Laboratory and field evaluation of fungicides for the management of sugarcane smut caused by Sporisorium scitamineum in seedcane

Sugarcane smut caused by Sporisorium scitamineum is one of the most devastating diseases of sugarcane. Two trialzole fungicides, propiconazole and triadimefon, have been used to protect seedcane from infection with sugarcane smut elsewhere, particularly after hot water treatment. These fungicides were registered under an emergency permit in Australia when smut was found for the first time in Queensland in 2006. A research program was initiated to screen and evaluate a range of fungicides against sugarcane smut. Nine fungicides were tested in vitro at various concentrations for their efficacy on smut spore germination. Azoxystrobin (Amistar®), quintozene (Quintozene® 750) and didecyl dimethyl ammonium chloride (Steri-max®) completely stopped germination of teliospores at 2.5 mg a.i./L. Propiconazole (Tilt®), triadimefon (Bayleton®), cyproconazole (Alto®) and acibenzolar-s-methyl (Bion®) significantly (P < 0.05) reduced spore germination at 50, 100 and 200 mg a.i./L. Two field trials were planted in spring 2008 and autumn 2009, where cane setts that had been inoculated with smut were dipped in a range of fungicide suspensions for five or 10 min, prior to planting. Cyproconazole, propiconazole, triadimefon and azoxystrobin significantly (P < 0.05) suppressed disease expression for up to 6 months in a summer experiment and 9 months in an autumn experiment. These results have important implication for selecting new fungicides for the control of sugarcane smut in seedcane that is provided to Australian sugarcane growers as a disease-free propagation source.