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Abstract (85) SUMMARY Tomatoes grown for either summer or winter crop was sprayed with three organophosphorus insecticides; malathion, pirimiphos methyl and profenofos, all the three insecticides being recommended against sap sucking insects on tomatoes. Insecticides were used at the rates of 570 g~a~i. malathion, 750 g~a.i. pirimiphos methyl and 540 g.a.i. profenofos per feddan, all the insecticides used were in commercial emulsifiable concentrate formulations~ Three methods of exraction were tried out and one of them was selected by vertue of its reproduceability and being less complicated~ Residues were cleaned up and determined by gas chromatography for deposits on both fruits and leaves~· Results indicated the following: 1- The largest initial deposit was that of pirimiphos methyl, indicative of the relat.ionship between concentration and initial d4:!posit. When malathion and profenofos were cOJnpared, however, less deposit of profenofos was found, the difference was not proportional to the small difference of rate of application, thus pointing to the probability of the eff~!ct of formulation constituents. (86J 2- In all cases leaves retained more deposits than frutis indicating the effect of weight to surface ratio effect on initial deposit in addition to the effect of the texture of the sprayed surf4ce~ 3- Residues of pirimiphos methyl were the least persistent of the three insecticides investigated, followed by malathion with a rather small difference, while profenofos was conspicuously more persistent than the other two insecticides and this observation W,lS true for both leaves and fruits. 4- In malathion and pirimiphos methyl the deterioration of residues was slightly slower on the winter crop compared to the summer crop nlthough the diference was rather small in mnlathion and slightly more pronounced in pirimiphos methyl;; In profenofos, however, the deterioration rates and pattern were alaost identical in both seasons. 5- The rate of residues decomposition was always faster on and in tomato fruits compared to leaves. This was explained by the fact that initial deposit vas larger on leaves compared to fruits in addition to the difference in (87) texture and its probable effect on the binding nature of the insecticide to them. 6- The tolerance limit for malathion on and in tomatoes is 3 ppm and for pirimiphos methyl is 1 ppm. Residue determination indicated that both limit were surpassed after 12 days in both summer and winter crops, so this period can recommended to slopes between sprayi.ng and harvesting of tomatoes. The results indicated that vegetables grown for the leaf crop should ,t’ require a larger period ._~As for pzofenofos , there were no tolerance limit and up to the 15th day after spraying residues wer~~ still detectable, accordingly, this’ isecticide can not be recommended until the time required for the comp1et disappearance of residue was established. (85) SUMMARY Tomatoes grown for either surnrrier or winter crop was sprayed with three organophosphorus insecticides; rnalathion, prrirniphos rnethyl and profenofos, all the three insecticides being recollllllended against sap sucking insects on tornatoos. Insecticides were used at the rates of 570 g-va-u. rnalathion, 750 g-s-a.r. prrirniphos rnethyl and 540 g.a.i. profenofos per feddan, all the insecticides used were In cornrrierc.ial emu.lsifiable concentrate fOTlllulations~ Three rnethods of exraction were tried out and one of them was selected by vertue of its reproduceability and being less cOlllplicated~ Residues were cleaned up and determiried by gas chromatography for deposits on both fruits and Ieaves-> Results indicated the following: 1- The largest initial deposit was that of pIT1111Iphos rnethyl, indicative of the relat.ionship between concentration and initial d4: !posit. When rna.lathiori and profenofos were cOJnpared, however, less deposit of profenofos was found, the difference was not proportional to the srnall difference of rate of application, thus pointing to forrrrulation the probability constituents. of the of (86J 2- In all cases leaves retained more deposits than frutis indicating the effect of weight to surface ratio effect on initial deposit in addition to the effect of the texture of the sprayed surf4ce~ 3- Residues of pirimiphos methyl were the least persistent of the three insecticides investigated, followed by malathion with a rather small difference, while profenofos was conspicuously more persistent than the other two insecticides and this observation W,lS true for both leaves and fruits. 4- In malathion and pirimiphos methyl the deterioration of residues was slightly slower on the winter crop compared to the summer crop nlthough the diference was rather small in mnlathion and slightly more pronounced in pirimiphos methyl;; In profenofos, however, the deterioration rates and pattern were alaost identical in both seasons. 5- The rate of residues decomposition was always faster on and in tomato fruits compared to leaves. This was explained by the fact that initial deposit vas larger on leaves compared to fruits in addition to the difference in (87) texture and its probable effect on the binding nature of the insecticide to them. 6- The tolerance limit for malathion on and in tomatoes is 3 ppm and for pirimiphos methyl is 1 ppm. Residue determination indicated that both limit were surpassed after 12 days in both summer and winter crops, so this period can recommended to slopes between sprayi .ng and harvesting of tomatoes. The results indicated that vegetables grown for the leaf crop should ,I’ require a larger period. ~As for pzofenofos, there were no tolerance limit and up to the 15th day after spraying residues wer~~ still detectable, accordingly, this’ isecticide can not be recommended until the time required for the comp1et disappearance of residue was established. |