Squash bug
Anasa tristis
also called Anasa bug
Flat gray shield bugs that drain squash and pumpkin vines until whole runners wilt and blacken. Turn the leaves weekly from midsummer and crush the bronze egg clusters before they hatch.
How to know it
A flat, hard-backed bug about 15 mm long, dark gray-brown above with orange-and-brown barring along the edge of the abdomen, and a sharp sour smell when squashed. The nymphs look like a different insect entirely — round, pale gray-green, black-legged, moving in crowds — and the eggs are neat bronze ovals laid in a tidy V between the veins on a leaf underside.
What you'll see
- Bronze, almost metallic egg clusters glued in angular rows on the underside of the leaves.
- A whole runner wilts between morning and evening, then dries to brown and stays attached.
- Crowds of gray nymphs scatter under a leaf or a board when you lift it.
- Yellow speckling that runs together into dead patches across the older leaves.
- Fruit stops sizing and the vine gives up long before the first frost would have taken it.
Where it comes from
The adults overwinter under leaf litter, boards and vine debris, then walk into the patch as soon as the squash is up and start laying in early summer. One generation a year in the north and two in the south, with all stages present at once by August — which is why the population seems to arrive rather than build.
Worst on winter squash and pumpkin, in patches grown in the same corner year after year with a mulch of straw or old vine left down. Hot, dry summers speed the nymphs along, and no-till beds with plenty of ground cover give the adults the winter shelter they need.
Dealing with it
- Turn leaves twice a week from the moment the vines run and scrape the egg masses off with a thumbnail or a strip of tape.
- Lay a board or a shingle flat beside each plant overnight; the adults gather under it and can be tipped into soapy water at dawn.
- Hand-pick the adults in the cool of morning — they are slow then and hide on the stem side away from you at midday.
- Spray insecticidal soap directly onto young nymphs only; it does nothing to an adult, whose back sheds it.
- Pull and bin a vine that is already collapsing rather than nursing it — it is a nursery now, not a crop.
Keeping it out
- Clear every scrap of vine and mulch from the squash bed in autumn instead of leaving winter quarters.
- Rotate cucurbits to a different corner and put a season between them.
- Cover young plants with fine mesh until the first female flowers open, then lift it for the bees.
- Grow butternut and other Cucurbita moschata squashes where pressure is chronic — they suffer far less than pepo types.
- Keep the ground around the plants bare and open in midsummer so there is nowhere to shelter at your feet.
What it goes for
Pumpkins and winter squash above all, then courgettes, marrows, cucumbers and melons.
Who hunts it for you
- Assassin bugReduviidae A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be. Grow to recruit it: Dill,Fennel,Goldenrod,Sweet alyssum,Tansy,Yarrow
- Praying mantisMantidae A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors. Grow to recruit it: Cosmos,Fennel,Sunflower
- Tachinid flyTachinidae Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies. Grow to recruit it: Cilantro,Dill,Feverfew,Parsley,Sweet alyssum
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com