Nitrogen Fertilization and Its Interaction with Leaf Diseases and Fungicide Use Strategies in Wheat.

The intensive use of N fertilizers to maximize yields increase susceptibility of wheat (Triticum aestivum L.) to some fungi attack. Field experiments were conducted in INIA-La Estanzuela (Uruguay) to study the interaction between N fertilization and fungicides use. Treatments consisted in a factorial combination of N levels, fungicide applications and genotypes. Fungicide treatments consisted of: 1) no fungicide use, 2) fungicide applications throughout the growing season, 3) strategic fungicide application based on disease infection and weather. When leaf rust was the predominant disease the effect of fungicides increased with increasing N levels. Maximum yields were achieved at the highest N rate with total protection in very susceptible genotypes and early disease attack. With moderate N rates differences between strategic fungicide applications and total protection where in general not significant.  The effect of fungicide on yields was associated with larger, heavier kernels per ear and as a result heavier 1000-kernel weight.