Silicon Supply to Barley Reduces Leaf Diseases Intensity and Increases Flexibility of Fungicide Interventions.

Silicon (Si) has been recognized as a beneficial element in plant disease resistance; however, its role under field conditions in barley remains insufficiently explored. This study evaluated the effects of soil-applied Si and its interaction with cultivars and fungicide programs on foliar disease control and yield components in barley over four growing seasons. Two field experiments were conducted: Study I assessed the interaction between Si supply, cultivars, and fungicide application, while Study II evaluated different fungicide programs under Si supply. Silicon application consistently reduced disease severity and the area under the disease progress curve for powdery mildew and leaf spots across cultivars and seasons. The combined use of Si and fungicides resulted in the greatest disease reduction. Cultivar BRS Cauê, showing higher partial resistance than BRS Brau, showed greater responsiveness to Si, which was associated with higher foliar Si concentration. Fungicide programs P2 [sprays at growth stage (GS) 12, GS26, GS37, and GS61] and P3 (sprays at GS12, GS31, and GS 61) were the most effective for disease control and under Si supply. Fungicide program P3, despite one fewer application, achieved disease control comparable to P2, suggesting the potential for optimizing fungicide use under Si supply. Grain yield increases closely followed reductions in disease intensity, with the highest yields observed under combined Si supply and optimized fungicide programs. These findings demonstrate that Si contributes to disease reduction and yield improvement and may serve as a key component of integrated and sustainable disease management in barley.