Abstract

In May, 1988, trials were Initiated to determine optimum critical levels for control of Empoasca spp, based on percentage of nymph Infested leaves. The efficiency of this sampling comparing It to absolute values obtained from Insect traps was also evaluated. A randomized complete block design was employed at two locations with three replications and five treatments per location. Insecticides were applied when leaves had infestation percentages of 0, 15, 30 and 45 %. An added check was also included without insecticide applications. To each treatment, “dimetoato” was applied to determine the critical level. Plot sizes were 49 in’ while harvest areas were 4 m2 taken from the center of each plot. The combined analysis of variance Indicated significant differences between yield amongst the applied treatments (P<0.01). Yield increases of 0 and 5% (1.1 and 1.2 t ha-1, respectively) were significantly higher than the check (0.8 t/ha) for treatments 30 and 45% defined above. The correlation between porcentage of infested leaves and number of nymphs determined from the traps was significant (r = 0.78) at Corral Falso and (r = 0.56) at San Jeronimo. The treatment with 15 % infested leaves provided the largest net benefits. The marginal rate of return for this critical level was 5 and 20% for San Jeronimo and Corral Falso respectively.