Response of sugarcane aphid (Melanaphis sacchari) to interactive effects of soil drenched triterpenoid phytonematicides in sweet sorghum (Sorghum bicolor)

Triterpenoid phytonematicides, namely, Nemarioc-AL, Nemafric-BL and Mordica, when drench-applied each consistently suppressed root-knot nematode population densities, with limited information on whether the products could induce any systemic effects that would suppress sugarcane aphid population densities and reproductive potential. The objective of the study was therefore to determine the interactive effects of soil-drenched triterpenoid phytonematicides on aphid population densities and their reproductive factors. A 2× 2× 2 factorial experiment was laid out in a randomised complete block design with six replications during 2020-21 and 2021-22 growing seasons in Limpopo Province, South Africa. Each sweet sorghum seedling was infested with 5 adult M. sacchari, with appropriate treatment combinations drench-applied weekly. At 150 days after infestation, treatments had highly significant effects on aphid population densities and reproductive factors. Relative to untreated control, the second order interaction and the three first order interactions reduced aphid population densities by 92, 75, 79 and 80%, respectively. In conclusion, soil-drenched triterpenoid phytonematicides induced systemic effects in sweet sorghum, which significantly suppressed population densities of M. sacchari.