THE POTENTIAL FOR COMMON WEEDS TO REDUCE SLUG DAMAGE TO WINTER-WHEAT - LABORATORY AND FIELD STUDIES

1. Slugs are serious pests of winter wheat crops in temperate climates , but current methods of chemical control are often unreliable. This p aper investigates the potential for common agricultural broad-leaved w eeds to act as an alternative food source for slugs, thereby reducing damage to the crop, as part of an integrated approach to pest slug man agement in wheat crops. 2. An experiment carried out in the field exam ined the relative effectiveness of metaldehyde pellets and three weed species in reducing damage to wheat seeds and seedlings. Treatments we re carried out in open-topped arenas, each containing eight adult fiel d slugs Deroceras reticulatum. The presence of weeds that were palatab le to slugs did limit damage to the crop but, over a 72-h period, meta ldehyde provided the most effective level of control. 3. A laboratory experiment was carried out to study the feeding behaviour of the slugs in more detail. A single slug was placed in an arena containing food items attached to electronic probes that could detect bites by a slug. The presence of dandelion Taraxacum officinale leaves, a palatable sp ecies, reduced the number of wheat seeds damaged, but chickweed Stella ria media leaves, which are less palatable to slugs, had no effect. Mo st slugs ate the first food item encountered. When dandelion was eaten first, significantly fewer wheat seeds were damaged, and slugs subseq uently took fewer bites on seeds than when either a seed or chickweed was eaten first. Slugs were more likely to ignore wheat seeds after a meal on dandelion. 4. Metaldehyde pellets tend to degrade a few days a fter application. It is suggested that weeds could provide an on-going degree of protection to the crop after the pellets have degraded and until the wheat plants have developed beyond the vulnerable stages. Ho wever, the importance of the palatability of the weeds to slugs, and a high weed density to ensure an early encounter with a weed plant duri ng a foraging session, are highlighted by the laboratory study.