The damage is characterized by rotting tissues of the stem. They become soft and reddish-brown in color. External symptoms are only observed by minute oviposition and feeding punctures at the base of leaf lamina. Plants of 5 - 8 cm height get infested. The stem diameter may be reduced as well as the plant's height (dwarfism). When infested in the productive phase, pods are reduced resulting in fruit loss.
The symptoms are mostly caused by the larvae of the soybean stem miner, Melanagromyza sojae. The adults are characterized as small black flies. Female stem miners lay their eggs in the soil near plant tissues. After the larva hatches, it bores itself in the stem and feeds upward or downward to the roots. This movement may lead to the withering of the top. At a later stage, the grown larva exists in the stem, fills the hole with debris and pupates near the hole it created. When cutting the stem open, the feeding tunnels are visible. It is observed that the 2nd and 3rd generation will create greater damage. M. sojae rarely kills the host plants but can cause economic yield losses. The later the infestation happens, the lower the yield loss will be. It is reported that Ophiomyia phaseoli causes severe damage before M. sojae which implies that the damage cannot be 100% linked to M. sojae. The soybean stem borer is detected across diverse eco-climatic zones and has been attacking various legume/pulse species.
M. sojae has a large number of predators and other natural enemies, which is frequently sufficient to control its spread. Parasitoid wasps like Cynipoidea sp., Sphegigaster sp., Eurytoma melanagromyzae, Syntomopus carinatus, and Aneuropria kairali will control the pest by 3% in Sphegigaster sp. to 20% in E. melanagromyzae. Cynipoidea sp. and E. melanagromyza may be used in integrated pest management methods.
Always consider an integrated approach with preventive measures together with biological treatments. It is important to implement measures either at sowing as a soil treatment or immediately after germination by foliar spraying with either Lambda-Cyhalothrin 4.9% CS, Thiamethoxam 12.6% ZC and Lambda-Cyhalothrin 9.5% ZC or Indoxacarb 15.8% EC.