Destructive Insect Series - Diamondback Moth

Found wherever cabbage is grown, the diamondback moth deposits a single egg or groups of eggs usually on the underside of foliage. In 5 to 6 days, larva emerge. They are colorless but as they develop, they turn green. They leaf mine for food and because they are so small, it often goes unnoticed and because they emerge from their eggs on the bottom of the foliage, that is where they feed. The result is irregular patches of damage, and the upper leaf epidermis is often left intact.

While in the pupa stage, they are in loose silk cocoons for about 8 days on the outer or lower foliage. This can also occur within the heads of broccoli and cauliflower. As adults, they are weak fliers aided by the wind to carry them long distances. They stay close to the ground and fly in short bursts if not helped along by a good breeze. They do not handle cold weather well and die off, but they re-invade cold winter areas in the spring aided by southern winds.

Plant damage is caused by the larva. They are very small and can be very numerous. The average female lays about 150 eggs during her 10 day cycle and the entire life cycle lasts about a month.

The tiny larva feed on cruciferous vegetable crops: broccoli, cauliflower, cabbage, brussel sprouts, Chinese cabbages, kale, collards, kohlrabi, mustard, radish, turnip, and watercress, with collards being a particular favorite.

They are susceptible to viruses and fungus diseases and are also are often killed by the parasitoids such as Microplitis plutellae. Another major killer of these eggs and larva is rain.

Systems where sprinklers are raining down on the garden will have fewer of these pests. Crop diversity helps to keep the numbers down as well. Planting cruciferous crops with other crops between will help to prevent the spread.

Good luck!