As they flit and flutter around the garden, butterflies are a delight to watch. However, some of these beauties can lead to quite a bit of damage to your garden. One innocent-looking offender is the cabbage white butterfly, also known as the imported cabbageworm butterfly.
When it's time for the female cabbage white butterfly to lay her eggs, she seeks out plants known as crucifers, Brassica family vegetables such as cabbage, mustard, broccoli and kale. Then she deposits her eggs on the undersides of leaves, where wormlike larvae hatch two to three weeks later.1 While the adult butterfly feeds on nectar from flowers, its newly hatched larvae seek other food. Known as imported cabbageworms or simply cabbageworms, these pests feed on cruciferous plants, chewing holes in leaves and boring into cabbages and ruining entire heads.
Cabbage white butterflies are native to Europe and Asia, but they are extremely common throughout the United States.2 Easily identified by their white color, male cabbage whites have one round black spot on their wings, while females have two black spots. Cabbage white butterflies and cabbageworms are present in gardens from early spring to late fall.1 Several generations occur each season and numbers build toward season's end, so gardeners must stay on guard the entire growing season to prevent cabbageworm damage to crops.
Dealing with the Cabbage Worm
The key to avoiding cabbageworm damage is to prevent the butterflies from laying eggs on plants. Once laid, the small eggs are easily overlooked. You may not know your garden has cabbageworms until you see them or their damage on your crops. While preventing damage is ideal, there is still hope for a harvest if you stop further damage promptly.
Prevention. The simplest way to prevent egg laying on your plants is to create a barrier around cruciferous vegetable plants as soon as you plant them. A tunnel-like row of simple hoops covered with protective fabric does the trick.3 Install hoops made from PVC piping, metal or bamboo, making sure the hoops are high enough so plants will not touch them when fully grown. Seed packets or plant tags list each plant's mature height. Secure hoop ends by pushing them deep in the ground.
After planting seeds or transplanting young plants, cover the hoops with fabric, allowing at least 6 inches of fabric to sit on the ground on all sides. Commercial row cover fabrics are popular options for protecting crops, but basic tulle is more economical and readily available from local fabric stores. Place rocks, poles, bricks or other heavy objects on top of the excess fabric to keep it in place. Row covers designed in this way make it impossible for the cabbage white butterfly to access your plants.
Managing cabbageworms. Once spring arrives, watch for the white butterfly in your garden. If you decided to delay row covers, installing them at this point is still helpful. However, once sighted, it is possible she has already laid eggs. Check diligently for signs of cabbageworms or their damage. Inspect the underside of all leaves before covering crops, and remove the cover occasionally to look for eggs or damage.