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Squash & zucchini

Most bugs on squash plants arrive in the same few weeks, between sowing and the first flowers. Striped cucumber beetles chew the seedlings. Squash bugs lay bronze egg clusters under the leaves. The squash vine borer moth lays at the base of the stem, and its larva tunnels inside until the whole plant wilts. Zucchini is a regular victim: in one study 53% of unharvested zucchini were infested, against 14.6% where the fruit was picked. Butternut is one of the few squashes that resists it.

Squash bug adults shrug off sprays and borer larvae are out of reach inside the stem, so garden control happens early and by hand: row cover until flowering, crushing egg masses, and slitting borers out of stems. From late summer, melon aphids and, in the South, pickleworm take over.

crop context · zucchini in flower, early summer

Common squash and zucchini pests, in the order you meet them

SEEDLINGS · MAY–JUNE

Striped cucumber beetle

Chews seedlings, flowers and fruit. Zucchini draws them; squash rarely gets their wilt.

ReleaseGround beetlesNothing to release — ground beetles and wolf spiders reduce numbers (JIPM)
JUNE–JULY

Squash bug

Speckled, then wilting leaves. Adults shrug off sprays; crush the bronze egg clusters.

ReleaseTachinid fliesWild — keep nectar plants near the crop, no broad-spectrum sprays
LATE JUNE–JULY · NORTH

Squash vine borer

A whole plant wilts in the sun, with wet, sawdust-like frass at the base of the stem.

ReleaseSteinernema carpocapsaePer package directions — no extension source gives a per-stem dose
JULY IN THE NORTH

Spotted cucumber beetle

Arrives too late in the North to do much harm. A bigger problem in the South.

ReleaseBraconid waspsWild — nothing to release (UF/IFAS lists braconids among its enemies)
LATE SUMMER

Melon aphid

Colonies under the leaves. Less of a pest on squash and pumpkin than on melons and cucumber.

ReleaseHoverfliesWild — attract adults with open flowers
JUNE–SEPT · SOUTH

Pickleworm

Bores into flowers and fruit. Summer squash is its favourite host.

ReleaseSteinernema carpocapsaeNo published rate — UF/IFAS cites a 1994 squash study without giving a dose

Season calendar

TEMPERATE US · OUTDOOR SQUASH · QUALITATIVE
JFMAMJJASOND
Striped cucumber beetleJan: QuietFeb: QuietMar: QuietApr: QuietMay: BuildingJun: Pest pressure highJul: BuildingAug: BuildingSep: QuietOct: QuietNov: QuietDec: Quiet
Squash bugJan: QuietFeb: QuietMar: QuietApr: QuietMay: BuildingJun: Pest pressure highJul: Pest pressure highAug: BuildingSep: BuildingOct: QuietNov: QuietDec: Quiet
Squash vine borerJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: BuildingSep: QuietOct: QuietNov: QuietDec: Quiet
Spotted cucumber beetleJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: QuietNov: QuietDec: Quiet
Melon aphidJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: BuildingSep: Pest pressure highOct: Pest pressure highNov: QuietDec: Quiet
Pickleworm (South)Jan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Nematodes (vine borer)Jan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: Release windowJul: Release windowAug: QuietSep: QuietOct: QuietNov: QuietDec: Quiet

Starter program

Squash has one release worth trying: nematodes at the stem base while vine borer eggs hatch. The trial results are mixed, so treat it as a supplement to row cover, not a replacement.

  1. AT SOWINGGround beetlesNothing to release. Keep the crop under row cover until it flowers, and leave the beetles somewhere to shelter.
  2. EGG HATCH · LATE JUNE–JULYSteinernema carpocapsaePer package directions. Spray the stem base and soil as vine borer eggs hatch. Injecting bored stems did worse than spraying in the South Carolina trials.
  3. SUMMERTachinid fliesNothing to release. Keep nectar plants near the vines and avoid broad-spectrum sprays; Trichopoda lays its eggs on large squash bug nymphs and adults.
  4. LATE SUMMERHoverfliesNothing to release. Keep open flowers near the bed and leave aphid colonies that already have larvae in them.

Setting up the garden

Squash pests are settled at sowing and in the first weeks of flowering.

Cover until the first flowers

Row cover keeps cucumber beetles, squash bugs and vine borer moths off young plants. Take it off once flowering starts so bees can pollinate.

Check under the leaves

Crush squash bug egg clusters as you find them. A board laid on the soil overnight collects adults to destroy in the morning.

Operate on bored stems

Slit the stem lengthways, kill the larva, and heap moist soil over the wound. Burying stem nodes along the vine lets it root beyond the damage.

Grow butternut if borers win every year

Butternut and other Cucurbita moschata squashes resist the vine borer. After harvest, clear old vines and debris where squash bugs overwinter, and till the bed to disturb borer cocoons in the soil.