A commercially acceptable assessment technique for improved control of cabbage stem flea beetle feeding on winter oilseed rape

Highly significant relationships between the percentage of leaves showing P sylliodes chrysocephala (L.) feeding scars and the mean number of larvae pe r plant during autumn, were established from 457 fields (over five differen t years) in England and Wales, and used to define an index of leaf scarring as an alternative assessment method for control decisions. The index was t ested in conjunction with autumn samples using datasets from 786 fields (si x years). An action threshold of 50% leaves scarred resulted in similar tre atment advice to the current plant dissection method in over 98% of cases. During spring, the relationship between percentage leaves scarred and mean number of larvae per plant was not consistent between years and the index c annot be used for population assessment at this time of year. (C) 2001 Else vier Science Ltd. All rights reserved.