No. 11 — June 3, 2019

Norton and Mancozeb Phytotoxicity

In September of 2018, Lucie Morton and I, as well as other colleagues, had an email discussion about Norton and mancozeb phytotoxicity. Fact or fallacy? At the time, a grower in Virginia had reported that older Norton leaves would turn a distinctive tan or light brown on the underside of the leaves after being treated with mancozeb. These older basal leaves after about 30 days would get necrotic edges, curl and fall from the shoot.

From this initial conversation, we also learned that mancozeb is a profungicide. When mancozeb comes in contact with water ethylene bisisothiocynate sulfide (EBIS) is released. Further when EBIS is exposed to UV light ethylene bisisothiocynate (EBI) is formed. If these compounds find there way into the plant tissue then phytotoxicity is likely to occur.

This week, a grower in Missouri reported similar phytotoxicity symptoms on Norton after applying mancozeb.

I would like to know if other Norton growers have observed any phytotoxicity on Norton after applying mancozeb. Please contact me if you have observed phytotoxicity after applying mancozeb and please document the “phyto” with pictures.

D. S. Volenberg

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