Decoy and Trap Crops
It may sound a bit crazy, but growing plants to attract pests
may be another way to use companion plants to your advantage. The trick is
to find a plant that the pest will prefer to your good stuff. The pests will
then be more likely to damage the decoy, and once the pests have congregated
on the trap crop, you can easily destroy them.
Before deciding that decoy plants are the answer to all of your pest management problems, make sure that you are aware of the problems they can cause first. The use of decoy plants is something that requires regular attention. It is not a quick fix to plant a few decoys and then assume that your garden will be perfectly protected while you lounge on the back porch with some iced tea and a good book. It takes advance planning and careful, continued observation. It takes up space in your garden without producing a "harvest" of food or beauty (although some can be beautiful). And, if you aren't careful about how you dispose of the pests, you could put them back in your garden or kill off beneficials.
Trap Crop Guidelines
Get the timing right! Don't wait until you see the first pest before you plant your decoy. It must be growing when the pests are out in force. If this is a once-a-year problem - for example, cabbage maggots and carrot beetles can be worst in the spring - a single planting of a trap crop may be enough to control them. But, if the pest is in action all summer, you may need to plant a succession of crops. Learn about the life cycles of your pests by checking previous years' notes, asking gardening neighbors, or checking out the various publications available through Cooperative Extension offices for help in finding out about your pests. Once you know when the problems are most likely to occur, you will be better able to plan your decoys.
Here's an example of how decoys can work to lure aphids away from your roses. As soon as the last spring frost passes, plant clumps of nasturtium seedlings beside your rose bush. It's important to start with seedlings, as you need the plants to be well-rooted before the first generation of aphids becomes a real problem. As soon as you find the aphids swarming on your nasturtiums, destroy the plants and pests promptly so that the aphids don't reproduce. Since aphids give birth to live babies, who will mature to reproductive age within 2 weeks, make sure you don't let an aphid trap go unobserved for 2 weeks, or you could multiply the problem instead of solving it. For continued trap cropping, sow nasturtium seed every 2 weeks until midsummer.
Closeness counts. Grow the trap plants as near as you can to the plant bothered by pests. Plant the traps beside ornamentals, in between rows in the vegetable garden, or intermingled in wide beds. Watch the traps carefully and be prepared to act when the trap has been "sprung".
When you find that your trap crop is infested, you have several ways to go about eliminated the pests. Do away with most of the pests, leaving a few for beneficial insects to dine upon. Pick off and destroy large, slow pests like tomato hornworms or cabbage loopers, unless they are covered with white cocoons indicating that the pests have been parasitized by benficials). Shake crawling pests like beetles and weevils off of trap plants in the cool morning or evening, when pests are moving more slowly, and catch them on the ground in a towel or sheet of paper. Pick or dump pests into a bucket of soapy water.
To trap tiny or fast moving pests, cover the entire plant gently with a plastic bag. (Watch out for the beneficials and release them if possible before sealing the bag. Use a twist tie to seal the bag opening around the plant stem. Then uproot and discard the bag, bugs and all!
Here are some trap crops you might want to try:Colorado potato beetles are attracted to black nightshade
Cabbageworms and harlequin bugs will swarm away from cabbage plants to mustard plants
Flea beetles and aphids are drawn to nasturtiums
Cabbage maggots will riddle radishes rather than broccoli, cauliflower, and cabbage