In the garden: Stocks, wallflowers and other ornamental brassicas
On Crops: All members of the cabbage family including cabbage, broccoli, brussels sprouts, collards
Worldwide in temperate climates
The diamondback moth is also called the cabbage moth, because it lays its eggs almost exclusively on cabbage family crops. Starting in spring, the moths lay eggs that hatch into tiny green caterpillars with forked tails, often in large numbers. They do not have the velvety skin texture of cabbage worms, which are a different pest. The caterpillars are less than ½ inch long with whitish heads and feet.
The larvae rasp holes in plant leaves that gradually enlarge to give the leaves a windowpane appearance. The caterpillars are found mostly on leaf undersides.
In areas where cabbage moth is a chronic pest, try making a small planting of cress each spring, and let the bugs have it. The adult moths will lay their eggs there rather than on your garden plants, and you can chop up the cress and compost it when it is loaded with larvae. Many gardeners also use protective row covers to exclude this and other pests from cabbage family crops.
Diamondback moths have become resistant to most pesticides, including Bt. Hand picking is a better option, and can make a big impact when you check your plants every day. Beneficial insects including many types of wasps and hornets harvest large numbers of immature larvae to feed to their young.
Diamondback moths can complete their life cycle within a 15-30 day period during the summer months. Avoid planting succession brassica crops when a diamondback moth infestation has occurred.