Many vegetables are closely related and have the same pests. Some insects hibernate or lay eggs in or on the host plant. Do not grow the same kind of vegetable in the same place each year. Use related crops in a site only once every 3 or 4 years. Another type of crop rotation is to not follow root crops behind other root crops.
Crop rotation is most effective on insects that develop on a limited number of plants.
Insects that become severe on cabbage will probably also infect nearby mustard, broccoli, and collards. If an insect lays eggs, or otherwise attacks a specific species, the presence of unrelated plants in the area can interrupt progress of the attack by diluting the attractive odor of the preferred plants. This can also slow the spread of diseases and pests, giving the gardener more time to deal with them. Marigolds and garlic are two plants whose merits are frequently advocated as insect repellants, however, most of these claims have not been proven. In some cases the evidence indicates they are not effective.