Pea and bean weevil

What you are looking at

Neat semicircular bites taken out of the edges of pea and broad bean leaves, evenly spaced all the way round so the leaf looks scalloped. Nothing else in the bed is touched.

The insect is a dull grey-brown weevil about 5 mm long with faint pale stripes running along its back and the long snout weevils have. It feeds at night and in dull weather, and when you disturb the plant it drops to the ground and stays motionless, so people see the damage for weeks before they see the animal.

An established plant covered in notches goes on to crop perfectly well.

The notching is not the damage

The scalloped leaves are what brings people to this page and they are close to irrelevant.

A pea or a broad bean past the seedling stage has far more leaf area than it needs, and the notches take a small fraction of it from the margins, where the loss costs least. Plants notched all over from top to bottom set a normal crop.

There are two situations where it does matter, and neither is the one people worry about.

The first is a seedling. A plant with two or three small leaves that loses most of them is checked or killed outright, so a cold slow spring in which peas sit at the two-leaf stage for a fortnight is when losses happen.

The second is underground, and it is invisible. The larvae hatch and burrow down to feed on the root nodules, the swellings where rhizobium bacteria fix nitrogen from the air for the plant. A heavy larval population hollows those out and the plant loses its own nitrogen supply.

That shows above ground as pale, stunted, slow growth rather than as anything you could attribute to an insect. Where a crop is notched and also pale, lift a plant and wash the roots, because empty or missing nodules turn a cosmetic problem into one worth feeding the crop over.

Timing is the whole of the control

The adults spend the winter in field margins, hedge bottoms and rough grass, and fly into legume crops in spring as the temperature climbs.

A broad bean sown in autumn is a substantial plant by the time that flight arrives and never notices it. The same variety sown in March meets the flight as a seedling. Moving the sowing date is therefore worth more than anything applied to the crop, and raising plants in modules to set out with several leaves already made achieves the same thing on a garden scale.

Fleece over a newly sown row covers the vulnerable weeks and comes off before flowering, since broad beans and peas want the pollinators.

What to do about it

Ignore the notching on an established plant.

Sow broad beans in autumn where the climate allows, or raise plants in modules and set them out well grown.

Fleece a newly sown row and take it off before flowering.

Lift and wash a plant where the crop is pale as well as notched, and look at the nodules.

Feed the crop where the nodules have been eaten out.

Rotate peas and beans off the same ground for a few years.

Keep the rough margins that support the ground beetles.

What it gets mistaken for

Vine weevil notches evergreen shrubs and pot plants irregularly rather than legumes evenly.

Slugs make ragged holes anywhere on the leaf and leave slime.

Caterpillars leave larger irregular holes and dark pellets of frass.

Flea beetles pit the leaf surface with round holes and jump when disturbed.

Capsid bugs leave small brown-edged holes in puckered distorted growth.

Bruchus bean weevils are a different insect entirely, developing inside stored dried beans and leaving round exit holes.