Distribution of prothioconazole and tebuconazole between wheat ears and flag leaves following fungicide spraying with different nozzle types at flowering.

BACKGROUND: Wheat ears are difficult targets from the aspect of fungicide spraying. Sideward-spraying nozzle types may enhance the ear coverage, which may possibly lead to higher effectiveness in the management of Fusarium head blight (FHB). RESULTS: On average, sideward-spraying Turbo TeeJet Duo nozzles resulted in 1.30 and 1.43 times higher prothioconazole-desthio and tebuconazole contents and Turbo FloodJet nozzles in 1.08 and 1.34 times higher prothioconazole-desthio and tebuconazole contents in wheat ears by comparison with those achieved with vertically-spraying XR TeeJet nozzles. In contrast, the vertically-spraying XR TeeJet nozzles resulted in 1.57 and 1.31 times higher prothioconazole-desthio and tebuconazole contents in the flag leaf blade. The degradation of the active ingredient (AI) depended on the year, the cultivar and the plant organ, but not on the spraying method. There was no clear relationship between the efficacy of a given nozzle type and the outcome of the FHB epidemic. CONCLUSIONS: The ear coverage and therefore the AI content have been improved with the two sideward-spraying nozzle types. There was no effective translocation of the AI content between the ears and flag leaf blades. Prothioconazole and tebuconazole proved to be highly effective in the management of FHB, but the FHB resistance of the cultivar was also decisive.

Translocation and degradation of tebuconazole and prothioconazole in wheat following fungicide treatment at flowering.

BACKGROUND: Prothioconazole and tebuconazole are among the most effective fungicides against Fusarium head blight (FHB) of wheat (Triticum aestivum L.). The translocation between the ears and the flag leaves and the kinetics of degradation may influence field efficacy of these active ingredients (AIs). RESULTS: In greenhouse experiments, only traces (<1%) of the total AI content translocated from the flag leaves to the ears, and a maximum of 3.55% from the ears to the flag leaves. From the treated to the non-treated side of the ears, 3.2-15.9% of the AI translocated, depending on cultivar, AI and time. In field experiments, the degradation kinetics in the first 8 days after treatment revealed a higher velocity in the flag leaf blades than in the ears, although both were dependent on the type of cultivar. The fungicide treatment resulted in 42.6-100% decreases in FHB traits. CONCLUSIONS: There is no effective translocation of these AIs, only moderate redistribution in the ears, which can be decisive from the aspect of FHB management. The degradation of prothioconazole was faster than that of tebuconazole. Cultivar and environmental effects influenced the degradation kinetics of these AIs, but a high level of protection against FHB was maintained.

Role of fungicides, application of nozzle types, and the resistance level of wheat varieties in the control of Fusarium head blight and deoxynivalenol.

Fungicide application is a key factor in the control of mycotoxin contamination in the harvested wheat grain. However, the practical results are often disappointing. In 2000-2004, 2006-2008 and 2007 and 2008, three experiments were made to test the efficacy of fungicide control on Fusarium Head Blight (FHB) in wheat and to find ways to improve control of the disease and toxin contamination. In a testing system we have used for 20 years, tebuconazole and tebuconazole + prothioconazole fungicides regularly reduced symptoms by about 80% with a correlating reduction in toxin contamination. Averages across the years normally show a correlation of r = 0.90 or higher. The stability differences (measured by the stability index) between the poorest and the best fungicides are about 10 or more times, differing slightly in mycotoxin accumulation, FHB index (severity) and Fusarium damaged kernels (FDK). The weak fungicides, like carbendazim, were effective only when no epidemic occurred or epidemic severity was at a very low level. Similar fungicide effects were seen on wheat cultivars which varied in FHB resistance. In this study, we found three fold differences in susceptibility to FHB between highly susceptible and moderately resistant cultivars when treated with fungicides. In the moderately resistant cultivars, about 50% of the fungicide treatments lowered the DON level below the regulatory limit. In the most susceptible cultivars, all fungicides failed to reduce mycotoxin levels low enough for grain acceptance, in spite of the fact that disease was significantly reduced. The results correlated well with the results of the large-scale field tests of fungicide application at the time of natural infection. The Turbo FloodJet nozzle reduced FHB incidence and DON contamination when compared to the TeeJet XR nozzle. Overall, the data suggest that significant decreases in FHB incidence and deoxynivalenol contamination in field situations are possible with proper fungicide applications. Additionally, small plot tests can be used to evaluate the quality of the field disease and toxin production.