Efficacy and phytotoxicity of multiple petroleum oil sprays on sweet orange (Citrus sinensis (L.)) and pummelo (C-grandis (L.)) in Southern China

The efficacy of pest control of three different oil formulations in multipl e low-concentration spray programmes on sweet orange and pummelo were compa red with unsprayed and normal farmer-treatments over three years. Phytotoxi city of sprays was assessed in terms of fruit and leaf drop, fruit yield an d external fruit quality. Trees sprayed with any type of oil had lower pest numbers than unsprayed trees. On sweet orange, the heaviest oil was better than the normal farm practice at controlling chaff scale on fruit and red mite and whitefly on leaves. On pummelo it provided the best control of red mite on leaves. All three oils were as effective as the normal farm practi ce in control of rust mite on sweet orange fruit and leaves and red mite, r ust mite and red scale on pummelo fruit. On sweet orange trees there was no evidence of phytotoxicity, and the external quality of fruit generally imp roved over time. On pummelo trees, oil sprays were unable to improve the ex ternal fruit quality. The number of pummelo per tree was reduced in three o f the oil spray schedules in 1995 and one in 1996, but the total weight of fruit harvested per tree was unaffected.