Quantitative Review of the Effects of Triazole and Benzimidazole Fungicides on Fusarium Head Blight and Wheat Yield in Brazil

Abstract

Triazole and benzimidazole fungicides have been used for controlling Fusarium head blight (FHB) in wheat for over two decades. In Brazil, it was only during the last five years that uniform fungicide trials for FHB control have been established yearly, thus contributing to a new large body of fungicide efficacy data for this country. A systematic review of both peer- and non-peer-reviewed studies on chemical control conducted since 2000 in Brazil was performed. Fungicides of interest were the triazoles tebuconazole (TEBU_1x and TEBU_2x) and propiconazole (PROP_2x), and the benzimidazole carbendazim (CARB_2x). Most fungicides were applied twice, the first at early to mid-flowering and the second 7 to 10 days later. Only TEBU was tested as one or two applications, and thus four treatments were evaluated. For these fungicides, there were 35 trials reporting FHB index and 48 reporting mean yield. Network meta-analytic models were fitted to the data of the log of the means of FHB index for each fungicide and for the nontreated check. The meta-analytic estimates were used to obtain control efficacy ( $\overline{C}$ ), or percent disease reduction relative to the nontreated check. The absolute mean difference ( $\overline{D}$ ) in yield (kg/ha) between the fungicide-treated and the nontreated check plots was also estimated. Yield response relative to the nontreated check ( $\overline{Y}$ ) was also calculated based on the difference in the logs of the means of yield between fungicide-treated and nontreated check. The TEBU_1x, TEBU_2x, and CARB_2x treatments performed similarly with regards to control efficacy (= 59%, 53% and 55%, respectively), and although better than PROP_2x (47%), the difference was marginally significant. Yield response ( $\overline{D}$ ) was highest for TEBU_2x, ( $\overline{D}$ = 558 kg/ha, $\overline{Y}$ = 19.2%) followed by PROP_2x (497 kg/ha, 16.0%), TEBU_1x (457 kg/ha, 17.3%), and CARB_2x (456 kg/ha, 12.8%). For an average 2016 scenario of fungicide plus application costs (F_C = $18 U.S./ha) and average wheat price (W_P = $215 U.S./MT), the probability of breaking even on the financial investment in the four treatments ranged from 59 to 63%. For 140 scenarios (four fungicides) created based on the combination of five W_P ($133 to 266 U.S./MT) and seven F_C ($5 to 35 U.S./ha), the probability of breaking even was >50% for all but two scenarios. The information may serve as a guide for planning future trials and provides a baseline and first step toward optimizing FHB management in Brazil.