Persistence of Chlorothalonil in Spinach Cultivated under Open and Protected Conditions

Agricultural practices often include the use of pesticides to enhance crop yields. The use of pesticides in agriculture has become necessary and is essential in the modern concept of scientific farming. In recent years however due to increase in consumer demand and increasing pest incidence, some pesticides are used even on low value leafy vegetable crops. Incidence of pesticide residues is more on leafy vegetables as these crops are harvested frequently and consumed fresh and sometimes raw. Also surface area of these crops is often more hence initial deposit of pesticide spray is higher. There is an increasing demand for good quality, safe vegetables in the market. To reduce pesticide residue load on fresh produce pre-harvest interval (PHI) or safe waiting periods have been recommended for vegetables. Also, for every pesticide maximum residue limits (MRLs) are fixed. To achieve these levels a time gap has to be maintained between the last spray of pesticide and the first harvest of crop. This time gap is known as the pre harvest interval (PHI) or waiting period. To calculate PHI, persistence study of pesticides on crops are conducted in the field by following good agricultural practices. Chlorothalonil, 2,4,5,6-tetrachloro-1,3 benzene dicarbonitrile, is a broad spectrum polychlorinated contact fungicide, first registered in U.S.A. for use on potatoes for the control of early blight and late blight in 1969. Registration for use on seventeen additional economically important vegetable and field crops was accepted in 1971 [1]. The compound is extensively used for control of wide variety of fungal diseases in different crops. It is effective against all four classes of fungi namely Oomycetes, Ascomycetes, Basidiomycetes, Fungi Imperfecti. It controls leaf spots, rust, blights, fruit rot, mildews and scab [2, 3, 4]. Chlorothalonil is used for control of leaf spot diseases in spinach. Fate of chlorothalonil needs to be evaluated in leafy vegetables like spinach so that their safe use can be recommended. This study was therefore carried out to determine safe waiting period for chlorothalonil in spinach and also to explore ways to accelerate residue dissipation in spinach after the pests have been controlled. A microbial consortia developed at IIHR [5] has shown excellent results in increasing vegetative growth of vegetables, thus we Abstract Persistence of chlorothalonil in spinach by following application of commercial formulation of chlorothalonil (Kavach 75% WP)@50 g a.i.ha -1 in field and polyhouse with and without biofertiliser is reported. Samples of spinach beet drawn periodically after application of chlorothalonil were analysed by GC-ECD. The residues of chlorothalonil in spinach dissipated by almost 80% in 5 days with a half life of 2.03 days in field grown biofertiliser treated crop and 2.12days in polyhouse grown biofertiliser treated crop whereas in case of bio-fertiliser untreated crop the half life was 2.40 days and 2.76 days in field and polyhouse respectively. The pesticide persisted little more in biofertilizer untreated crop than in treated crop. Also, the residues persisted longer in polyhouse than in open field. The bio-fertilizer used in this study helped increase yield without harming the environment and also resulted in lower residue levels.