The potential for common weeds to reduce slug damage to winter wheat: laboratory and field studies.
Slugs are serious pests of winter wheat crops in temperate climates, but current methods of chemical control are often unreliable. The potential for common agricultural broad-leaved weeds to act as an alternative food source for slugs was studied, thereby reducing damage to the crop, as part of an integrated approach to pest slug management in wheat. An experiment carried out in the field in the UK examined the relative effectiveness of metaldehyde pellets and three weed species in reducing damage to wheat seeds and seedlings. Treatments were carried out in open-topped arenas, each containing eight adult field slugs (Deroceras reticulatum). The presence of weeds that were palatable to slugs did limit damage to the crop, but over a 72-h period, metaldehyde provided the most effective level of control. 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. The presence of Taraxacum officinale leaves, a palatable species, reduced the number of wheat seeds damaged, but Stellaria media leaves, which are less palatable to slugs, had no effect. Most slugs ate the first food item encountered. When T. officinale was eaten first, significantly fewer wheat seeds were damaged, and slugs subsequently took fewer bites on seeds than when either a seed or S. media was eaten first. Slugs were more likely to ignore wheat seeds after a meal on T. officinale. Metaldehyde pellets tended to degrade a few days after application. It was suggested that weeds could provide an on-going degree of protection to the crop after the pellets had degraded, and until the wheat plants had developed beyond the vulnerable stages. However, the importance of the palatability of the weeds to slugs, and a high weed density to ensure an early encounter with a weed plant during a foraging session, are highlighted by the laboratory study.