Brassica Pests - Cabbage Aphids
Winged cabbage aphid adult with nymphs on a
damaged cole crop leaf.
Cabbage aphid colony on a kale leaf.
Cabbage infested with aphids.
Adult & nymph: Green-gray in color with a white waxy coating and short cornicles (two “tail-pipes” on the tail-end of the abdomen). Adults may be winged or wingless. Cabbage aphids form dense colonies on undersides of leaves of broccoli, Brussels sprouts, cabbage, cauliflower, kale, and other related cole crops . Aphids prefer to feed on young leaves and flowering structures; they can occur deep inside the heads of Brussels sprouts and cabbage.
As aphid densities increase or plant conditions deteriorate, winged adults are produced, and they migrate to alternate hosts including vegetables and weeds during the summer. Winged adults colonize plants by depositing live young on one plant, and then fly to a nearby host plant. Aphids reproduce asexually (parthenogenesis) during the spring and summer, and sexually in the late summer and fall. Many overlapping generations occur each year.
Aphids feed by inserting their piercing-sucking mouthparts into plant tissue and removing the sap. Aphid feeding may cause yellow spots, water stress, and reduced plant growth rate. If aphid feeding is prolonged, or heavy infestations occur, reduction of yield may result. Leaf distortions may also occur, though this is more common on primary hosts. Aphids excrete a sticky substance known as honeydew on which sooty mold can grow.
Cabbage aphids can overwinter as eggs on Brussels sprouts, cabbage, and kale. It is important to thoroughly destroy host plant debris through tillage and/or rouging.
- Avoid excess fertilization. Aphid densities tend to be higher on plants that have an excess of nitrogen fertility
- Use mulches or row covers. Metallized/reflective mulches and row covers can help reduce aphid populations on vegetables by interfering with the ability of winged aphids to find plants.
- Don’t plant vegetable crops near overwintering hosts such as peach or nectarine trees.
- Remove/destroy plant debris. Disking fields immediately after harvest will destroy alternate host plants and reduce available aphid and virus sources.
- Maintain healthy, vigorous plants. They are more tolerant to attack by aphids.
- Plant susceptible crops upwind. Planting upwind from infested plants decreases aphid migration into the crop since aphids are blown downwind
Many aphids have developed resistance to a number of different insecticides, including some synthetic pyrethroids, carbamates, and organophosphates. Additionally, when selecting insecticides, choose those that are less damaging to natural enemies of aphids and other insects in the crop.
Natural enemies include lady beetles, lacewings, syrphid flies, and parasitic wasps. These and other predators play a major role in the natural suppression of aphids.