Potato crops should be sampled before lifting in order to assess the level of tuber blight and soft rot potential, the Central Science Laboratory has advised.

The combination of both diseases – as in many crops affected by wet weather this summer – could have a much higher impact than either disease alone, even in well managed stores, it said.

That was because infection of tubers by the blight fungus created a microclimate suitable for the entry and multiplication of soft rot bacteria, leading to ‘hot spots’ within the stored crop.

CSL’s John Elphinstone said the best way to assess the risk was to sample and wash 300 tubers from the field, incubate them in a “hot box” at 18-25C and observe disease development over one week. Samples could alternatively be sent to a laboratory for analysis.

“Once test results are known, potato crops can be graded in terms of storage risk. High risk areas of fields, for example from waterlogged spots or tramlines, can also be identified and stored separately or sent straight to market or processing.”

At-risk crops should be dried and cooled as quickly as possible and monitored closely.