Abstract
Three field trials with cabbage var. Market Prize were established at the Isabela Substation, AES-UPR, to evaluate the susceptibility of Plutella xylostella to various insecticides. Dosages recommended by the manufacturer were used for the first two applications in the first trial, and some double dosages were included in an attempt to get at least a 90% control of the larvae population. For the other two trials, recommended dosages and the effective higher dosages from the first trial were compared. Significant differences were obtained with methamidophos (2.34 L/ha), permethrin (0.234 and 0.468 l/ha), and fenvalerate (0.35 L/ha) for controlling the larvae. Control figures for those four treatments were 97.8, 100, 100, and 99.9%, respectively. Methamidophos, acephate, and naled controlled over 90% of the larvae only with double the recommended rates. Chlorpyrifos at 1.17 L/ha was ineffective, but at its higher rate controlled 80 to 90% of the larvae. Diazinon, methomyl, dimethoate, and endosulfan even at their highest rates were ineffective for controlling the larvae. The number of larvae increased after each application of these insecticides. The greatest numbers of marketable heads were obtained from plots treated with permethrin, fenvalerate, and methamidophos at the highest rate for each.