Effect of thiamethoxam on growth, biomass of rice varieties and its specialized herbivore, Scirpophaga incertulas Walker

Pesticides employed as seed treatment provides protection to seedlings against insect pests and diseases. Seed treatment of five rice varieties with thiamethoxam, an active ingredient of Actara 25 WG, showed positive effects on seed emergence, plant root and shoot biomass and reduction in dead heart damage under both controlled and greenhouse conditions. Under controlled condition thiamethoxam increased emergence in all of the rice varieties tested. The highest dose i.e., 2.0 g L−1of thiamethoxam had the maximum positive effects. The plant shoot and root characters were also influenced positively by the seed treatment. The total root length was superior with measurements of 38.6, 26.5 and 27.4 cm at 2.0 g L−1concentration treatment for the rice varieties Ptb 33, AD09219 and AD07073 respectively. Similarly the root shoot ratio also increased positively at the prominent dosage for the varieties Ptb 33, AD07073 and AD09219 showing ratios of 0.402, 0.415 and 0.420 respectively. However, thiamethoxam seed treatment even at 0.50 g/L concentration showed significant difference over the untreated control in all the rice varieties tested. With respect to biomass (fresh and dry root and shoot weight) all the treatment doses of thiamethoxam was superior over the control in which the dose 2.0 g/L showed prominent fresh root and shoot weight in all the three tested varieties. Thus the thiamethoxam seed treatment except at the minimum dose showed increased shoot weight and root weight compared to untreated control. Considering the effect of thiamethoxam on insect pest, the spray application @ 0.2, 0.4, and 0.6 g/L of thiamethoxam 25WG significantly reduced the dead heart damage symptom caused by yellow stem borer in the all the varieties (TN1, Ptb33 and AD09219) tested compared to control treatment. Thus, the present investigation suggests that the bioactivator thiamethoxam when employed as a seed treatment plays a critical role in rice growth and development.