Soil-borne diseases increasing in Finnish strawberry production

In Finland, strawberries are produced mainly in the open field, but production in tunnels is also increasing. Import of planting material has increased since 1995, and now most of the plants originate from nurseries in other EU-countries. In 2016-2019, young plants showing disease symptoms and older plants from poorly developed fields were collected in the main strawberry production area, Suonenjoki, in eastern Finland, and investigated for strawberry pathogens. Phytophthora cactorum, the causal agent of strawberry crown rot, was the most common pathogen detected. Strawberry crown rot is the most severe disease in the open field production. It causes plant losses due to the use of susceptible cultivars like 'Polka', which is the main cultivar still grown in the open field in Finland. The presence of Phytophthora fragariae, the causal agent of red core, in field soils was tested with a modified baiting test and molecular methods. Red core was first detected in 2012, and since then P. fragariae has been detected from soil samples with the methods applied in this study. P. fragariae causes severe plant losses in perennial open field production when precipitation is high in the autumn, and soils remain wet for a long period. Neopestalotiopsis clavispora was detected for the first time in 2016. It was isolated from crowns of recently planted and older plants showing reddish-brown discolouration, often together with P. cactorum or Fusarium oxysporum. Verticillium infections in strawberry fields were first detected in 2016 when V. dahliae was isolated from young plants. The pathogen was detected on susceptible cultivars 'Honeoye' and 'Sonata'.