Aphid infestations can quickly multiply. Actual cabbage plant damage occurs as the aphid feeds off of the plant, sucking out its juices. In it s wake, the cabbage aphid leaves a sticky coating on leaves known as honeydew or plant sap. This honeydew is a byproduct of the cabbage aphid s inability to digest all of the plant sugars. Ants are usually present, because they feed on this sticky substance.
Aphids can reproduce rapidly, so once infestation begins it is likely to get severe.
In the United States, cabbage aphids are active year round and their eggs are able to overwinter on plant debris. As soon as you note either the characteristic honeydew, or the actual presence of cabbage aphids, you should treat your cabbage family plants with diazinon or malathion containing insecticide. Make sure to repeat treatments of insecticide as long as you still see aphids. You can safely repeat treatments in seven day intervals. Also be sure to clean up any plant debris that has fallen in the garden, and at the end of the harvest to prevent overwintering.