Red scale control investigations on citrus in Queensland, 1951-1958

Between 1951 and 1958 seasonal history observations and 12 field control trials were carried through on citrus in Queensland, mainly in the Gayndah district, on red scale (Aonidiella aurantii (Mask.)). Observations confirmed earlier work indicating that five generations and a partial sixth occurred each year. While these may overlap, distinct brood emergences were observed in October, December and May. The earlier field trials investigated timing, concentration and combination of white oil and parathion sprays, and two formulations of parathion. The most effective treatment for scale control was found to be white oil at a concentration of 1 in 60 used twice in early December with a 2-week interval, followed by a 1 in 40 white oil spray in late January. The follow-up spray was best used in early April for Late Valencia orange. Glen Retreat mandarins required a lower oil dosage to avoid fruit injury, but control was easier in mandarins due to natural throwing of scale from the rind. For this variety it was found that single sprays in early December and late January of 1 in 80 white oil plus 0·015 per cent. parathion emulsion were quite effective. Later field trials indicated that a paraffinic oil was equal to white oil as a scalicide and produced less damage on susceptible trees. Preliminary work on malathion showed that it had relatively low scalicidial value alone but a mixture of 1 in 80 white oil and 0 · 05 per cent. malathion gave indications of good protection. White oil did not affect time of fruit maturity. The only effect on colouring of oranges caused by oil sprays was on early varieties picked green-mature and artificially coloured. The effect was of little consequence in fruit coloured on trees and late fruit.