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Dimethomorph to prevent rapeseed downy mildew
Downy mildew is a widespread 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 more frequently in cool, wet, or rainy weather conditions. To identify the most effective pesticides for controlling 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% metalaxyl-manganese zinc wettable powder, and 75% chlorothalonil wettable powder. During the flowering stage of the rapeseed, each pesticide was diluted to the recommended concentration and applied. Disease severity was assessed before treatment and at 7, 14, and 21 days post-application. The corrected control effect of each treatment was then calculated.
According to the findings, all six pesticides showed some level of efficacy against downy mildew. Seven days after application, the 80% dimethomorph wettable powder at a 2500-fold dilution achieved the highest corrected control effect of 51.93%, which was significantly higher than the 30% dimethomorph WP at 800 times dilution and the 25% metalaxyl-manganese zinc WP at 500 times. In contrast, the 72% mancozeb-manganese zinc WP at 600 times had the lowest correction rate at 32.21%.
At 14 days post-treatment, the 72% mancozeb-manganese zinc WP at 600 times showed the best performance with a corrected control effect of 32.21%, outperforming the 77% copper hydroxide WP at 800 times, though not significantly different from other treatments. The 80% dimethomorph WP at 2500 times came second with 46.28%.
By day 21, the 72% mancozeb-manganese zinc WP at 600 times once again led with a corrected control effect of 62.17%, which was significantly better than the 77% copper hydroxide WP at 800 times, but not markedly different from other treatments. The 80% dimethomorph WP remained strong with a 46.28% control effect.
Overall, the 72% mancozeb-manganese zinc WP demonstrated high long-term effectiveness, although its initial response was slower. This may limit its use in cases where rapid control is needed. On the other hand, the 77% copper hydroxide WP showed poor control effects over time, suggesting it is less effective against downy mildew. The 80% dimethomorph WP provided the fastest initial response, achieving a 51.93% control effect within seven days and maintaining a 52.72% effect even after 21 days, making it both fast-acting and long-lasting.
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. Based on these findings, the 80% dimethomorph wettable powder appears to be the most effective option for managing downy mildew in rapeseed, offering both quick action and prolonged protection, making it suitable for broader agricultural applications.