Red scale spray timing prediction tool - 2016 12

Dr Jianhua Mo, December 2016

A yellow pheromone trap in a treeRed scale has multiple generations every year, which can mean costly, repetitive spray programs. Knowing the most appropriate time to spray – when crawlers and whitecaps are most abundant – could slow chemical resistance and improve control.

Most lifecycle stages of red scale cannot move, however, the adult males have a pair of wings and can fly. Upon emergence, they seek out the virgin females to mate, using the female sex pheromone to guide them.

Using pheromone traps to time these peak male flights can help guide red scale control. Crawlers and newly settled first instars (whitecaps) are the most vulnerable lifecycle stages of red scale to insecticide sprays, including petroleum spray oils (PSO). The peak crawler abundance occurs several weeks after the peak male flight – temperature (degree days) is used to predict this peak and spray timing.

Allowing scales to develop into later stages (i.e. mid to late December) makes them more resistant to oil or other contact chemical sprays and thereby reduces the effectiveness of control. There have been reports of oil sprays occasionally providing poor results and, apart from oil quality, spray volume and application issues, timing could have been an influencing factor.

In practice, most growers spray oil for various scale insects in December. Based on overseas data, the time to spray could range from three to five weeks after the first peak red scale flight and, in a normal season, the oil spraying time might be around late October to mid November in the southern growing regions of Australia.

This Horticulture Innovation Australia project will adapt the USA data to Sunraysia and Riverina conditions so a more accurate and regional red scale spray timing tool can be developed to provide better control of red scale.

A line graph showing red scale flights

During 2015–2016, NSW DPI monitored seasonal patterns of red scale male flights in the in the Riverina and Sunraysia with pheromone traps (Figure 1). Data from the Riverina showed 2–4 peaks of male flights during October 2015 and March 2016 (Figure 2). At all three monitoring sites, the first peak appeared in early October and the second in early December. The early October peak was relatively narrow, with the numbers dropping quickly after peaking. The early December peak was similarly narrow at one site, but quite broad at the other two sites lasting several weeks. A third male flight peak was also noticed around early February at two sites.

Contact: email Dr Jianhua Mo or telephone 02 6961 2537.