Soil and Diaprepes Abbreviatus Root Weevil Spatial Variability in a Poorly Drained Citrus Grove

Soil and water variability in space and time could be important for management of the citrus root weevil, Diaprepes abbreviatus (L.). We conducted a study of soil, tree, and root weevil relationships in a poorly drained grove of Hamlin orange on Swingle citrumelo rootstock (Citrus paradisi Macfad. x Poncirus trifoliata (L) Raf.). in central Florida in 2002. We hypothesized that spatial soil and water variability might influence tree health and root weevil patterns. The objectives were to assess the spatial variability of soil, water, tree health, and Diaprepes root weevil (DRW) and to determine DRW management zones based on spatial correlations. Adult weevils were monitored using Tedders traps arranged in a 34 × 25-m grid across the grove. Soil electrical conductivity (EC) was assessed using EM38, and water table, soil texture, water content, organic matter, pH, P, K, Ca, Mg, B, Zn, Mn, Fe, and Cu were measured at each trap. The weevil population peaked in June (P < 0.001), and weevil density was high in areas that were low in Mg and Ca concentrations (P < 0.05). Semivariograms, a spatial structure function, for DRW, Mg, Ca, and EC, ranged within 75 to 100 m, which matched the limits of DRW management zones delineated using DRW and EC underlying patterns. Soil EC, Mg, Ca, and Fe were correlated, and tree decline was associated with high levels of Fe and soil flooding because plants were more water stressed in flooded areas than in non-flooded areas (P < 0.01). We suggest that a management unit approach might be an option for DRW control, and that flooding events and soil Fe, Mg and Ca levels might be related to tree decline and DRW distribution patterns. (Soil Science 2004; 169:650–662)