Rainfastness of Prothioconazole + Tebuconazole for Fusarium Head Blight and Deoxynivalenol Management in Soft Red Winter Wheat

Efficacy of Genetic Resistance and Fungicide Application Against Fusarium Head Blight and Mycotoxins in Wheat Under Persistent Pre- and Postanthesis Moisture

Field experiments were conducted to investigate the efficacy of fungicide treatments in combination with genetic resistance against Fusarium head blight (FHB) and its associated mycotoxins under persistently wet pre- and postanthesis conditions in plots inoculated with Fusarium graminearum-colonized corn spawn. Treatments consisted of a single application of prothioconazole + tebuconazole at early anthesis (PA), or at 3 (P3), 6 (P6), or 9 (P9) days after early anthesis, or PA followed by a single application of metconazole at 3 (PA+C3), 6 (PA+C6), or 9 (PA+C9) days after early anthesis. PA and P3 were the most efficacious of the single-application treatments in terms of mean percentage control of FHB index (IND), deoxynivalenol (DON), zearalenone (ZEA), and mean increase in grain yield and test weight (TW) relative to the nontreated susceptible check (S_CK). The double-application treatments (PA+C3, PA+C6, and PA+C9) were the most effective of all tested fungicide programs. However, relative to S_CK, the highest overall mean percentage reduction in IND, DON, and ZEA and increase in grain yield and TW were observed when the double-application fungicide programs were integrated with genetic resistance. The estimated net cash income (NCI) of the integrated management (IM) programs was consistently higher than the NCI of other tested programs across different grain prices and fungicide application costs. Thus, the benefits of the two-treatment IM programs under highly favorable conditions for FHB development were enough to offset the cost of two applications, making these programs profitable.

Effects of cultivar resistances and chemical seed treatments on fusarium head blight and bread wheat yield-related parameters under field condition in southern Ethiopia

Fusarium head blight (Fusarium graminearum Schwabe), FHB, is considered among the economically significant and destructive diseases of wheat. Thus, the study was worked out at seven sites in southern Ethiopia during the 2019 main cropping year to decide the effects of host resistance and chemical seed treatment on the progress of FHB epidemics and to decide grain yield benefit and yield losses derived from the use of wheat cultivars integrated with chemical seed treatments. The field study was worked out with the integration of two wheat cultivars, including Shorima as well as Hidase, and five chemical seed treatments, including Carboxin, Thiram + Carbofuran, Imidalm, Proceed Plus, and Thiram Granuflo. Twelve experimental treatments were arrayed in factorial arrangement with randomized complete block design. Each experimental treatment was replicated three times and delegated at random to experimental plots within a block. Significant (P < 0.01) variations were observed among the evaluated treatment combinations for rates of disease progress, incidence, severity, the area under the disease progress curve (AUDPC), and yield-related parameters across the locations. Results showed that the lowest incidence was registered on Shorima treated with Thiram + Carbofuran fungicide (27.40%). The lowest mean disease severity was recorded from Shorima integrated with Imidalm (21.23%) and Shorima treated with Thiram + Carbofuran (21.78%). The AUDPC was as low as 211.27, 226.39, and 236.46%-days were recorded on Shorima treated with Imidalm, Thiram + Carbofuran, and Proceed Plus, respectively. The highest disease severity of 57.91% (Hidase) and 27.22% (Shorima), and AUDPC of 552.71%-days (Hidase) and 313.04%-days (Shorima) were recorded from untreated control plots of the two cultivars. Paramount grain yield was found from Shorima treated with Imidalm and Dynamic fungicides, each of which was noted with GY of 4.40 and 4.05 t ha⁻¹, respectively. Results also showed the highest yield losses (21.89 and 23.23%) were computed on untreated control plots of the cultivars Hidase and Shorima, respectively, compared with maximum protected experimental treatment for both cultivars. Moreover, cost-benefit analysis confirmed that Shorima treated with Imidalm exhibited the most prominent net benefit (NB) ($67,381.26 ha⁻¹) and benefit-cost ratio (BCR) (4.43), followed by Shorima treated with Thiram + Carbofuran (NB of $60,837.76 ha⁻¹ and BCR of 3.98). Based on the lowest yield loss and highest economic advantage, the use of Shorima treated with either Imidalm or Thiram + Carbofuran could be suggested to the farmers in the study areas and elsewhere having analogous agro-ecological conditions to manage the disease. However, sole use of chemical seed treatment is not as effective as post-anthesis aerial application up to maturity of the crop. For this reason, post-anthesis aerial application should be considered besides chemical seed treatment for effective management of FHB.

Assessing the Curative and Protective Impacts of Select Fungicides for Control of Powdery Mildew of Wheat

Powdery mildew, caused by the obligate fungal pathogen Blumeria graminis, has been increasing in incidence and severity on wheat in the Chesapeake Bay region of the mid-Atlantic United States. Although fungicides are used for in-season management of powdery mildew, no studies to date have assessed the ability of these products to control disease after pathogen arrival/infection (curative activity) and the duration of disease control provided after fungicide application (protective activity) under controlled conditions. Five commercially available fungicide products, including Caramba, Stratego YLD, Priaxor, Prosaro, and Trivapro, were applied at either 3 or 5 days after inoculation with B. graminis spores to assess curative activity. In a separate study, protective activity for these fungicides was assessed by applying fungicides and inoculating with B. graminis spores the same day and 21 and 42 days after fungicide application. All fungicides reduced powdery mildew severity on foliage compared with nontreated controls. Priaxor provided 11 to 18% less activity than other fungicides when applied curatively. All products provided protective control up to 42 days after inoculation, with Stratego YLD and Priaxor providing the greatest level of control at 68 and 56%, respectively. Our data indicate that different fungicides can have subtle differences in overall efficacy profiles that may translate to improved control or an extended control window in some situations, but all tested products provide very good to excellent control of powdery mildew on wheat.

Integrated Effects of Genetic Resistance and Prothioconazole + Tebuconazole Application Timing on Fusarium Head Blight in Wheat

Integrated Fusarium head blight (FHB) management programs consisting of different combinations of cultivar resistance class and an application of the fungicide prothioconazole + tebuconazole at or after 50% early anthesis were evaluated for efficacy against FHB incidence (INC; percentage of diseased spikes), index (IND; percentage of diseased spikelets per spike), Fusarium damaged kernel (FDK), deoxynivalenol (DON) toxin contamination, grain yield, and test weight (TW) in inoculated field trials conducted in 11 U.S. states in 2014 and 2015. Mean log response ratios and corresponding percent control values for INC, IND, FDK, and DON, and mean differences in yield and TW relative to a nontreated, inoculated susceptible check (S_CK), were estimated through network meta-analyses as measures of efficacy. Results from the analyses were then used to estimate the economic benefit of each management program for a range of grain prices and fungicide applications costs. Management programs consisting of a moderately resistant (MR) cultivar treated with the fungicide were the most efficacious, reducing INC by 60 to 69%, IND by 71 to 76%, FDK by 66 to 72%, and DON by 60 to 64% relative to S_CK, compared with 56 to 62% for INC, 68 to 72% for IND, 66 to 68% for FDK, and 58 to 61% for DON for programs with a moderately susceptible (MS) cultivar. The least efficacious programs were those with a fungicide application to a susceptible (S) cultivar, with less than a 45% reduction of INC, IND, FDK, or DON. All programs were more efficacious under conditions favorable for FHB compared with less favorable conditions, with applications made at 50% early anthesis being of comparable efficacy to those made 2 to 7 days later. Programs with an MS cultivar resulted in the highest mean yield increases relative to S_CK (541 to 753 kg/ha), followed by programs with an S cultivar (386 to 498 kg/ha) and programs with an MR cultivar (250 to 337 kg/ha). Integrated management programs with an MS or MR cultivar treated with the fungicide at or after 50% early anthesis were the most likely to result in a 50 or 75% control of IND, FDK, or DON in a future trial. At a fixed fungicide application cost, these programs were $4 to $319/MT more economically beneficial than corresponding fungicide-only programs, depending on the cultivar and grain price. These findings demonstrate the benefits of combining genetic resistance with a prothioconazole + tebuconazole treatment to manage FHB, even if that treatment is applied a few days after 50% early anthesis.

Effects of Pre- and Postanthesis Applications of Demethylation Inhibitor Fungicides on Fusarium Head Blight and Deoxynivalenol in Spring and Winter Wheat

Anthesis is generally recommended as the optimum growth stage for applying a foliar fungicide to manage Fusarium head blight (FHB) and the Fusarium-associated toxin deoxynivalenol (DON) in wheat. However, because it is not always possible to treat fields at anthesis, studies were conducted to evaluate pre- and postanthesis treatment options for managing FHB and DON in spring and winter wheat. Network meta-analytical models were fitted to data from 19 years of fungicide trials, and log response ratio ([Formula: see text]) and approximate percent control ([Formula: see text]) relative to a nontreated check were estimated as measures of the effects of six treatments on FHB index (IND: mean percentage of diseased spikelets per spike) and DON. The evaluated treatments consisted of either Caramba (metconazole) applied early (at heading [CE]), at anthesis (CA), or late (5 to 7 days after anthesis; CL), or Prosaro (prothioconazole + tebuconazole) applied at the same three times and referred to as PE, PA, and PL, respectively. All treatments reduced mean IND and DON relative to the nontreated check, but the magnitude of the effect varied with timing and wheat type. CA and PA resulted in the highest [Formula: see text] values for IND, 52.2 and 51.5%, respectively, compared with 45.9% for CL, 41.3% for PL, and less than 33% for CE and PE. Anthesis and postanthesis treatments reduced mean IND by 14.9 to 29.7% relative to preanthesis treatments. The estimated effect size was also statistically significant for comparisons between CA and CL and PA and PL; CA reduced IND by 11.7% relative to CL, whereas PA reduced the disease by 17.4% relative to PL. Differences in efficacy against IND between pairs of prothioconazole + tebuconazole and metconazole treatments applied at the same timing (CE versus PE, CA versus PA, and CL versus PL) were not statistically significant. However, CA and CL outperformed PA and PL by 7 and 12.8%, respectively, in terms of efficacy against DON. All application programs had comparable efficacy against IND between spring and winter wheat types, but efficacy against DON was 10 to 16% greater for spring than winter wheat for applications made at or after anthesis. All programs led to an increase in mean grain yield and test weight relative to the nontreated check.

Dissipation of plant protection products from foliage

In the environmental risk assessment for plant protection products in the European Union a default foliar dissipation half-life (DT50) of 10 d is used for the risk assessment of herbivorous birds and mammals feeding on sprayed foliage. This generic DT50 of 10 d is based on a compilation of residue trials conducted over 30 yr ago, in which many compounds and formulations were considered that are not used anymore. We therefore reassessed foliar dissipation based on a data set of 396 residue trials covering 30 compounds. Foliar DT50s were calculated, and potential factors determining dissipation were analyzed, such as crop group, residue zone, and rainfall. The strongest source of variability was found between individual trials. Other factors, including the residue zone and crop group, did not have a significant impact on dissipation. Only heavy rainfall (>6.5 mm/d, i.e., the 95th percentile of rainfall) had a statistically significant influence, although rainfall explained only approximately 5% of the overall variability. Moderate rainfall (≤6.5 mm/d) did not significantly correlate with dissipation and explained only 0.1% of the overall variability. Most importantly, the differences in DT50s between crops and residue zones were neither marked nor statistically significant; hence, trials from different residue zones and crops could be pooled to obtain more robust half-lives. Over all compounds, trials, zones, and crops the geometric mean DT50 was 3.2 d (90th percentile 7.9 d). Environ Toxicol Chem 2018;37:1926-1932. © 2018 SETAC.

Impact of post-anthesis rainfall, fungicide and harvesting time on the concentration of deoxynivalenol and zearalenone in wheat

Field experiments were conducted to identify the impact of post-anthesis rainfall on the concentration of deoxynivalenol (DON) and zearalenone (ZON) in harvested wheat grain. Winter wheat plots were inoculated with Fusarium graminearum at stem extension (GS31) and prothioconazole was applied at mid-anthesis (GS65) to split plots and plots were subsequently mist irrigated for 5 days. Plots were either covered by polytunnels, irrigated by sprinklers or left as non-irrigated uncovered control plots after medium-milk (GS75). Plots were harvested either when ripe (GS92; early harvest) or three weeks later (late harvest). Fusarium head blight (FHB) was assessed each week from inoculation. At harvest, yield and grain quality was measured and grains were analysed for DON and ZON. Differences in rainfall resulted in contrasting disease pressure in the two experiments, with low FHB in the first experiment and high FHB in the second. Difference in FHB resulted in large differences in grain yield, quality and mycotoxin content. DON concentration was significantly (P < 0.05) higher in irrigated compared to covered and control plots in the first experiment, whereas in the second experiment, DON was significantly (P < 0.05) higher in the covered plots compared to the control and irrigated plots. ZON concentration was significantly (P < 0.05) higher in irrigated plots in both experiments. Later harvesting resulted in an approximate fivefold increase in ZON in the first experiment, but was not significantly different in the second experiment. Prothioconazole significantly (P < 0.05) reduced DON in both experiments, but gave inconsistent reductions to ZON. This is the first report to show that the post-anthesis rainfall can significantly increase ZON in wheat, which can increase further with a delayed harvest but may be significantly reduced with the application of prothioconazole. Importantly, in the absence of moisture late season, ZON remains at very low concentrations even when wheat is severely affected by FHB.

Efficacy of Fungicide Applications During and After Anthesis Against Fusarium Head Blight and Deoxynivalenol in Soft Red Winter Wheat

Seven field experiments were conducted in Ohio and Illinois between 2011 and 2013 to evaluate postanthesis applications of prothioconazole + tebuconazole and metconazole for Fusarium head blight and deoxynivalenol (DON) control in soft red winter wheat. Treatments consisted of an untreated check and fungicide applications made at early anthesis (A), 2 (A+2), 4 (A+4), 5 (A+5), or 6 (A+6) days after anthesis. Six of the seven experiments were augmented with artificial Fusarium graminearum inoculum, and the other was naturally infected. FHB index (IND), Fusarium damaged kernels (FDK), and DON concentration of grain were quantified. All application timings led to significantly lower mean arcsine-square-root-transformed IND and FDK (arcIND and arcFDK) and log-transformed (logDON) than in the untreated check; however, arcIND, arcFDK, and logDON for the postanthesis applications were generally not significantly different from those for the anthesis applications. Relative to the check, A+2 resulted in the highest percent control for both IND and DON, 69 and 54%, respectively, followed by A+4 (62 and 52%), A+6 (62 and 48%), and A (56 and 50%). A+2 and A+6 significantly reduced IND by 30 and 14%, respectively, relative to the anthesis application. Postanthesis applications did not, however, reduce DON relative to the anthesis application. These results suggest that applications made up to 6 days following anthesis may be just as effective as, and sometimes more effective than, anthesis applications at reducing FHB and DON.