Common Herb Pests — How to Identify and Control Them

Herbs are generally more pest-resistant than vegetables, largely because their aromatic oils repel many insects. But they are far from immune — and when pests do strike, the fact that you are eating the leaves means you want to stick to organic and food-safe controls. The good news is that most common herb pests can be managed effectively without chemical pesticides.

Aphids — The Most Common Herb Pest

Aphids attack a wide range of herbs, including mint, parsley, dill, and fennel. They cluster on soft growing tips and the undersides of new leaves, sucking sap and excreting sticky honeydew that leads to sooty mould. Small infestations can be controlled by pinching off affected shoot tips or washing the insects off with a strong jet of water. For larger infestations, a spray of diluted insecticidal soap (or a few drops of washing-up liquid in water) applied to all leaf surfaces, including undersides, is effective and safe for edible plants.

Leafhoppers and Froghoppers

Leafhoppers are small insects that hop away when disturbed, leaving pale, mottled stippling on leaves — most noticeable on rosemary and sage. Froghoppers produce the familiar "cuckoo spit" (white froth) on stems in late spring and summer. Froghoppers rarely cause significant damage and can be removed by hand or with a jet of water. Leafhoppers in large numbers can stress plants; improve air circulation and reduce hiding places by removing dead leaves and debris around plants.

Vine Weevil — Container Plants at Risk

Vine weevil grubs are a serious problem for potted herbs. The cream-coloured grubs live in the compost and eat roots, causing sudden wilting and collapse — often the first sign you notice. If a pot-grown herb collapses without obvious cause, tip it out and inspect the root ball for C-shaped white grubs. Remove and destroy all grubs by hand. Prevention is more effective than treatment: use vine weevil-resistant compost containing nematodes, or apply a nematode biological control (available by mail order) to moist compost in late summer when soil temperature is above 5°C.

Caterpillars and Slugs

Large irregular holes in herb leaves usually indicate slugs, snails, or caterpillar feeding. Check for slugs at night with a torch, or in the early morning under pots and boards. Remove by hand and dispose of them away from the garden. Caterpillars are usually visible if you look carefully at the underside of leaves — pick off by hand. Copper tape around pot rims deters slugs and snails from climbing into containers. Iron phosphate slug pellets are safe around wildlife and food crops and can be used as a backup where slug pressure is severe.

Spider Mites on Herbs Indoors

Spider mites are tiny sap-sucking arachnids that thrive in hot, dry conditions — most commonly on indoor herbs in warm rooms. Look for very fine silk webbing on leaves and between stems, plus pale, stippled leaf surfaces. Increase humidity by misting the plants or placing them on a tray of damp pebbles. A spray of diluted neem oil or insecticidal soap applied thoroughly to all leaf surfaces (repeat every three to five days for three weeks) usually controls spider mite populations effectively.