Efecto de la pulverización con fungicida sobre el control de la roya estriada y la presencia de residuos en el grano de trigo

Chemical control is the primary management strategy for stripe rust (SR) in wheat, and its effectiveness largely depends on application timing and spray quality. Under highly conducive conditions, multiple applications during the crop cycle may be required, increasing the risk of fungicide residues in grain. The objective of this thesis was to evaluate the effect of droplet size on SR control efficiency using a fungicide mixture and to assess the risk of residue occurrence in wheat grain as influenced by application timing. Two experiments were conducted using a cultivar susceptible to SR. In Experiment 1, a fungicide mixture (fluxapyroxad, epoxiconazole, and pyraclostrobin) was applied using two droplet sizes (coarse and fine) at three application timings: critical threshold (Ct), 15 days after Ct, and GS49. Disease control and grain yield were evaluated. In Experiment 2, the same mixture was applied with both droplet sizes at different crop growth stages, simulating scenarios with a high risk of residue occurrence in grain. Stripe rust was first detected at GS41 and reached a maximum severity of 26%. Although differences in disease levels were observed among treatments, control efficiency and yield showed limited variation. The application performed at Ct did not achieve the expected level of control, likely due to the spatial heterogeneity of the epidemic and the environmental conditions following application. These findings highlight the importance of continuous monitoring and of adjusting fungicide decisions according to epidemic dynamics and weather forecasts. In Experiment 2, droplet size did not significantly influence fungicide residue concentrations in grain. Applications performed at advanced growth stages and multiple applications that did not comply with the pre-harvest interval exceeded the maximum residue limits established by international regulatory bodies. Overall, the results emphasize the importance of timing fungicide applications based on pathogen detection and predicted conducive environmental conditions, prioritising the use of coarse droplets to minimise spray drift and strictly adhering to label-specified pre-harvest intervals.