Are DMI+QoI premixes applied during flowering worth for protecting wheat yields from Fusarium head blight? A meta-analysis

Fusarium head blight (FHB), caused mainly by Fusarium graminearum, is best controlled with demethylation inhibitor (DMI) fungicides applied during flowering. However, the use of premixes of DMI and quinone outside inhibitor (QoI) fungicides to control FHB has increased in Brazil, but the individual results are inconsistent. Data on FHB severity and wheat yields measured in field experiments conducted in Brazil were gathered from both peer- and non-peer-reviewed sources published from 2000 to 2018. After applying selection criteria, 35 bibliographic sources, contributing 73 (50% from cooperative trials) trials, were identified. At least one of four DMI+QoI premixes and one tebuconazole (TEB) treatment, applied mostly twice (full-flowering and 10 days) tested in at least 14 trials and three year each, were present in a selected trial. Estimates of percent control (and respective 95%CI) by a network model ranged from 44.1% (pyraclostrobin + metconazole applied once; 32.4 - 53.7) to 64.3% (pyraclostrobin + metconazole; 58.4 - 69.3); the latter not differing from TEB (59.9%, 53.6 - 65.3). Yield response was statistically similar for pyraclostrobin + metconazole (532.1 kg/ha, 441 - 623) and trifloxystrobin + prothioconazole (494.9 kg/ha, 385 - 551), and both differed statistically from a group composed of TEB (448.2 kg/ha, 342 - 554), trifloxystrobin + TEB (468.2 kg/ha, 385 - 551), azoxystrobin + TEB (462.4 kg/ha, 366 - 558) and pyraclostrobin + metconazole applied once (413.7 kg/ha, 308 - 518). The two categories of FHB index (7% cut off) and yield (3,000 kg/ha), both in the non-treated check, did not explain the heterogeneity in the estimates. The probability of not-offsetting control costs was generally lower than 0.45 for scenarios considering two sequential sprays of the low-cost TEB or one spray of pyraclostrobin + metconazole as management choices. The envisioned enhanced economic return, solely based on yield response, from using two sprays of DMI+QoI premixes to control FHB should be seen with caution given the marginal levels of profitability.