Interactions Among Nitrogen Rates and Foliar Fungicides Affect the Agronomic Performance of Soft Red Wheat Varieties.

The simple effects of nitrogen rates, fungicide application, and varietal responses on wheat yield and quality have been studied individually, but interactions among the inputs have been largely ignored.  Traditionally, increased nitrogen rates have led to higher risk of lodging and disease severity (Roth and Marshall, 1987), but it has been found that fungicides can be used to delay the onset of disease (Gooding et al. 1999).  Similarly, yield responses to application of a fungicide may be affected by available nitrogen (Olesen et al., 2003).  Recent Ontario research shows strong interactions between fungicide and wheat varieties, even in the absence of disease, but the relationships are poorly understood.  Current field crop recommendations would be improved by knowledge of interactions between inputs in more intensive management systems.  A series of field experiments was established on three farm fields in each of three years in southwestern Ontario to investigate possible interactions among nitrogen rates, fungicides, and varieties.  The experimental design at each field was a factorial arrangement of three nitrogen rates (100kg/ha, 135 kg/ha, and 170kg/ha with a growth regulator) and three different fungicide timings (with or without fungicide at Zadoks growth stages 30, 45-49, and 60-65) across six top soft red wheat varieties.  Measurements included leaf disease severity, fusarium head blight incidence and severity and mycotoxin concentrations, NDVI canopy measurements, and grain yield components.  An economic analysis was performed on the combinations of treatment variables toward the development of more comprehensive recommendations.  These results will be augmented with a subset of these treatment combinations on at least 50 field-scale trials across southern Ontario.  This research will assess the economic viability of several intensive-management practices available to Ontario wheat growers, and will provide more comprehensive recommendations on intensive wheat management practices in Ontario.