Verticillium survey results: Is it in red raspberry production fields?

Authors: Weiland, Gerald - Jerry

Submitted to: Washington Small Fruit Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/6/2017
Publication Date: 1/10/2017
Citation: Weiland, G.E. 2017. Verticillium survey results: Is it in red raspberry production fields?. Washington Small Fruit Conference. Whatcom Ag Monthly. 5(12).

Interpretive Summary: In 2012, Verticillium wilt was diagnosed in several grower fields where it was causing raspberry plants to wilt and die in late summer. Similar symptoms were seen in many other grower fields, so there was concern that Verticillium wilt might be a widespread problem in the industry. To determine whether Verticillium or other pathogens were responsible for the disease in grower fields, we searched for soilborne pathogens at 71 field sites. We found that Verticillium was frequently found in the soil, but was rarely isolated from sick plants. Nematodes were also commonly encountered, but were not associated with disease. However, Phytophthora, the cause of root rot, was frequently isolated from sick plants and was commonly found in the soil around diseased plants. These results are important because they show growers that Phytophthora, not Verticillium, is the main cause of diseased plants in late summer. Therefore, growers should use disease control options for Phytophthora, not Verticillium.

Technical Abstract: Preliminary results of the survey for Verticillium dahliae, the cause of Verticillium wilt, in the Washington Red Raspberry industry were reported at the 2016 Washington Small Fruit Conference. Verticillium was found in many field soils, but was rarely isolated from plants and was just as likely to occur at healthy sites (no diseased plants) as from disease sites (with diseased plants). Two detection methods were used and the DNA-based method was better at detecting Verticillium than the culture-based method. Root lesion nematodes were also assessed, but population numbers in healthy sites were similar to those in disease sites. However, Phytophthora rubi, the cause of Phytophthora root rot, was more likely to occur at disease sites than healthy sites and was much more likely to be isolated from diseased plants. Based on these results, Phytophthora root rot is a more widespread problem than Verticillium wilt.