[Remarks on the chemical control of citrus Parlatoria pergandii Comstock and Lepidosaphes beckii; side effects]
1996
Rodriguez Reina, J.M.
In order to evaluate the efficacy of several pesticides on the species of diaspidid scales, six field trials were carried out between 1990 and 1994. The chemicals tested were eight organophosphates, three insect growth regulators, mineral oil at different rates, and mixtures of some of those chemicals with oil. Four trials were done at the first maximum of inmatures (June), one at the second (August) and one at the third (November). The efficacies were evaluated observing the insects on fruits at harvest. When evaluating the efficacy of the chemicals as percent of fruits occupied by more than 10 scales, chlorpyrifos and pyriproxyfen, either alone or mixed with oil, and mineral oil at 2 per cent, were the best on L. beckii, with efficacies above 85 per cent. Those same chemicals and chlorphenvinfos, methidation and quinalfos are the best on P. pergandii, with efficacies above 80 per cent. In two trials, the efficacies on L. beckii on fruits at harvest were compared with efficacies on leaves after the sprays, observing poor correlations between both procedures of evaluation. The evolution of different developing stages of the two diaspidids was studied all along the year, between 1992 and 1995, in order to develop a predictive model for the moment of spraying based on accumulated degree days. The thermic constant estimated for completing a generation of L. beckii was 1,035 degree-days above a threshold of 8 degrees C, while for P. pergandii 815 degree-days were needed above a threshold of 11.5 degrees C. More accurate predictions are obtained for the moment of maximum of inmatures when considering the physiological time (degree-days accumulated from the 1st of January) than when considering the calendar time (date).
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