Steinernema carpocapsae
Entomopathogenic nematode- Rate
- 250k–500k /m² (≈1 billion per acre at the low end)
- Temp
- 14–34 °C; best 19–31 °C
- Best for
- Squash blossoms only; not small-flowered cucurbits
Pest
Pickleworm
Diaphania nitidalis
The short answer
The caterpillar of a tropical moth that routinely survives the winter only in south Florida, and perhaps south Texas. Each summer the moths spread north. They flood north Florida by early June, but in the Carolinas damage often does not start until August or September, and in some years they get as far as Michigan and Connecticut. The larvae feed in the flowers and bore into the fruit of squash, cucumber, cantaloupe and pumpkin, and summer squash is the favourite. Once a larva is inside, it is beyond the reach of Bt and hard to detect, so commercial growers spray preventively. UF/IFAS says none of its natural enemies reliably suppress damage. The practical garden controls are early planting and covering the plants.
hero macro · larva at its entry hole in a squash fruit
Late-instar Diaphania nitidalis beside its entry hole in a summer squash, frass pushed out at the opening. Photo: pending.
Identification
Young larvae are nearly white with many dark grey or black spots, and they lose the spots at the last moult. Full-grown larvae reach about 1 inch (2.5 cm), are often green but vary with what they have eaten, from white to bronze, and turn a dark copper colour before pupating. The moth is distinctive, with a wingspan of about 1.2 inches (3 cm). Both pairs of wings have a semi-transparent yellow centre with a purplish sheen and a dark brown border, and there is often a brushy tuft at the tip of the abdomen. Moths fly only at night.
Its close relative the melonworm, Diaphania hyalinata, has white wings edged in brown. Its larvae carry two white stripes along the body and mostly eat the leaves, stripping them to the veins, rather than boring into the fruit. Because of that, UF/IFAS says Bt can work very well on melonworm, which is not true of pickleworm.
Easily confused with
- MelonwormAlso a pestThe moth’s wings are white edged with dark brown, and the full-grown larva has two white stripes down its body. It mostly eats leaves, where pickleworm bores into flowers and fruit.
Damage symptoms
Young larvae feed in the blossoms, and in large-flowered squash they may never leave them, moving from flower to flower and wrecking the plant's ability to set fruit. More often they bore into the fruit, and fungal or bacterial rot follows. When flowers and fruit are gone, they attack the vine tips. On cantaloupe they tend to scar the rind rather than burrow in, which is why they are sometimes called rindworms.
- A small round hole in the fruit with frass pushed out of it
- Caterpillars in flower buds and open blossoms
- Few fruit setting, because the flowers have been eaten
- Fruit rotting from the entry hole
- Vine tips bored and dying late in an attack
Lifecycle & degree days
The whole cycle takes about 30 days, so generations overlap. There are about four a year in Georgia and two or three in North Carolina. It routinely survives the winter only in south Florida and perhaps south Texas, and has been found overwintering as far north as central Florida in mild winters, so each summer's attack comes from moths spreading north. That is why it arrives later the further north you are, and why an early planting can often be partly harvested before it arrives.
- Egg to adult
- About 30 days
- Larval feeding
- About 14 days, five instars
- Generations / yr
- About 4 (Georgia); 2–3 (North Carolina)
- Arrives
- North Florida early June; Carolinas often not until August–September
- Overwinters
- Routinely only in south Florida, perhaps south Texas
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Host crops
It feeds on wild and cultivated cucurbits. Summer squash is the most preferred and most heavily damaged, winter squash is also a good host, and pumpkin is variable. Cucumber, gherkin and cantaloupe are attacked but not preferred, and watermelon is rarely touched. Creeping cucumber is an important wild host. No truly resistant cultivars are known.
Monitoring & action thresholds
Action threshold
No usable threshold
UF/IFAS says the pest is very hard to scout. The eggs are tiny, the moths fly at night and are not drawn to light traps, and pheromone lures are not sold. Commercial growers where damage is likely therefore spray preventively from the start of flowering or fruiting through harvest. The most reliable sampling unit found in research is the large green male flower bud.
From midsummer, check the large green male flower buds and open blossoms for small spotted larvae, and look for holes with frass in the fruit. Know your region's usual arrival date: early June in north Florida, and often not until August or September in the Carolinas.
Beneficial
Biological control
UF/IFAS lists ground beetles (Calosoma and Harpalus), a soldier beetle and fire ants among the important predators. Parasitoids include several braconid wasps (Apanteles, Hypomicrogaster and Pristomerus), ichneumonids and unidentified trichogrammatid wasps. It is candid that none of these reliably suppress damage. The one biological control UF/IFAS reports working is the nematode Steinernema carpocapsae, which suppressed pickleworm injury in squash in a 1994 study. It works because the nematodes survive inside large squash blossoms and kill young larvae before they bore into the fruit. UF/IFAS says it is probably ineffective in cucumber and less effective in cantaloupe, whose small open flowers leave the nematodes exposed to sunlight, which kills them quickly. Bt kills pickleworm, but UF/IFAS usually does not recommend it, because the larvae feed out of reach inside flowers and fruit.
Cotesia congregata and other Braconidae
Braconid wasps- Kind
- Wild — attract it
- Best for
- Wild larval parasitoids; not reliable
Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Wild predators; not reliable
Cultural controls
Timing and exclusion do more in a garden than any spray.
- Plant squash, cucumbers and melons early; early plantings may escape damage, or let you harvest part of the crop before the moths arrive
- Cover small plantings with row cover or screen; the moths fly at night and bees by day, so the cover can come off for pollination
- Squash has been tried as a trap crop to draw pickleworm off cantaloupe, but the old trials disagree on whether it works
Chemical, last resort
Spraying during bloom kills the bees that pollinate cucurbits. UF/IFAS advises short-residual products applied late in the day, when bees are not foraging.Check any product before it goes on. Open the compatibility matrix →
- Bt kurstakiREI 4 h
- MethoxyfenozideREI 4 h
- ChlorantraniliproleREI 4 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UF/IFAS EDIS EENY164, Pickleworm, Diaphania nitidalis (Capinera, rev. 11/2023)
UF/IFAS EDIS ENY-460, Insect Management for Cucurbits (rev. 07/2020)
UC IPM, Relative Toxicities of Insecticides Used in Tomatoes to Natural Enemies (09/16)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Pickleworm by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.