🥒 Pickleworm
Diaphania nitidalis
It was ruining pickles before pickles were cool.
How to identify
Young caterpillars are yellowish-green with distinct black spots; older ones lose the spots and turn solid green, reaching about 3/4 inch. You'll find them boring into cucumber and squash blossoms, stems, and fruit — look for moist frass (bug poop) packed around tiny entry holes.
Damage signs
Larvae tunnel into blossoms first, then into young fruit, leaving hollowed, rotting cucumbers and squash with mushy entry wounds. Infested blossoms drop, so fruit never even forms — the plant flowers beautifully and produces nothing.
Plants it attacks
Cucumbers, summer squash, winter squash, pumpkins, melons
Non-chemical controls
- Keep floating row cover on from transplant until harvest, lifting only briefly for pollination — the moth lays eggs at blossom time, so covered blossoms stay clean.
- Inspect blossoms every morning and handpick any caterpillars; they're right there in the open flower, easy to spot and squish.
- Remove and trash every bored fruit immediately — each one is a nursery, and composting it just moves the nursery.
- Plant early-maturing cucumber and squash varieties to get your harvest in before pickleworm numbers explode in late summer and fall.
- Till beds in fall and again in spring to expose overwintering pupae in the soil and debris to predators and cold.
- Release Trichogramma wasps during flowering season; they parasitize the moth's eggs before caterpillars ever hatch.
Nerdy fact: Pickleworms are tropical moths that can't survive freezing winters — every spring, the moths migrate north from Florida like tiny snowbirds, and your cucumbers are the timeshare.
Still not sure this is your culprit? What’s Eating My Plant? narrows the suspects from what you actually see on the plant.