VARIABILIDAD ASOCIADA A LA DETERMINACIóN DE RESIDUOS DE CLORPIRIFOS AL SER APLICADO EN UN HUERTO DE MANZANOS

the present study had the purpose of testing through supervised trials the variability of chlorpyrifos (chp) residues associated to a sampling methodology validated in the field, on applying the active ingredient (ai) in an apple orchard, with two different spraying methodologies and at different periods of vegetative development. the persistence on applying 1.8 kg ha-1 (lorsban 50%wp？, dow agroscience, usa), using a knapsack sprayer with engine (kse) and a high volume sprayer (hvs) was studied. the model that had the best fit for the diminution of the residues was appraised through linear regression. the results show high coefficients of variation (cv) with both application methods, kse (69%) and hvs (43%). the sampling variability of apples contributes to 99.3% with kse and 97.7% with hvs. the sample results show an initial rapid diminution of chp, with a half-life for apples, leaves and soil of 5.0, 2.3 and 4.5 days for kse and 8.3, 2.7 and 11.2 days for hvs, respectively. the adjusted declination model for each substrate does not permit modeling the degradation of chp residues through a simple model.