Efficacy and economics of some granular and foliar insecticides against the stemflies (Melanagromyza sojae (Zehtn.) and Ophiomyia phaseoli (Tryon)) attacking soybean.
A study on the efficacy and economics of some granular and foliar insecticides against the stemflies attacking soyabean was conducted in Bangladesh during 1999-2001 cropping seasons. Of the tested insecticides, Furadan 5G [carbofuran]-treated plots had the lowest stem tunneling (6.79% in 1999-2000 and 18.24% in 2000-2001) and yielded the highest (1.94 t/ha in 1999-00 and 1.28 t/ha in 2000-2001), followed by Marshal 6G [carbosulfan]-treated plots compared to the highest stem tunneling (11.74% in 1999-2000 and 26.91% in 2000-2001) and lowest yield (0.60 t/ha in 1999-00 and 0.40 t/ha in 2000-2001) in the untreated control plots. Furadan 5G-treated plots offered the highest benefit cost ratio (BCR) (1.92 in 1999-2000 and 1.40 in 2000-2001), closely followed by Marshal 6G-treated plots. The lowest BCR (-0.11 in 1999-2000 and 0.05 in 2000-2001) was obtained from Diazinon 60EC-treated plots. Granular insecticides protected better than foliar insecticides. A strong negative correlation was found between yield and percentage of stem tunneling, where percentage of stem tunneling attributed 92% (R2=0.92) influence on the yield. The percentage of infested plants on plant age had a positive correlation (r=0.94). A second order polynomial regression was found between larval incidence and plant age, and percentage of stem tunneling and plant age. In these situations, larval incidence and percentage of stem tunneling reached its peak at 46-60 days after sowing.