Incidence and control of black spot syndrome of tiger nut

Tiger nut (Cyperus esculentum) is a very profitable crop in Valencia, Spain, but in the last years, part of the harvested tubers presents black spots in the skin making them unmarketable. Surveys performed in two consecutive years showed that about 10% of the tubers were severely affected by the black spot syndrome whose aetiology is unknown. Disease control procedures based on selection of tubers used as seed (seed tubers) or treatment with hot‐water and/or chemicals were assayed in greenhouse. These assays showed that that this syndrome had a negative impact on the germination rate, tuber size and yield. Selection of asymptomatic seed tubers reduced drastically the incidence of the black spot syndrome with respect to using seed tubers with severe symptoms (selection of healthy seed tubers was not possible because the causal agent is undetermined). Thermal treatment of seed tubers with severe symptoms reduced the number of unmarketable harvested tubers by half but was detrimental for the germination. Chemical treatments of seed tubers with severe symptoms decreased the incidence of the black spot syndrome about 40% for sodium hypochlorite and about 10% for hydrochloric acid, trisodium phosphate and the fungicide trioxystrobin.