Effects of particle size and active ingredient content on residual activity of chlorpyrifos wettable powder formulations against codling moth,Cydia pomonella (L.)

In a laboratory experiment Cydia pomonella (L.) eggs, two days from eclosion, were placed on apples which had been sprayed five weeks previously with chlorpyrifos (125 mg/litre) from five formulations. Four were wettable powders (250 g a.i./kg) with particles ca 4, 5, 9 and 10 μm in diameter and one (500 g a.i./kg) with particles 2 μm in diameter. The treated apples were aged in direct sunlight. The percentage of apples without deep entries by first instar larvae one week after positioning of eggs, was greater the greater the ratio of active ingredient content of a formulation to total wettable powder particle surface area.