SOIL SURFACE APPLICATIONS OF CHEMICALS FOR THE CONTROL OF NEONATE DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) AND THEIR EFFECT ON ANT PREDATORS

Abstract

The root weevil, Diaprepes abbreviatus, as a larva, inflicts feeding injury to the bark of all root parts of a citrus tree, thereby impairing root function and supplying infection courts for soil-borne root rot diseases. Ideally, larvae should be controlled at the soil surface before they reach the root zone. In screenhouse and field experiments conducted in central Florida from 1996-99, the synthetic pyrethroid, bifenthrin, at 0.54 g/m2 (0.554 kg ai/ha) and RPA107382, an analog of fipronil, at 0.156 and 0.312 ml/m2 (0.242-0.466 kg ai/ha), were applied uniformly to the soil surface beneath the tree to form a chemical barrier against neonates of D. abbreviatus. By comparison to the control, larval populations were reduced by 80-100% within one week and these reductions persisted for 4-8 weeks. In an open screenhouse, bifenthrin gave excellent root protection of container-grown trees during a 22 week period when neonates were added to containers weekly for 12 weeks. RPA107382 was highly effective for about 2 weeks but lacked residual effect. The accumulation of leaf litter beneath the tree impaired coverage of the soil by bifenthrin resulting in reduced control. According to weekly baited trap counts, both chemicals reduced non-target foraging ants, particularly Solenopsis invicta Buren. The reduction in S. invicta was temporary however, but it did allow time for other foraging ants to re-establish and increase.