Influence of Potassium, Micronutrients, and Their Combinations as Foliar Applications to Suppress Soybean Stem Fly, Melanagromyza sojae (Diptera: Agromyzidae) on Four Soybean Common Varieties

The present studies followed the main study which was carried out at the experimental farm of the Faculty of Agriculture Benha University, Qalubiya Governorate, during two successive seasons: 2014 and 2015. The influence of potassium, micronutrients, and their combinations as foliar applications to suppress soybean stem fly, Melanagromyza sojae (Zehnt.) (Diptera: Agromyzidae) on four soybean common varieties was studied. The experimental design was a spilt plot with four replications, main plots (i.e., the cultivars Crowford, Giza-22, Giza-35, and Giza-111) and sub plots were assigned to eight. Four soybean cultivars and eight foliar application treatments (potassium silicate, potassium sulphate, potassium hydroxide, micronutrients (Fe, Zn, and Mn), potassium silicates + micronutrients, potassium sulphate + micronutrients, potassium hydroxide + micronutrients and control) were evaluated. The study showed that (potassium silicates + micronutrients) reduced the most impact from the soybean stem fly as indicated by the tunneling length and the number of larvae inside the plant with no significant differences among varieties. There were significant differences in relative increases of seed and stover yield with potassium silicates + micronutrients (25% of the seed yield and 0.30% as an average per two seasons compared to the control). Results also showed a significant increase in the total uptake of potassium with micronutrients for the rest of the treatments; especially with potassium silicate, and perhaps for this reason micronutrients increase the absorption of potassium allowing the plant to build the restoration after the infection. The percentage of lignin content in soybean dry plants resulted in significant increase in all treatments compared with control especially in potassium silicates + micronutrients. Increasing in lignin contents lead to the increase in the secondary xylem and decrease in the pith diameter and then lead to hamper the growth of larva in the pith.