Effectiveness of fungicides against Asian rust in soybeans revealed

The efficacy results of fungicides against Asian rust from the last harvest were released during the Brazilian Soybean Congress. The studies are conducted by a network of 23 research institutions in several Brazilian states.

The disease, caused by Phakopsora pachyrhizi, compromised up to 63% of the leaf area in untreated areas.

The best result was from pesticides, with a 75% reduction in severity and a productivity of 4.028 kg/ha. This result is an average of the results found in 11 states.

The V130A mutation, associated with reduced efficacy of prothioconazole and tebuconazole, was detected in several regions. Despite this, fungicides containing these ingredients still performed satisfactorily when used in multi-site mixtures. The addition of these products, such as mancozeb or chlorothalonil, showed a significant increase in efficacy and reduced plant damage.

The higher productivity observed in the treatments surpassed that of crops without chemical control by up to 25%. The isolated use of active ingredients, on the other hand, was less effective. Cyproconazole, for example, achieved only 18% control.

The study reinforces the importance of rotating active ingredients and using mixtures with multi-site fungicides to preserve product efficacy and delay pathogen resistance. Sequential applications and repeated use of similar molecules are not recommended.

The study used a standardized protocol, with four applications beginning approximately 46 days after plant emergence. Evaluations were made between the R5 and R6 stages of the crop, a critical phase for determining yield.

The results were published in Embrapa’s Technical Circular 219.

control alternatives

The late presence of the disease in several regions, favored by the sanitary vacuum and early sowing, demonstrated the effectiveness of integrated management strategies.

During the presentation of the figures, researcher Cláudia Godoy, from Embrapa Soja, said that there is a joke that the best strategy against Asian rust is "escape".

"'Escape' is a triple mix of three active ingredients: early crop, early cultivar, and early sowing. This is an old recommendation, but it's being used more frequently due to the growth of second-crop corn. The vast majority of areas are experiencing 'escape' from rust, the best control available," explained Cláudia.