Selective use of insecticides for control of armored scale (Homoptera: Diaspididae) in San Joaquin Valley California citrus

A citrus orchard infested with organophosphate-susceptible California red scale, Aonidiella aurantii (Maskell), was given augmentative releases of the scale parasitoid Aphytis melinus DeBach, and groups of trees were sprayed with narrow-range 415 spray oil at 3 different times of the year, an early season application of the organophosphate chlorpyrifos, or 2 applications of the insect growth regulator buprofezin, to determine if these insecticides could be combined with natural enemies to control the scale. Narrow-range oil was not efficacious against A. aurantii when applied to 3rd-instar scale in March and was only moderately effective when applied to high densities of 1st- and 2nd-generation crawlers in May and July, respectively. In addition to only moderate efficacy, the May application of narrow-range oil reduced densities of predaceous mites, increased citrus thrips fruit scarring, and reduced yield. Chlolpyrifos and buprofezin both were more efficacious than narrow-range oil. However, chlorpyrifos reduced densities of Euseius tularensis (Congdon) needed for citrus thrips control and reduced densities of A. melinus and Comperiella bifasciata (Howard) needed for scale control. Buprofezin was efficacious, selective and nonphytotoxic, however, it is not yet registered for use. In a 2nd experiment where A. melinus were released, chlorpyrifos and oil in 2 volumes of water were applied to trees infested with organophosphate-resistant yellow scale, Aonidiella citrina (Coquillett). In this situation, chlorpyrifos was ineffective in reducing scale and at the end of the season, the chlorpyrifos-treated trees had substantially more scale-infested fruit than the untreated trees. In this low density yellow scale situation, the narrow-range oils were not needed for control as oil treatments resulted in similar densities of scale compared with the untreated trees