Fusarium head blight (FHB), caused by Fusarium graminearum, significantly reduces yield, and leads to grain contamination with mycotoxins under warm, humid conditions during pre- and early post-anthesis periods. Thus, fungicides are most warranted for FHB control when wet, rainy conditions occur during and shortly after anthesis. Here, we investigated the influence of persistent post-anthesis rainfall on the efficacy of tebuconazole+prothioconazole (Prosaro) in combination with genetic resistance against FHB and mycotoxins in two field experiments conducted during 2018 and 2019 in Wooster, OH. Separate plots of susceptible (S), moderately susceptible (MS), and moderately resistant (MR) soft red winter wheat cultivars were treated at anthesis (TR) or left untreated (UT), inoculated with a spore suspension of Fusarium graminearum, and then subjected to one of three simulated rainfall regimes: R1) rain during the first 10 days after anthesis, R2) rain during the second 10 days after anthesis, and R3) no simulated rainfall. Relative to the susceptible UT check, mean FHB index (IND), deoxynivalenol (DON) and zearalenone (ZEA) contamination of grain were lowest, and mean grain yield (YLD) and test weight (TW) were highest under all rainfall regimes when the fungicide was applied to the MS or MR cultivar. The estimated net cash income (NCI) of integrated management (IM) programs was consistently higher than the NCI of fungicide-only or resistance-only programs across different grain prices and fungicide application costs under all rainfall regimes. Post-anthesis rainfall had a greater effect on the efficacy of TEBU+PROT against DON than IND. Mean DON was considerably higher in UT plots subjected to R1 (UT_R1) than R2 or R3 across all cultivars. However, DON levels were similar for R1 and R2 when plots received an anthesis application of Prosaro. Estimated slopes for relationships between IND and DON (on the log scale) were highest for UT_R1, but not significantly different among the three simulated rainfall regimes for TR, suggesting that the efficacy of Prosaro at reducing the rate of increase in mean DON per unit increase in mean IND was not compromised under R1. Under R2, estimated slopes were not significantly different between UT and TR. Persistent rainfall shortly after anthesis had little effect on the efficacy of Prosaro against DON, but efficacy was severely compromised by persistent late-season rainfall.

ACKNOWLEDGEMENTS AND DISCLAIMER: This material is based upon work supported by the U.S. Department of Agriculture, under Agreement Nº 59-0206-4-018. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.