FOLIAR SPRAY OF POTASSIUM SILICATE ON THE CONTROL OF ANGULAR LEAF SPOT ON BEANS

This study aimed to determine if potassium silicate (KSi) sprays could reduce the intensity of angular leaf spot. In field experiment 1, bean plants were sprayed with KSi (pH 10.5) at rates of 8, 20, 40, and 60 g L^?1. In field experiment 2, with the same treatments, the pH of the KSi solutions was 5.5. In experiment 3, the treatments were KSi (40 g L^?1, pH 5.5), potassium hydroxide (KOH) (6.5 g L^?1, pH 5.5), tebuconazole (0.5 L ha^?1), and control. In experiment 4, the treatments were the same as in experiment 3, but the pH of the KSi and KOH solutions was 10.5. Plants sprayed with water served as a control treatment for all field experiments. Plants were artificially inoculated with Pseudocercopora griseola before products application. For experiments 3 and 4, the treatment with KOH was included to equalize the amount of potassium (K) with the treatment corresponding to the application of KSi. Disease severity was evaluated using a scale with values ranging from 0.2 to 30.4% at 85 days after seedling emergence. Plant defoliation, Si, and K concentration in the plant tissues, and yield were also determined. There was no relationship between KSi rates and Si concentration in leaf tissues, but Si concentration increased by 58 and 57%, respectively, as the KSi rates increased from 0 to 60 g L^?1 regardless of the pH. The K concentration in leaf tissues did not change among the treatments. Disease severity decreased by 42 and 30%, respectively, at the highest KSi rate with pH 5.5 and pH 10.5 over the control. Disease severity levels were similar between the KSi and KOH treatments, but they were significantly higher compared to the tebuconazole. Plant defoliation at the highest KSi rate with pH 5.5 and 10.5 was 17 and 33%, respectively, less than the control. Plant defoliation decreased with the application of KSi with pH 5.5 and 10.5 in 29 and 34%, respectively, compared to the control. Yield increased by 30 and 43%, respectively, as the KSi rates increased from 0 to 60 g L^?1with pH 5.5 and 10.5. No statistical difference in yield was detected between the KSi and KOH treatments regardless of the pH used, but both were different from tebuconazole. Significant differences in yield were found only between tebuconazole and the control. Results from this study suggest that foliar application of KSi and KOH has the potential to reduce angular leaf spot severity. The KSi did not offer any advantage over the KOH spray, suggesting a lack of a direct effect of Si accumulated in the leaf tissue on disease control.