VARIATION IN THE OCCURRENCE OF RUST (MELAMPSORA SPP) AND OTHER DISEASES AND PESTS, IN SHORT-ROTATION COPPICE PLANTATIONS OF SALIX IN THE BRITISH-ISLES

A proportional odds model was employed to analyse simple assessments o f disease and pest severity in plantings of short-relation coppice wil lows at 18 sites in the UK over a 5-year period (1987-1991). Of a wide range of fungal diseases and pests encountered, the most severe and d amaging were rusts, caused by Melampsora spp., and feeding damage due to beetles of the family Chrysomelidae. For rust, the model revealed h ighly significant (P <0.001) interactions between the main factors, di sease development within a season and between seasons, clones and site s. Within seasons, rust severity increased more at sites in the northe rn than in the southern UK, due mainly to low levels of occurrence at the northern sites early in the season. There was a gradual increase i n rust severity over the 5-year period, although clones differed both in terms of disease severity and the extent of change in severity in a ny one year. Beetle feeding damage was also analysed in a similar way, indicating a general increase from 1987-1989, but also revealing diff erential patterns over time and between sites.