated greenhouse when temperatures are forecast to fall below -5°C for more than a few days.

Bay Sucker — Yellowing Leaves with Curled Edges

Bay sucker (Trioza alacris) is a tiny insect pest that attacks the growing tips of bay trees. Infected leaves curl tightly at the edges, turn yellow, and become thick and waxy. You may find yellow-green nymphs hidden inside the curled leaves. Remove and destroy affected shoots as soon as you spot them. Repeat inspection every few weeks through the growing season as bay sucker overwinters and attacks new growth each spring. There is no chemical control approved for food-use plants, but physical removal is effective.

Scale Insects — Sticky Leaves and Black Mould

Brown or soft scale insects appear as small brown or white waxy lumps on stems and the undersides of leaves. They excrete sticky honeydew that coats the leaves, leading to a secondary infection of black sooty mould fungus. The mould itself does not harm the tree but blocks light from reaching the leaf. Wipe the scales off with a damp cloth or cotton bud dipped in rubbing alcohol. For heavy infestations, use a horticultural oil spray (thoroughly coating all stem and leaf surfaces) in spring when the crawlers are active.

Root Rot in Containers

Bay trees grown in pots are susceptible to overwatering and the resulting root rot, especially in winter when the tree is barely growing and water sits in the pot for extended periods. Ensure pots have drainage holes and raise them on feet to prevent the base sitting in water. In winter, reduce watering to once every two to three weeks. If the tree shows sudden wilting, yellowing, or collapse despite moist soil, remove it from the pot, inspect the roots, and trim off any rotted sections before repotting in fresh compost.

Leaf Spot Diseases

Yellow or brown spots on bay leaves can indicate fungal leaf spot diseases, which are more common in wet summers or when leaves stay wet overnight. Improve air circulation by thinning dense foliage, water at the base rather than overhead, and remove affected leaves promptly. In most cases the tree recovers without treatment once growing conditions improve. A copper-based fungicide can be used for severe cases, applied according to label instructions.