Responses of slug numbers and slug damage to crops in a silvoarable agroforestry landscape.
Abstract
Alternative farming practices such as set-aside and agroforestry are likely to be of continuing interest to European agriculture but may have associated problems, such as increased populations of crop pests such as slugs. A silvoarable agroforestry experiment has been in progress since 1987 at Leeds University Farms at Bramham, West Yorkshire, UK. It consists of four replicate blocks, each with rows of trees separating alleys of arable crops; all four blocks have their own arable control areas in adjacent fields. Pitfall trap catches within the experiment indicate that the slug population increased over the period 1991-94. The increase was greatest, and most consistent, within the tree rows in the agroforestry blocks. The increase was slower and less consistent in the arable controls and the arable areas within the agroforestry blocks. In spring 1994, the slugs in each of the treatments in the agroforestry experimental area were sampled using pipe traps, refuge traps and pitfall traps. The number and diversity of slugs were highest in the grassed understorey beneath the rows of trees and significantly higher in the alleys between the rows of trees than in the arable control areas. The levels of slug damage to a pea crop were assessed by surveys that recorded the number of emerging plants and the number of damaged leaves per plant. There were significant correlations between the number of slugs caught and the damage to the crop by slugs. It is concluded that slugs have the potential to be important pests of some crops in silvoarable agroforestry landscapes and that this could influence the choice of crops for this type of farming.