Research analyzes the effectiveness of fungicides against wheat powdery mildew

Wheat powdery mildew advances rapidly after plant emergence. With short and multiple cycles, the fungus blumeria graminis f.sp. tritici can compromise up to 62% of productivity. Faced with this constant threat, chemical management becomes essential. In the 2024/25 harvest, the Cooperative Wheat Trials Network tested seven fungicide treatments in 11 locations in southern Brazil. The results indicate that all the products tested were effective, although at different levels.

The most effective treatments contained tetraconazole alone, and a mixture of tetraconazole, azoxystrobin, tebuconazole and chlorothalonil. Both significantly reduced disease severity.

The disease appeared in all trials. The average severity recorded was 38%, with a peak of 93,8% in the municipality of Coxilha (RS). The areas of greatest pressure also presented the highest accumulated values ​​of severity over time, measured by the area under the disease progress curve (AUDPC). In Coxilha, the AUDPC reached 280. In contrast, Cruz Alta (RS) recorded the lowest value: 22,7.

Chemical control reduced the average severity from 33,9% (control without fungicide) to 4,3% in the case of one of the treatments, which obtained 87,3% efficiency.

The experiments included cultivars with different levels of resistance. Even moderately resistant varieties were severely affected in regions with high incidence of the disease. This phenomenon raises hypotheses about the emergence of new races of the pathogen or failures in the classification of resistance of cultivars. These variations reinforce the need for constant adjustments in technical recommendations.

The methodology adopted was rigorous. The trials followed a randomized block design, with four replicates and a minimum area of ​​11 m² per plot. Applications occurred at two times: at tillering or when the first symptoms appeared (up to 5% severity) and 14 days later. Spraying was done with precision and at a volume of 150 L/ha.

Statistical analysis used mixed linear models, considering fixed effects of treatments and random variables related to sites and cultivars. Data were transformed to meet statistical assumptions. Comparisons followed the Tukey test with 5% significance.

Despite the good performance of fungicides, the study warns: alternating active ingredients with different mechanisms of action is essential. Repeated use of the same ingredient favors the emergence of resistant variants. The recommendation follows guidelines from the Fungicide Resistance Action Committee (FRAC-BR).