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POSTERS: Analytical and theoretical plant pathology

Post-anthesis Rainfall effects on the Efficacy of Tebuconazole+Prothioconazole against Fusarium head blight and Deoxynivalenol in wheat
Wanderson Bucker Moraes - The Ohio State University. Pierce Paul- The Ohio State University, Laurence Madden- The Ohio State University

The influence of persistent post-anthesis rainfall on the efficacy of tebuconazole+prothioconazole (TEBU+PROT) against Fusarium head blight (FHB) and deoxynivalenol (DON) was investigated. Separate plots of susceptible (S), moderately susceptible (MS), and moderately resistant (MR) cultivars were treated at anthesis (TR) or left untreated (CK), 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 rainfall. FHB index (IND) and DON were quantified, and efficacy was estimated as percent control (C) of both responses relative to CK under each rainfall regime. Relative to the susceptible CK (S_CK), C for both IND and DON was highest under all rainfall regimes when the fungicide was applied to the MS or MR cultivar (MS_TR and MR_TR). Post-anthesis rainfall had a greater effect on efficacy against DON than against IND, with considerably lower C values for R2 than R1 and R3. For instance, relative to S_CK, C for DON with MR_TR was 74% for R3, 68% for R1, and only 42% for R2. Similarly, within a given resistance class, C for DON was comparable between R1 and R3 (57-61%), but much lower for R2 (23-42%). Persistent rainfall shortly after anthesis had little effect on the efficacy of TEBU+PROT against IND and DON, but efficacy against DON was severely compromised by persistent late-season rainfall.