However, the presence of the microscopic blackberry (or red berry) mite appears to be neither necessary nor sufficient precondition.
EMR researchers, funded by the Horticultural Development Company, found the mites were particularly prevalent in the Chester variety, yet absent on Loch Ness. A range of acaricide treatments was trialled and compared to untreated plants.
"All significantly reduced mite populations," said Harris. They all reduced emergence of red berry by a similar level, he said, although the contrast with untreated plants was not as marked.
"There appears to be some other cause not affected by the acaricides," said Harris, but he suggested that the vegetable-derived Codacide oil had fewer drawbacks than other treatments.