The effect of the systemic insecticide phorate on vegetative growth and yield of tomato (Lycopersicum esculentum Mill.) was studied in the greenhouse. Three dosages of phorate (1.5, 7.5, and 13.5 mg a.i./ 1.5 L pot) were applied along with a control (without insecticide application). The plants were harvested at 17, 32, 51, 69, and 90 days after tilling. Regression analysis did not show any significant effect of insecticide dosages in plant and root length. However, an overall negative effect of phorate was observed on leaf area, shoot and root dry weights, and fruit fresh weight. Based on multiple regression models, maximum leaf area was obtained with 6.7 mg a.i./pot and maximum shoot and root dry weights were obtained with no insecticide application and 0.1 mg a.i./pot, respectively. Higher fruit fresh weights were also obtained without phorate application. Dosages of phorate close to the lower range recommended for pest control in tomatoes (1 kg a.i./ha) favored the increase in leaf area in tomato plants, but this increase did not cause higher yields. Phorate was slight detrimental to shoot and root growth, what led to a smaller yield in the phorate treated plants.
Tomato; systemic insecticide; vegetative growth
