Most people prefer ice cream over broccoli? Insects also have a sweet tooth. They prefer some plants over others. Trap crops are plants which attract insects away from desired food crops. First step is to identify which insects are causing the biggest problem. Then select a trap plant for that insect. Destructive pest insects are most attracted to plants in the reproductive stage of growth – flowering, fruiting, or setting seeds. Trap crops should be planted before desirable food crop, so they are flowering first. Depending on the plant this is usually a couple of weeks. After the insects attack the trap crop you can control them by removing the leaves or use an organic pesticide.
In a study conducted by the University of Missouri, Blue Hubbard squash was found to be an effective trap crop to control squash vine bores and squash bugs. Two-week old seedings of Blue Hubbard squash were placed at the end of rows for the cash crop. The insects were then controlled by removing the plant or treating with insecticides.
Nasturtiums are a good companion plant for the garden. They attract Aphids (blackfly, greenfly, whitefly), Flea beetles, Cucumber beetles, Squash vine borer insects and butterfly larvae away form other plants. It is available in climbing and bushy forms. All parts of the plant are edible raw. The taste is peppery, spicy and hot. The flowers are less hot than the leaves.
Tat Soi is used in the Brunswick County Master Gardener Edible Garden as a trap plant. It attracts flee beetles. It is in the mustard family and has a flavor similar to Bok Choi. It can be grown from transplants are directly from seeds.
Marigolds are commonly used in gardens to deter insects. While the data is lacking as to whether marigolds actually deter insect pests, they definitely attract beneficial insects such as lacewings, ladybeetles, and parasitic wasps. Recent research indicates that marigolds contain compounds toxic to root knot and other plant-parasitic nematodes (microscopic round worms that damage plant roots).
More information. Trap crops are a form of Integrated Pest Management (IPM). More information on IPM can be found in the NC Extension Gardener Handbook which is available at NC Extension Gardener Integrated Pest Management. Photos from NC Extension Gardener Plant Toolkit.