What has cut neat notches round the edges of my leaves?

These two look similar in a photograph and could not be more different in what they mean. One is a protected solitary bee taking nest material from a plant she does not otherwise harm. The other is the visible half of an insect whose larvae eat roots underground and kill container plants.

Step by step

1. Look at the edge of the cut with a lens or in good light.A leafcutter bee cuts with mandibles like scissors and the edge is smooth, continuous and clean, as if made with a punch. A weevil chews, and the edge of a weevil notch is minutely ragged and slightly torn.
2. Count the cuts and their shape.Leafcutter bee: one or two large, near-perfect circles or ovals per leaf, and only on a few leaves. Vine weevil: many small shallow scallops repeated along the margins of many leaves on the same plant.
3. Check which plant it is.Leafcutter bees strongly favour roses, wisteria, lilac and laburnum. Vine weevil adults favour evergreens with tough leaves — euonymus, rhododendron, camellia, bergenia, heuchera, primula and strawberry.
4. If it is a leafcutter bee, stop here.She is not eating the leaf, she is carrying the disc away to line a nest cell. She does not return in numbers, the plant is unharmed, and solitary bees are important pollinators in decline. There is no treatment and no need for one.
5. If it looks like weevil, go and look at night.Adult vine weevils are dull black, about 9mm long, with a long snout and a rough pitted back. They are flightless, active after dark, and hide by day under pot rims, in leaf litter and in the crown of plants. A torch an hour after dusk finds them.
6. Then check the compost, which is the point.Knock any nearby container plant out of its pot over newspaper and look for fat, creamy-white, C-shaped grubs about 10mm long with brown heads. That is what kills plants. The adult notching is cosmetic.
7. Treat the grubs rather than the notches.Nematodes watered into moist compost when it is warm enough are the main control, and containers are where they work best. Repotting a badly affected plant into fresh compost, washing the roots, removes the population directly.
8. Consider the other margin-feeders if neither fits.Pea and bean weevil cuts identical U-shaped scallops but only on peas and broad beans in spring, and is tolerable on anything past the seedling stage. Earwigs make more irregular ragged edges and are found by day inside rolled leaves and flowers.

Tips

• Leafcutter bee damage peaks in midsummer and stops. If the cuts stopped appearing, that is what it was.
• Vine weevil adults drop and play dead the moment a plant is disturbed. Hold a sheet of paper under the plant and shake it.
• A physical barrier of sticky grease band material around a pot rim stops flightless adults reaching the compost to lay.
• Every adult vine weevil in the UK is female and lays without mating, which is why populations build so fast and why removing individuals is worth doing.

Common mistakes

• Spraying a rose for leafcutter bee — There is no approved or effective treatment, the plant is not harmed, and you are spraying a pollinator on a plant she visits.
• Treating the notches and ignoring the pots — The notches cost the plant nothing. The grubs eating the roots below are what kills it, and by the time the plant wilts they have finished.
• Assuming a plant in the ground is safe — Vine weevil is worst in containers but does occur in beds, particularly in light soils and around strawberries and heucheras.

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