Friday, July 27, 2012

Guide to Identifying and Controlling Imported Cabbageworms Organically

Cabbageworms (imported) are found throughout the U.S. and Canada. After invading the garden and chewing through the leaves of plants, they leave behind large holes and piles of dark droppings called frass; 2 telltale signs the garden pests have arrived. Fortunately for gardeners, there are 6 ways to control imported cabbageworms organically.

How to Identify Imported Cabbageworms

Adult Cabbageworms: Adults are white butterflies with black-tipped wings. Their forewings have 1 - 2 black spots on them and their wingspan measures about 1 ½ inches. As adults, cabbageworms continue to putter around the garden.

Larvae: Cabbageworm larvae are green and velvety. In the larval stage, these garden pests are in the form of caterpillars measuring about 1 1/4 inches long. They have a single, yellow stripe that runs down their backs.

Eggs: Eggs are yellow in color and cone-shaped. They can be found on the undersides of plant leaves.

When Imported Cabbageworms Attack

Adult cabbageworms come out in late spring to lay their eggs on the undersides of leaves. When the eggs hatch into caterpillars, they feed for 2 - 3 weeks on plant leaves, typically on the undersides. Next, they pupate, turning into butterflies a short 1 - 2 weeks later. These garden pests produce from 3 - 5 generations a year.

Plants Cabbageworms Attack

  • Cabbage Family Plants (broccoli, cauliflower)
  • Nasturtiums

How to Identify Cabbageworm Damage

Look for large holes that have been chewed through the leaves of plants in the cabbage family as well as piles of droppings (frass). Watch for damage on broccoli and cauliflower florets as cabbageworms will borrow through these as well.

Image: Patrice Beaulieu

6 Ways to Control Imported Cabbageworms Organically

1. Floating Row Covers: Cover plants cabbageworms attack with floating row covers. These prevent adult garden pests from laying their eggs.

2. Purple Cabbage Varieties: Plant these; they are less attractive to imported cabbageworms.

3. Sticky Traps: Place these near plants cabbageworms attack, especially those where eggs and caterpillars have been found. The traps will catch a good majority of butterflies.

4. Handpicking: Bring a bucket or bottle of soapy water out to the garden. Look on both sides of leaves on cabbage family plants and handpick eggs and caterpillars.

5. Garden Clean Up: In the fall, remove all plant debris from the garden to prevent pupae from over wintering in the soil.

6. Attract Good Bugs: Good bugs, like spined soldier bugs, green lacewings and syrphid flies all feed on cabbageworm larvae and eggs and are a great way to control cabbageworms organically. Spined soldier bugs are attracted to pollinating plants such as goldenrod, hydrangeas and milkweed.

Green lacewings are attracted to plants such as dill, caraway, dandelion, angelica, cosmos, sunflowers, goldenrod, and sweet alyssum. To water lacewings (they are delicate) and keep them in the garden, place a shallow pan with a layer of gravel on the bottom in the garden and then fill with a little water. This provides them with a place to drink without drowning.

Attract syrphid flies to the garden by planting pollen and nectar, providing plants like wild mustard and alyssum. Surround the garden with tall, flowering plants like sunflowers to provide a windbreak for syrphid flies.

Controlling imported cabbageworms organically is a multi-season task. Begin in the fall by removing all dead plants from the garden, especially those that have been attacked by garden pests. Do a walk-through of the garden and inspect plants for eggs and larvae. Get a head start on controlling the pests by handpicking them from the first time they appear.

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 Reference: Rodale Organic Gardening (2001). Basics:Pests Volume 7. Rodale Inc.

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