Effects of rate and timing of nitrogen fertilizer on disease control by fungicides in winter wheat. 1. Grain yield and foliar disease control

Abstract

SU MMARYThe effects of nitrogen (N) rate and timing on need for fungicide application in winter wheat (Triticum aestivum) were investigated in 3 years of field experiments on loamy sand soils in Denmark. A two-factor completely randomized experimental design was used, comprising seven combinations of different N fertilizer rates and application times, and five doses of fungicide (co-formulation propiconazole and fenpropimorph). Two different varieties of winter wheat with high susceptibility to powdery mildew (Blumeria graminis) were used, Florida in the first season and Pepital in the last two seasons. The severity of powdery mildew and septoria leaf spot (mainly Septoria tritici) varied between seasons from slight to moderate with powdery mildew dominating in the first season and septoria leaf spot in the last season. The severity of both powdery mildew and septoria leaf spot assessed as the Area Under the Disease Progress Curve (AUDPC) was increased by application of N in all years, and more so by early applied N. Grain yields increased with increasing N rate and fungicide dose. However, the observed grain yields did not reveal any Nrfungicide interactions. Regression models were therefore fitted, relating grain yield to rate and timing of N fertilizer and to AUDPC of powdery mildew and septoria leaf spot, and relating AUDPC to rate and timing of N fertilizer and to fungicide dose. They demonstrated that septoria leaf spot had a considerably higher impact on grain yield than mildew. The optimal fungicide dose and N rate were defined as those giving the highest economic return. The regression models were used to estimate the effect of N rate and timing on optimal fungicide dose, and the effect of fungicide application on optimal N rate. The optimal fungicide dose increased almost linearly with N rate above a minimum N rate, but with a large dependency on price relations. Early applied N caused a higher demand for disease control. The fungicide applications in the model were mainly driven by the need to control septoria leaf spot, whereas powdery mildew gave a poor net return for control. The estimated optimal N fertilizer rate for untreated diseased crops was 60 kg N/ha lower than for crops without disease. The use of fungicides with an efficacy twice that of the EBI-fungicides used in this experiment would increase the optimal N rate by c. 20 kg N/ha.

Synergism of Nitrogen Rate and Foliar Fungicides in Soft Red Winter Wheat

“…This result contrasted with similar comparisons in the literature; several have reported high concentrations of N in the canopy favored leaf rust (Walters and Bingham, 2007), powdery mildew (Olesen et al, 2003a), and septoria (Howard et al, 1994; Lovell et al, Table 10. UTC, untreated check no fungicide; T3, fungicide at Zadoks Growth Stage (GS) 65; T123, fungicide at approximately GS 30, GS 39, and GS 65.…”

“…At Ridgetown and Lucan in 2010, the maximum yields were produced with N rates between 100 to 170 kg N ha -1 with the T123 fungicide treatment; yields declined at the highest rate of N where no fungicides were applied (likely in part due to lodging and harvest losses at these two sites). The difference in response between the UTC and the T3 and T123 fungicide treatments suggests that the most economical rate of N may vary with efficacy of disease control by fungicides, as reported by others (Olesen et al, 2003a;Berry et al, 2010).…”

“…1997). However, Olesen et al (2003a) in Denmark reported no correlation between N rate and septoria. Higher rates of N tend to produce larger canopies that provide more favorable environments for pathogenic infection (Walters and Bingham, 2007).…”

Influence of Various Wheat Genotypes and Agriculture Practices on Powdery Mildew Incidence

“…Powdery mildew is most severe on wheat grown in soils with high nitrogen content (Emam et al, 2010). The dense growth which resulted from excessive nitrogen fertilizer will from creates ideal environmental conditions for disease development (Olesen et al, 2003). Nitrogen application commonly increases leaf Nitrogen concentration, with contrasting effects on disease severity (Simón et al, 2003).…”

“…Wheat cultivation under periods of water deficit can significantly decrease yields (Emam et al, 2010;Roberto et al, 2012). There are very few reports studying the effect of irrigation on disease levels, although drought to increase the adult plant resistance to powdery mildew, which transmitted by rain splash, it might be affected by nitrogen supply and irrigation strategy (Olesen et al, 2003;Epstein and Bloom, 2005). Irrigation contributed to the emergence of leaf diseases.…”