Trap Ditches

ditches for catching plant pests, such as the beet pest Bothynoderes punctiventris and the caterpillars of turnip moths, gamma moths, and beet webworms, which crawl from contaminated areas and from wintering and reproduction sites. The insects that are trapped in the ditches are exterminated by mechanical means or insecticides. The ditches are tapered toward the top. The center depth is 13–15 cm, and the width along the top is 6–7 cm. The depth of the sides is 30 cm, and the bottom width is 13–15 cm. Wells are bored 5–10 m apart from one another along the entire length of the bottom of the ditch. Trap ditches are dug in nurseries to separate young crops from the woods and fresh cuttings and to limit the spread of caterpillars beyond an enclosed planting area. They are also a means of observing the appearance of new species of pests.