Pirimiphos-Methyl Residues and Control of Greenhouse Whitefly (Homoptera: Aleyrodidae) on Seven Vegetables

Abstract

A gas chromatographic analysis of pirimiphos-methyl, Actellic®, residues on four leafy vegetables (celery, radicchio, cabbage and kohlrabi) and three fruity vegetables (green beans, pepper and cucumber) is reported. The method proved to be accurate and reliable for residue estimation with recoveries of 90–96% from fortified vegetable tissues, depending on the crop species and the part of the plant analyzed. Initial deposition of pirimiphos-methyl and its disappearance rate on the different types of plant surfaces varied widely. Residue disappearance rates varied from rapid on cucumber fruits (t½ = 1.8 d) to slow on pepper fruits (t½ = 4.3 d) over a 42-day period. On leaves, green beans had the highest dissipation rate (t½ = 2.0 d) while pepper had the lowest (t½ = 4.7 d). Waiting periods (preharvest safety intervals) on each crop were also determined. The potential of pirimiphos-methyl was tested as a candidate for greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) control. Cucumber and bean foliage were preferred by greenhouse whitefly. One day following application of Actellic® 5E emulsifiable concentrate at the rate of 4.5 g (AI)/L of liquid spray, whitefly populations were reduced significantly on both cucumber (88%) and beans (96%). Pirimiphos-methyl may be a useful candidate for control of greenhouse whitefly and other insects in home gardens based on its effectiveness and human safety.