Cabbage looper
A pale green caterpillar that arches its back as it walks and chews ragged holes in cabbage-family and other leafy plants.
Also known as: Looper caterpillar, Inchworm
Symptoms and identification
Ragged holes are chewed in leaves, leaving veins, and dark droppings are left on foliage and in heads. Light green caterpillars with white lines along the sides move in a looping, inchworm-like way and are 3 to 4 cm long when mature.
Causes
Night-flying brown moths lay single round eggs on leaves. In warm weather several generations develop, and numbers build up from mid to late summer.
Organic treatment
Hand-pick caterpillars, and spray Bacillus thuringiensis (Bt) on young larvae in the evening, repeating after rain. Spinosad products allowed for organic use work too.
Prevention
Cover plants with fine mesh from planting, check leaves from early in the season and keep weeds around the garden under control. Natural enemies such as parasitic wasps help, so avoid broad-spectrum sprays.
Chemical treatment (use with care)
Use an insecticide labelled for loopers on that crop, following the label and harvest wait.