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Control of downy mildew (Peronospora sparsa) in arctic bramble (Rubus arcticus ssp. arcticus)

Kostamo, K., Toljamo, A., Palonen, P., Valkonen, J.P.T., Kärenlampi, S.O., Kokko, H.
Annals of applied biology 2015 v.167 no.1 pp. 90-101
European Union, Peronospora, Rubus arcticus, Rubus plicatus, agrochemicals, blackberries, boysenberries, cultivars, downy mildew, elicitors, fruits, fungicides, leaves, pathogens, pesticide law, profitability, Arctic region, Finland
Downy mildew, inflicted by Peronospora sparsa, causes yield losses in arctic bramble (Rubus arcticus ssp. arcticus), boysenberry (Rubus spp. hybrid) and blackberry (Rubus fruticosus), and is a serious threat to the cultivation. Arctic bramble is a high‐value crop but its commercial potential is not realisable partly due to downy mildew. Although P. sparsa has been associated with yield losses in arctic bramble, this has not been experimentally proven, nor have the downy mildew symptoms in arctic bramble fruits been described in a controlled experiment. In this study, downy mildew was found to affect the fruits and reduce the yield of arctic bramble. There was a direct correlation between the number of infected leaves and hard fruits resulting from the infection. Owing to the new pesticide legislation in the European Union, it is important to find alternatives to fungicides in the control of downy mildew. The products ALIETTE (fungicide), PHOSFIK (leaf fertiliser) and BION (pathogen defence elicitor) were effective in downy mildew control, Aliette and Phosfik being more effective than Bion especially in preventing yield losses. No arctic bramble cultivars known to be resistant to downy mildew are available. Evaluation of cultivars Alli, Mesma and Pima in the field showed that Mesma is more resistant to downy mildew than are Alli and Pima. Currently the main cultivar grown in Finland, Pima, was the most susceptible variety. The results of this study suggest that the yields and profitability of arctic bramble production could be improved by selecting more resistant varieties, combined with the application of agrochemicals that can suppress the development of downy mildew.