Pea & bean weevil
Sitona lineatus
Neat U-shaped notches all round the edges of pea and broad bean leaves. It looks dramatic and matters only to a seedling.
How to know it
A small grayish-brown weevil 5 mm long with faint pale stripes down the back and a short blunt snout, which drops to the ground and plays dead the instant it is disturbed. The damage is far more distinctive than the insect: neat, regular, semicircular bites taken from the leaf margins, giving a scalloped edge.
What you'll see
- Regular U-shaped notches eaten from the edges of pea and broad bean leaves.
- Damage worst on the outer leaves and on the earliest sowings.
- Seedlings checked or killed where the notching removes most of the small leaf area.
- Larvae feeding on the nitrogen-fixing root nodules, found when a plant is lifted.
- Weevils dropping off and vanishing into the soil when you look for them.
Where it comes from
Adults overwinter in hedge bottoms, leaf litter and old legume ground and move into pea and bean sowings very early in spring. They lay in the soil; the grubs feed on the root nodules through early summer, and new adults emerge in midsummer. One generation a year.
Cold, slow springs are the worst, because the seedlings grow slowly while the weevils feed. Once the plants are away and growing hard, the notching is irrelevant.
Dealing with it
- Get the seedlings growing fast: water, protect and warm them, and they will outgrow it in a fortnight.
- Cover early sowings with fleece or fine mesh until the plants are 15 cm tall.
- Sow a little thicker so a few losses in the row do not matter.
- Do not spray. The damage almost never justifies it and it is over quickly.
- Start peas and beans in modules and plant out at a decent size.
Keeping it out
- Sow a little later, or start under cover, so the seedlings meet the weevils already growing strongly.
- Rotate legumes away from last year ground.
- Clear old pea and bean haulm at the end of the season rather than leaving it as winter shelter.
- Warm the soil with fleece before sowing.
- Encourage ground beetles, which take a surprising number of the adults.
What it goes for
Peas, broad beans, French beans and sweet peas, plus clover, vetch and lupins.
Who hunts it for you
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com