The effectiveness of the fungicides Folicur(R) (a. i. tebuconazole) and Sportak(R) (a. i. prochloraz) applied either separately or in combination was tested in field experiments in 1995 and 1996 against Fusarium head scab. Wheat plants were inoculated artificially with a conidia suspension (5 x 10(5) spores . ml(-1)) of Fusarium culmorum (isolate F. c. 46) mid of flowering (GS 65). Besides the development of Fusarium head scab, grain yield, thousand-grain weight (TGW) and deoxynivalenol (DON) content in the grain were determined. In 1995, head scab diseases in infected control plants of the cv. 'Greif' continuously increased until 26 days after inoculation (dpi) and reached a disease index of 7.9. All Folicur(R) and Sportak(R) treatments reduced disease severity compared to the infected control. The early postinfectional applications (2 dpi; GS 65) proved to be most effective. Folicur(R) diminished disease severity by 56 % and Sportak(R) by 41 %. The early preinfectional (8 dai; GS 60) and the late postinfectional (9 dpi, GS 69) applications were less effective. The fungicide treatments resulted in higher grain yields as compared to the inoculated control. The early postinfectional (2 dpi: CS 65) application affected yield more than the late postinfectional (9 dpi: GS 69) and the early preinfectional Fungicide treatments. The TGWs showed similar tendencies as the grain yields. The severe Fusarium head scab symptoms in cv. 'Greif of the inoculated control variant were associated with a high DON content (27 mg.kg(-1)) in the grain. The DON contents in the grain of the fungicide-treated variants were reduced related to the inoculated control; the most distinct reduction by 71 % was obtained by the combined treatment 2 dpi. In 1996, field experiments with the two winter wheat cvs. 'Kontrast' and 'Pegassos' on two different sites were carried our. Both fungicides were applied exclusively 2 dpi. At the site Karlshof, the more sensitive cv, 'Kontrast' exhibited 31 dpi a disease incidence of 91 % and a disease index of 6.1; the less sensitive cv. 'Pegassos' showed a disease incidence of 67 % and a disease index of 4.4. Of tbe fungicide treatments, the combined application suppressed disease development most effectively; the disease incidence of the cvs. 'Kontrast' and 'Pegassos' was diminished by 52 and 64 %, respectively; the disease index in both cultivars was 2.8. Fusarium head scab reduced in both cultivars the grain yield by 29 % as compared to the not inoculated control. Folicur(R) treatments increased grain yields in the cvs. 'Kontrast' and 'Pegassos' by and 22 %, respectively, and Sportak(R) applications by 17 and 18 %. The combined treatment resulted in the highest yield increases: 31 % in cv. 'Kontrast' and 29 % in cv. 'Pegassos'. DON contents in the grain of the cv. 'Kontrast' and 'Pegassos' were 11.77 and 8.11 mg . kg(-1), respectively. Single Folicur(R) treatments diminished DON content in the grain as compared to the infected control in the cvs. 'Kontrast' and 'Pegassos' by 55 and 49 %, respectively; Sporcak(R) treatments by 43 and 42 % and the combined applications by 61 and 62 %. Similar results were obtained with both cultivars on the field site Neuhausen. The studies indicate that fungicide treatments may nor always bt sufficient to reduce both Fusarium head slab and trichothecene contaminations in the grain of wheat. Research demands include e. g., improving predictions of infection probabilities, fungicide formulations and application techniques as well as combining trichothecene biosynthesis inhibitors with fungicides.
