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Dimethomorph to prevent rapeseed downy mildew
Downy mildew is a widespread and destructive disease that affects rapeseed throughout its entire growth cycle. It leads to leaf death, malformed and weak inflorescences, and can significantly reduce yield and quality. The disease is primarily caused by infection from downy mildew pathogens, and it tends to develop rapidly under cool, wet, or rainy weather conditions. To identify the most effective pesticides for managing this disease, a field trial was conducted using six different pesticide formulations.
The selected products included 72% mancozeb wettable powder, 30% dimethomorph wettable powder, 80% dimethomorph wettable powder, 77% copper hydroxide wettable powder, 25% chlorothalonil wettable powder, and 25% metalaxyl-manganese zinc wettable powder. During the flowering stage of rapeseed, each pesticide was applied at the recommended dilution rate. Disease severity was evaluated before treatment and at 7, 14, and 21 days post-application. The corrected control effect was calculated for each treatment to assess effectiveness.
According to the pesticide network, all six tested products showed some level of control against downy mildew. Seven days after application, the 80% dimethomorph wettable powder diluted at 2500 times had the highest corrected control effect at 51.93%, which was significantly better than 30% dimethomorph WP at 800 times and 25% metalaxyl-manganese zinc WP at 500 times. The 72% mancozeb-manganese zinc WP at 600 times had the lowest control effect at 32.21%.
At 14 days post-treatment, the 72% mancozeb-manganese zinc WP at 600 times showed the best correction effect at 32.21%, outperforming the 77% copper hydroxide WP at 800 times. However, the difference between treatments was not statistically significant in most cases. The 80% dimethomorph WP at 2500 times followed with a 46.28% control effect.
By day 21, the 72% mancozeb-manganese zinc WP at 600 times achieved the highest corrected control effect of 62.17%, which was significantly higher than the 77% copper hydroxide WP at 800 times. The 80% dimethomorph WP at 2500 times came second with 46.28%. The 75% chlorothalonil WP showed moderate results, with corrected control effects of 39.21%, 41.11%, and 49.46% at 7, 14, and 21 days, respectively.
Overall, the 72% mancozeb-manganese zinc WP demonstrated strong long-term control but lacked immediate efficacy, making it less suitable for rapid outbreaks. The 77% copper hydroxide WP had the poorest performance, suggesting it may not be an effective choice for controlling downy mildew. In contrast, the 80% dimethomorph wettable powder provided quick action and maintained high control levels over time, making it a highly effective option for farmers. Based on these findings, the 80% dimethomorph formulation is recommended for use in rapeseed production due to its balanced performance in both speed and duration of control.