Influence of application timing and droplet size on stripe rust management and residue accumulation in wheat

Stripe rust (SR), caused by Puccinia striiformis f. sp. tritici, causes reduced yield and grain quality. This study evaluated the effect of fungicide application timing and spray droplet size on disease control and fungicide residue accumulation in wheat grain under Uruguayan conditions. Two field experiments were conducted during the 2022/2023 and 2023/2024 growing seasons using an SR susceptible cultivar. Disease control was determined by application timing as the main factor, while droplet size (fine vs. coarse) had no consistent effect, suggesting that coarse droplets can be used to reduce spray drift without compromising efficacy. Regarding residual effect, fungicide residue analysis revealed that epoxiconazole exceeded the maximum residue limit (MRL) in treatments involving multiple or late applications in the crop cycle, where pre-harvest intervals were not respected. Fluxapyroxad and pyraclostrobin remained below their respective MRLs in all treatments. Overall, optimizing fungicide application timing is essential to achieve effective control of SR while minimizing residue accumulation in grain, thereby supporting more sustainable and food-safe wheat production systems.