Plum Curculio
Conotrachelus nenuphar is a small, mottled brown weevil, 5 - 6 mm long, with a distinctive curved snout and four bumps on its back. Adults emerge from overwintering sites around apple petal fall and feed on and lay eggs in young developing fruit. After egg-laying, the female cuts a crescent-shaped scar around each egg site, a distinctive identification mark. The larva develops inside the fruit, causing it to drop prematurely.
Symptoms to Look For
- Crescent-shaped or C-shaped scars cut into young fruit skin shortly after petal fall
- Small sunken feeding pits or dimples on fruit surface, sometimes oozing a small amount of juice
- Premature fruit drop in May and June, fruit noticeably small and hard inside
- White legless grubs found inside prematurely dropped fruit
- Misshapen, scarred, or corky areas on fruit that did not drop but carried eggs that hatched
Affected Plants
Organic Solutions
Kaolin Clay Spray
Begin applying kaolin clay at first pink (before flowers open) and continue through the 4 - 6 weeks after petal fall when adults are most active and egg-laying. Coat all fruit and foliage thoroughly and reapply every 7 days and after rain. The particle film physically deters weevils from feeding and laying eggs on coated surfaces.
Trunk Tapping and Collection
Weevils drop from trees when disturbed. Lay a white sheet or tarpaulin under the tree and strike branches firmly with a padded mallet early in the morning when adults are sluggish with cold. Collect and destroy fallen weevils. Most effective in the 2 - 3 weeks after petal fall when adults are concentrating on young fruit.
Entomopathogenic Nematodes
Apply Steinernema carpocapsae or Heterorhabditis bacteriophora nematodes to soil under trees in midsummer when larvae and pupae are present in the top layer of soil. Keep soil moist for 2 weeks after application. Nematodes parasitise larvae and reduce the overwintering adult population for following seasons.
Remove Dropped Fruit
Collect and destroy all fallen fruit every 2 - 3 days from petal fall through June. Most dropped fruit contains larvae that will mature, burrow into soil, and pupate. Destroying fallen fruit is one of the highest-impact low-cost interventions available.
Prevention
- Begin kaolin clay applications before flower opening rather than waiting for damage - adults arrive at petal fall and egg-laying starts immediately
- Collect and destroy all fallen fruit every 2 - 3 days from mid-May through June - this significantly reduces the soil-overwintering adult population for the following year
- Apply nematodes to the soil under trees in midsummer - consistent annual applications build up a persistent population of natural larval enemies in the soil
- Cultivate the soil under trees shallowly in late autumn to expose overwintering pupae to frost and birds
Garden, by Willowbottom recommends only organic, wildlife-friendly solutions. No synthetic pesticides, no harmful chemicals - ever.