The Phytotoxic Effects of Methomyl and Imidacloprid Insecticides on Tomato local Variety in Al-Hassa, Saudi Arabia

Abstract

Imidacloprid and Methomyl are systemic insecticides used widely for controlling insects infesting crops grown in greenhouses. The experiment was conducted on tomato (Hassawi, Local Varity in Eastern part of Saudi Arabia) to study the phytotoxicity effect of the tested insecticides at various application rates. Imidacloprid was tested at (25, 50, 100, and 150 active ingredient (a.i) g/100L water), and Methomylat (15, 35, 50 and 70g a.i/100L). Both insecticides were shown to have negative effect on the growth of old and new parts (stem, leave and shoot) of tomato variety used for the experiment. The symptoms of leaf chlorosis of the old leaves and distorted growth and marginal necrosis of newer leaves were developed after 3 days of application with the highest rate for both insecticide experiments. When application at the lower rate, the phytotoxicity symptom was developed within the second week of application. The size of the new shoot was affected by high rate of application for both Imidacloprid and Methomyl and that was reflected in the reduction of the weight of dried shoot. In case of old leaf, despite the significant differences between the treatment and the reduction in dry weight in correlation with application rates were small. However, the lowest application rates of both tested insecticides showeda positive stimulation in the new growth that emerged after treatments, even though the lowest rate at (25g a.i/100L) of Imidacloprid caused some phytotoxicity symptoms by the end of the experiment. The results indicated the higher phytotoxicity of Imidacloprid than Methomyland the higher application rate had a significantly higher phytotoxicity effect on tested tomato plant than the lower application rate.