Sampling, extraction and incidence of redberry mites (Acalitus essigi) on blackberries in Australia

‘Redberry disease’ on blackberries is hypothesised to be caused by the redberry mite (RBM), Acalitus essigi (Hassan), and results in uneven ripening of blackberry drupelets, which become bright red, hard and inedible. This damage has been reported to cause significant crop losses in commercial blackberry production in most regions where commercial blackberries are grown. However, RBM are difficult to detect and manage due to their tiny body size. In this study, a new ‘shake and wash’ extraction method has been developed, enabling faster, more accurate mite detection and quantification. The ‘shake and wash’ method extracted significantly more RBM and predatory mites (Phytoseiidae) than the previously recommended ‘sticky tape’ method, where mite extraction using this technique was increased by 53 and 60%, respectively. RBM counts were then made from the fruit of wild and commercial blackberry cultivars. Significantly higher RBM populations were isolated in cultivars ‘BL454’ (mean = 12.1 per fruit) and ‘Chester’ (mean = 2.6 per fruit) from several sites indicating potential RBM susceptibility in these cultivars. The highest levels of disease incidence and RBM numbers were observed on wild blackberry fruit. The redberry disease incidence increased from 13.5 to 44.9% as the mean population of RBM increased on wild fruit. Further methods were developed to extract mites from winter buds on canes. RBM numbers were lower in the fruit compared to winter buds. RBM detection is best achieved in winter buds rather than fruit and may be an important tool for RBM detection and subsequent management in the cropping season.