AVALIAÇÃO DA SENSIBILIDADE DE Exserohilum turcicum A FUNGICIDAS SISTÊMICOS

Abstract

Intensive and criteria-free use of systemic fungicides to combat disease in maize can select resistant pathogen populations, making control more difficult and increasing crop losses. Among these pathogens may be the fungus Exserohilum turcicum, a causative agent of helminthsporiosis, a disease that causes a reduction in green leaf area index. Therefore, the aim was to evaluate the sensitivity of the causative agent of helminthsporiosis to the systemic fungicides tebuconazole, trifloxystrobin + tebuconazole and azoxystrobin + benzovindiflupir. Six isolates of the pathogen were obtained from symptomatic maize plants in the Maringá region, and then, bioassays were performed to evaluate the sensitivity of Exserohilum turcicum mycelial growth to the selected fungicides at concentrations of 1, 10, 50 and 100 ppm more the witness. The experimental design adopted was completely randomized with 4 replications. To quantify mycelial growth, perpendicular measurements of fungal colonies were made in each treatment. Data were subjected to regression analysis to obtain the ED50. The active ingredient trifloxystrobin + tebuconazole was highly fungitoxic for half of the isolates and the remaining moderately fungitoxic, in which case the isolates were classified as high and medium sensitivity, respectively. For the fungicide tebuconazole, two of the isolates showed high sensitivity and the rest were moderately sensitive. An insensitive isolate was detected with azoxystrobin + benzovindiflupir mixture and the others showed high and medium sensitivity to the product. It was concluded that among the evaluated fungicides only the azoxystrobin + benzovindiflupir mixture presented a product insensitive isolate, that is, resistant to it.