Squash vine borer
Caterpillars of a day-flying moth that bore into the base of squash and pumpkin stems, causing sudden wilting.
Also known as: Melittia cucurbitae
Symptoms and identification
A healthy-looking squash plant suddenly wilts in the heat of the day. Holes near the base of the stem ooze sawdust-like frass, and slitting the stem reveals a fat, white caterpillar.
Causes
An orange-and-black clearwing moth lays eggs at the base of stems in early summer. It is a major pest of squash and pumpkins in North America.
Organic treatment
Slit the stem lengthwise, remove the larva, and bury the damaged section in moist soil so it roots. Inject Bt into stems where borers are active.
Prevention
Cover young plants with netting until flowering, wrap the lower stem in foil, and plant a second crop later in summer. Butternut squash is more resistant.
Chemical treatment (use with care)
Apply an insecticide labelled for vine borers to the base of stems during egg-laying, following the label.