Development of phenology models and a timing guide for the management of Californian red scale in Australian citrus (CT15008)

What was it all about?

This investment developed a timing guide for the management of red scale, a major pest of citrus crops in Australia that can infest all above ground surfaces of trees and cause fruit to be downgraded or sent for juicing.

The project ran from 2015 to 2018 and, to help citrus growers time their red scale control, it collected data on the seasonal patterns of red scale populations in the southern citrus regions, conducted chemical timing trials and ultimately developed this timing guide for peak periods of adult males and crawlers. A red scale population model was also developed to investigate the underlying mechanisms for the observed seasonal patterns.

Red scale populations are normally kept below damaging levels by their natural enemies. When interventions are needed they can involve chemical controls, including petroleum spray oils, and biological control in the form of parasitoid Aphytis wasps. However, timing is important in red scale management. Many registered chemicals for red scale control are only or mostly effective against crawlers (newborn scale nymphs) and whitecaps (newly settled crawlers) which do not have fully developed wax covers to protect them.

The project team found that individual seasonal patterns of adult males and crawlers varied considerably between monitoring sites and seasons, ranging from small, isolated peaks to broad, merged peaks. Despite these variations, the project team made the following observations:

• Red scale adult males and crawlers are more likely to peak during certain time periods. Crawlers are likely to be most abundant in November and least abundant during June to August. Adult males are likely to be most abundant in October and March and least abundant in May to August and November.
  
  
• The timing of spring male and crawler peaks can be predicted using local temperatures.
  
  
• Red scale can complete at least four generations per year in the southern citrus production regions of Australia.
  
  
• Red scale populations increase from spring to autumn.
  
  
• Aphytis wasps prefer to parasitise virgin red scale females. The timing of spring adult male peaks can be used for Aphytis releases as it is also the time when virgin females are abundant.

These observations were used to develop the timing guide tool that predicts the abundance of the red scale life stage and thereby can help growers time their control options. In general, it is recommended that red scale controls be timed at spring crawler peaks, as this will reduce the size of red scale populations in subsequent generations.

The project also found that pheromone traps are useful tools for monitoring red scale populations, though they are not widely used in Australia. They can be used to detect male flights, which in turn, can be used to predict crawler peaks and therefore timing of red scale controls. The size of trap catches provides a measure of local red scale infestation levels.

ACT NOW

• The preliminary timing guide that was created during the project is still available for download here but has since been surpassed by the final online timing guide that been developed to help growers make the predictions and time their red scale management operations
  
  
• Read a factsheet produced by the project for the 2017 Citrus Technical Forum here