In vitro screening and evaluation of fungicides for the control of Claviceps africana on sorghum seed

Eleven fungicides, benomyl, bitertanol, captan, carbendazim, mancozeb, proc ymidone, propiconazole, tebuconazole, thiram. triadimenol and tridemorph, w ere tested in vitro at 50 and 10 mg a.i./L for their effects on the macroco nidial germination of Claviceps africana, the sorghum ergot pathogen. Thira m and captan completely inhibited conidial germination of the two isolates (UQE1 and UQE2) tested. Nine of the best fungicides from this test were sel ected for assessment as seed treatments using sorghum seed which had been a rtificially coated with ergot honeydew containing macroconidia of the isola tes UQE1 or UQE9. Captan and thiram at 0.5, 1 and 2 g a.i./kg seed complete ly inhibited macroconidium germination of-one isolate and reduced germinati on of the other to <0.2%. Thiram applied to honeydew-coated sorghum seed co mpletely inhibited macroconidium germination at a rate lower than that curr ently registered (2.4 g a.i./kg) for use on sorghum seed in Australia. Thes e results have important implications for the movement of sorghum seed from areas where C. africana is endemic to areas which are Free from the pathog en.