Plum curculio
Conotrachelus nenuphar
A snouted weevil that cuts a crescent scar into young stone and pome fruit and lays inside it. Tarp-and-shake at dawn through the four weeks after petal fall.
How to know it
A dark, warty, hump-backed weevil 5 mm long with a curved snout, mottled brown and gray, that plays dead and drops when disturbed. The damage identifies it long before the insect does: a crescent-shaped cut, like a small letter D lying on its back, in the skin of a fruit the size of a marble.
What you'll see
- Crescent scars on young plums, cherries, apples and peaches within a month of petal fall.
- Heavy fruit drop in early summer, well beyond the normal June drop.
- Fallen fruitlets with a grub inside and a brown tunnel to the stone.
- Corky, deformed apples where the fruit grew on past the scar rather than dropping.
- Rot spreading from every scarred fruit that stays on the tree.
Where it comes from
Adults overwinter in leaf litter and hedgerows, walk and fly into the orchard at petal fall, and feed and lay for four to six weeks. The grub develops inside a fruitlet, which usually drops, then pupates in the soil; the new adults appear in late summer and feed on fruit before finding winter quarters. One generation in the north, two in the south.
Worst in gardens bordered by woodland or scrub, which is where the adults spend the winter and the season between. Warm, still evenings after petal fall bring the heaviest movement into the trees.
Dealing with it
- Spread a sheet under the tree at dawn and jar the branches with a padded pole — the weevils drop and play dead, and can be tipped into soapy water. Repeat every few days for a month after petal fall.
- Pick up and destroy every dropped fruitlet twice a week; that is where the next generation is.
- Thin the crop after the drop finishes and take out every scarred fruit while thinning.
- Run poultry under the trees if you keep them; they clear the dropped fruit and the pupae in the soil.
- Bag individual apples once the fruit is walnut-sized where the tree is small enough to make it practical.
Keeping it out
- Keep the ground under fruit trees clear of leaf litter and long grass over winter.
- Clear wild plum, cherry and hawthorn from the boundary if you can — they are the reservoir.
- Plant fruit trees away from the woodland edge where the choice exists.
- Watch the calendar rather than the insect: control is a four-week window from petal fall and nothing outside it helps.
- Accept a proportion of scarred fruit on a large tree and concentrate on keeping the drops picked up.
What it goes for
Plums, cherries, peaches and apricots first, then apples, pears and quince.
Trouble it brings with it
Who hunts it for you
- Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
- Ground beetleCarabidae Fast, glossy night hunters that patrol the soil surface for slugs, cutworms, and root-fly larvae. Give them daytime cover — thick perennial edges, stepping stones, a log — and skip the tillage that wrecks their burrows. Grow to recruit it: Lavender,Mint,Thyme
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com