Plum moth
Grapholita funebrana
Pink caterpillars feed around the stone inside ripening plums. Use pheromone traps from early summer and thin overcrowded fruit.
How to know it
A small gray-brown moth flying at dusk in June and July. The caterpillar is a distinctive dirty pink with a brown head, coiled in a mess of frass in the flesh around the stone — usually discovered when the plum is bitten into.
What you'll see
- Plums coloring and ripening noticeably early, then falling.
- A small entry hole near the stalk with a bead of clear gum or brown frass at it.
- Pink caterpillars and wet frass in the flesh around the stone.
- Damage confined to the fruit — leaves and shoots stay perfectly healthy.
- A crop that looks ready a fortnight before the neighbors’ tree, for the wrong reason.
Where it comes from
Caterpillars overwinter in cocoons under bark and in crevices, pupating in spring. Moths fly from June, laying single eggs on developing fruit; the caterpillar bores in, feeds around the stone for a month, then leaves to spin up. One generation in most years, occasionally a partial second.
Warm calm evenings during the June and July flight period. Heavy, unthinned crops on old trees with plenty of bark shelter suffer worst.
Dealing with it
- Hang pheromone traps from late May, one per tree, both to catch males and to time everything else.
- Thin the crop in June — it improves the fruit and removes eggs and young caterpillars with the thinnings.
- Pick up and destroy fallen fruit as it drops, before the caterpillars leave it.
- Do not compost infested plums; the caterpillars simply walk out of the heap.
- Encourage tits and treecreepers, which work the bark for overwintering cocoons.
Keeping it out
- Clean loose bark and clear crevices on old plum trees in winter.
- Keep the ground under the tree clear of fruit and litter all season.
- Trap consistently every year rather than in the bad years only.
- Grow later varieties where the pest is severe, which can escape the main flight.
- Avoid leaving windfalls in grass, where the caterpillars pupate undisturbed.
What it goes for
Plums, damsons and gages; occasionally sloes and cherry plums.
Trouble it brings with it
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com