Fungicide treatment of sunflower seed to inhibit germination of admixed sclerotia of Sclerotinia sclerotiorum

Abstract

Sunflower seed lots infected with sclerotia of Sclerotinia sclerotiorum provide a means of dispersal of the fungus. To find a chemical control, sclerotia were dusted or dipped with 19 chemical formulations. Eight of these (benomyl 50%, benomyl 15% plus lindane 1%, thiabendazole wettable powder, thiabendazole 45% water-based flowable, iprodione 50%, dithianon 75%, omadine 50% and thiophanatemethyl 70%) completely inhibited germination of sclerotia when in direct contact with and covering the organism. Sclerotia were able to germinate if these chemicals were removed by washing, but germination was significantly lower for those sclerotia which had been treated with benomyl 50%, benomyl 15% plus lindane 1% (Bennel 13, thiabendazole 90% and 45%, iprodione 50% and thiophanate-methyl 70% than for dithianon 75% and omadine 50%. When sclerotia were buried in moist soil for 1 month those treated with formulations of benomyl, thiabendazole and iprodione did not germinate on potato dextrose agar, while the germination percentages of those treated with dithianon, ornadine and thiophanate-methyl were not significantly different from that for germination of sclerotia which had not been treated. When thiabendazole, benomyl and iprodione were used at 3 rates to treat sunflower seed infested with sclerotia, thiabendazole was the most effective fungicide in preventing germination of sclerotia. This result was confirmed when the fungicide was used commercially to treat lots of sunflower seed containing sclerotia. As thiabendazole had no apparent effect on gerrnination of sunflower seed it could be used to treat sunflower seed containing low levels of sclerotia to prevent previously uninfested areas being contaminated with S. sclerotlorum during sowing operations.