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Head blight (Fusarium graminearum) and deoxynivalenol concentration in winter wheat as affected by pre-crop, soil tillage and nitrogen fertilization.

Fusarium head blight (FHB), caused by F. graminearum, is increasing world-wide. Fusarium mycotoxins are a serious threat of health and a reliable control by fungicides is not possible, yet. The present study was conducted in order to evaluate the influence of different pre-crops and crop husbandry on FHB incidence in winter wheat test crops. In a 2-years factorial field experiment on the experimental station Ihinger Hof of the University of Hohenheim (480 m a. S. 1., loam soil, 7,9 °C, 690 mm), inoculated pre-crops of maize or spring wheat were harvested for silage with only the stubble remaining in the field or for grain by combine with the whole straw remaining. Subsequently, crop residues were left on the soil surface or ploughed under before sowing winter wheat. Nitrogen fertilizer was applied to these test crops with calcium ammonium nitrate (CAN) or nitrolime. FHB was assessed by plot scores, by observations of disease incidence, disease severity and grain infection, indirectly via grain germination and by chemical deoxynivalenol (DON) analyses. The infection by FHB and the grain contamination with DON were similar after maize and spring wheat, either for silage or for grain, but the method of pre-crop inoculation by infected oat grains might have masked differences between pre-crops. The reductions of FHB incidence due to ploughing or nitrolime application were 27-32 % or 31-59 % compared with residues remaining on the surface or CAN fertilization, respectively. Contemporary reductions in DON were less consistent. The assessment of percent infected ears can be recommended as a comparatively fast method for FHB evaluation that showed significant correlations with DON concentration and grain germination, too. But a reliable estimation of DON concentrations is not possible on the basis of infection assessments. In conclusion, crop health can be supported by crop husbandry to some degree, but FHB cannot be reliably controlled in susceptible rotations with abundant sources of inoculum.