EPA Issues Label Approving Mertect in Sweetpotatoes

— Written By and last updated by Mary Lorscheider
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Updates for Sweetpotato Producers in NC: EPA issues Section 3 label for Mertect (thiabendazole) in sweetpotatoes postharvest and EU raises MRL to 3 ppm

From Dr. Lina Quesada-Ocampo and Camilo H. Parada-Rojas

Sweetpotatoes remain an important commodity for North Carolina. However, postharvest diseases can result in significant crop losses, especially in exports due to shipping times and conditions. Sweetpotato black rot, caused by the fungal pathogen Ceratocystis fimbriata, is one disease that can cause damage in sweetpotatoes postharvest and requires integrated strategies, including application of fungicides, for management.

black rot symptoms on Sweetpotato

Dark, dry lesions on a sweetpotato are a typical symptom of black rot caused by Ceratocystis fimbriata.

Recently, the United States Environmental Protection Agency (EPA) issued a Section 3 label for the fungicide Mertect (thiabendazole) to be used in sweetpotatoes postharvest for control of black rot. This fungicide has also shown
efficacy against other sweetpotato postharvest diseases of economic importance. This means that Mertect is no longer under a Section 18 emergency label only available in North Carolina for postharvest use in sweetpotatoes and can now be used under the Section 3 label in the entire US.

For producers and packers that seek to export sweetpotatoes to the European Union, the European Commission revised the Maximum Residue Level (MRL) allowed for thiabendazole (Mertect) in imported sweetpotatoes and increased it from 0.01 ppm to 3 ppm. With this MRL update producers and packers now have another tool at their disposal for integrated management of devastating fungal pathogens when exporting sweetpotatoes to European markets.

If you think you may have sweetpotato black rot in your roots and need assistance with diagnostics or management, please contact your local Extension agent and send physical samples and/or photos to the Plant Disease and Insect Clinic. For additional management options, please refer to those listed in our disease factsheet.