Comparing the Effectiveness of Different Acaricides on the Control of Two-Spotted Spider Mite, Tetranychus urticae Koch., at Different Population Densities in Bean Fields of Lordegan Region

The goal of this investigation was to study the effectivenessy of different acaricides on the control of twospotted spider mite (TSSM) at different mite population densities. Study was conducted based on the randomized complete block design (RCBD) using split plot experiment. When the pest population exceeded 3, 5 and 7 mites on the abaxial surface of each leaf in the main plot, spraying was done by sub plot treatments including: fenazaquin (Pride® SC 20%) at the rate of 0.5 lit/ha, fenpyroximate (Ortus® SC 5%) at the rate of 0.5 lit/ha, bromopropylate (Neoron® EC 25%) at the rate of 2 lit/ha and only water as control. Sampling was done 1 day before, 3, 7 and 14 days after each spraying. For sampling, 30 leaves were selected randomly from each treatment and the number of mites (adults & nymphs) was counted at 2 cm² area of under surfaces of the leaves. Mortality percentage of mites was calculated using Abbot and Henderson Tillton formulas. After normalizing the data, mean comparison was carried out using Duncan Multiple Range Test. Results indicate significant differences among the main plot factors, and treatment in the 1st and 2nd levels (3 and 5 mites on abaxial surface of each leaf, respectively) was more effective than the 3rd level 7 mites on abaxial surface of each leaf). Mean comparison of the mite mortality among different acaricides showed that bromopropylate with 97.8 and 95.8% mortality at day 14 (in the 1st and 2nd sampling time, respectively) was more effective than fenazaquin and fenpyroximate. It could be concluded that taking population density of the pest into consideration for choosing the right spraying time can increase the effectiveness of the acaricides.