Tebuconazole and azoxystrobin: understanding the fungicide potential of the combination used in a commercial formulation

• Autor(a) principal: Aguiar, Nuno Filipe Borges
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30950
• topic: Azoxystrobin; Tebuconazole; Custodia 320 SC; Fungicide; Plant protection products; Triazole; Strobilurin; Efficacy; Pyrenophora teres; Rhynchosporium secalis

Specific information towards each fungicidal active ingredient and its effects on all local organisms, whether they’re pathogens, non-target organisms or crops is still largely lacking. In this study, the potential effects of azoxystrobin, tebuconazole and a commercial formulation with these two active ingredients combined, known as Custodia 320 SC, were tested on two fungal species, Pyrenophora teres and Rhynchosporium secalis, both well known worldwide pathogens responsible for worldwide losses in important crops such as barley and rye. The results indicated significant resistance to both active ingredients by P. teres, with tebuconazole-treated cultures showing the lowest inhibition in the growth response. R. secalis showed also low and poorly variable growth inhibition rates for both fungicides, never reaching to 50% inhibition in comparison to the respective control. These results were obtained considering exposure concentration ranges within the limits of water solubility for both compounds and including concentrations that correspond to typical application rates used in the field to treat affected crops. Nevertheless, bacterial contamination in early trials allowed to observe that under these conditions the efficacy of the fungicides is superior (fungal growth inhibition rate over 50%) until a certain level of exposure, from which onwards the efficacy is again limited; this effect can be explained by a reduction of the fungi resistance capacity in competitive scenarios. The efficacy of the combined active ingredients was lower than equivalent treatments in trials where they were applied singly, suggesting the possibility of antagonistic interactions between azoxystrobin and tebuconazole. Additionally, the comparison of effects promoted by the combination of the active substances with their equivalent combinations applied via commercial formulation demonstrated that the formulants other than the active substances used in the commercial formulation do not promote their efficacy when the target organisms are P. teres or R. secalis.