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

Abstract

Eleven fungicides, benomyl, bitertanol, captan, carbendazim, mancozeb, procymidone, propiconazole, tebuconazole, thiram, triadimenol and tridemorph, were tested in vitro at 50 and 10 mg a.i./L for their effects on the macroconidial germination of Claviceps africana, the sorghum ergot pathogen. Thiram and captan completely inhibited conidial germination of the two isolates (UQE1 and UQE2) tested. Nine of the best fungicides from this test were selected for assessment as seed treatments using sorghum seed which had been artificially coated with ergot honeydew containing macroconidia of the isolates UQEl or UQE9. Captan and thiram at 0.5, 1 and 2 g a.i./kg seed completely inhibited macroconidium germination of one isolate and reduced germination of the other to <0.2%. Thiram applied to honeydew-coated sorghum seed completely inhibited macroconidium germination at a rate lower than that currently registered (2.4 g a.i./kg) for use on sorghum seed in Australia. These results have important implications for the movement of sorghum seed from areas where C. africana is endemic to areas which are free from the pathogen.