EFFECTS OF POPULATIONS OF THE EUROPEAN RED MITE, PANONYCHUS ULMI, ON THE APPLE VARIETY RED DELICIOUS IN NOVA SCOTIA

The effects of Panonychus ulmi (Koch) density on several yield components of Red Delicious apples in a Nova Scotia orchard were examined from 1967 to 1970. The same 96 trees were sampled in each of the 4 years, and from a peripheral sampling zone within each tree the number of dormant and blossom clusters and the eventual number of apples produced was determined. The other yield components — bloom, set, and crop — were computed from these counts. Applications of ryania, carbaryl, and animert on 6 June 1967 followed by supplementary applications of animert on 7 July (carbaryl plots) and 1 August (ryania plots) were used to induce varying densities of P. ulmi . Mites were sampled twice weekly from June to August and fortnightly in September. Chemical treatments in 1967 had significant effects on mite-days/leaf in each year from 1967 to 1970. Cumulative mite-days/leaf had a significant negative influence on the number of harvested apples/sampling zone in 1967 and 1969, the years of higher apple production and higher mean bloom, but not in 1968 and 1970. Mites in 1969 also had a significant negative effect on return bloom in 1970. These findings agree with other studies that suggest an interaction between fruit load and yield losses induced by mites.