اثر حشره‌کش‌های امامکتین بنزوات ، کلرپیریفوس و تیودیکارب روی لارو سن سوم آفت برگ‌خوار چغندر (Spodoptera exigua) در منطقه داراب

One of the most significant pests of sugar beet is the beet armyworm (Spodoptera exigua Hubner (Lep. Noctuidae)), whose larval feeding can lead to plant destruction. In 2020, two laboratory and field investigations were conducted in Darab region, Fars, to evaluate the lethal effects of the insecticides emamectin benzoate (Bekchi® SG 5%), chlorpyrifos (Dorsban® EC 40.8%), and thiodicarb (Larvin® DF80%) on 3rd instar larvae of the sugar beet armyworm. To determine the LC50 of these insecticides, lethal doses for 80% and 20% mortality were measured, and five logarithmically spaced doses were established for each insecticide, then LC50 were measured at 48 and 72 hours after treatment under laboratory conditions. The field study compared the effectiveness of emamectin benzoate (160, 200 and 240 ml/ha), chlorpyrifos (1.6, 2 and 2.4 L/ha), and thiodicarb (0.8, 1 and 1.2 L/ha) over four intervals: one, three, seven, and fifteen-days post-application using the Henderson-Tilton formula. Based on the LC50 values at 48- and 72-hours post-treatment, imidacloprid toxicity (21.6 and 35.9 ppm, respectively) was higher than chlorpyrifos (81.52 and 10.64 ppm) and thiodicarb (99.29 and 53.45 ppm). Field experiments showed that the effectiveness of each insecticide decreased over time. The highest mortality was obtained in the emamectin benzoate (240 ml/ha) and the chlorpyrifos treatment (4.2 L/ha), with 76.2% and 73.2%, respectively. Meanwhile, the highest mortality percentage at the 3-day interval was associated with emamectin benzoate (240 ml/h) and thiodicarb (2.1 L/ha), calculated at 72.2% and 76.2%, respectively. At 7 days post-treatment, both emamectin benzoate (240 ml/ha) and thiodicarb (2.1 L/ha) had a mortality rate of 66.7%. Finally, at 15 days post-treatment, emamectin benzoate (240 ml/ha) achieved a 50% mortality rate. Therefore, in the study area, emamectin benzoate demonstrated the highest control efficacy among these insecticides against sugar beet armyworm.