Insects see crops clearly when the weeds have gone

All gardeners know that their plants have to compete against insects and weeds. We apply insecticides to protect plants from the munching hordes, and we apply herbicides, or hoe, to protect plants from weeds. But, according to Stan Finch and Rosemary Collier of Horticulture Research International, Wellesbourne, the latter is a bad move that actually helps insects to find our crop plants.

Writing in the June issue of Biologist, Finch and Collier provide evidence that specialist insects, those that feed on specific plant species, can be prevented from finding their host plants if other plants are grown alongside. The type of decoy plant is irrelevant, since green cardboard models also do the trick. It seems that insects fly onto and off of a plant several times to check its suitability for egg-laying. A plant surrounded by bare soil is therefore likely to be found by an insect more times than one surrounded by other green plants, and insects are more successful in a carefully weeded crop field than in one containing weeds. Since insecticides kill only a fixed percentage of insects, more insecticides may have to be applied to a weeded crop to maintain the current level of pest control. The solution? Cultivate your weeds!