The benefits of unsprayed cereal crop margins to grey partridges Perdix perdix and pheasants Phasianus colchicus in Sweden

Unsprayed cereal crop margins were tested in large-scale field trials durin g 1991-1994, as part of the Swedish agricultural authorities' nation-wide c ampaign to reduce pesticide usage. Eleven pairs of farms in central and sou thern Sweden were chosen. One farm in each pair was sprayed normally (i.e. 90-100% of cereal fields were treated annually with herbicides; insecticide s and fungicides were only used after pest and disease thresholds had been exceeded), whilst on the other farm the outer six metres of crop of several cereal fields received no pesticides. In each year, unsprayed crop margins in both autumn- and spring-sown cereals had significantly higher percentag es of weed cover. Unsprayed crop margins supported higher densities of nont arget arthropods, particularly the non-pest species which are important in the diet of insect-eating gamebird chicks. Significant positive relationshi ps were observed between the densities of these insects and the degree of w eed cover. Mean brood sizes and chick survival rates of both grey partridge s Perdix perdix and pheasants Phasianus colchicus were higher on farms with unsprayed crop margins. The effects of omitting herbicide (pesticide) trea tments were most dramatic for grey partridges. The treatment, both by itsel f and mediated through insect density and weed cover, had highly significan t effects on brood sizes. There was a significant increase in the mean numb er of pairs of partridges found in spring on farms with unsprayed cereal cr op margins. No similar increase was observed for pheasants. The benefits of unsprayed cereal crop margins to partridges and pheasants are discussed.