Determine seasonal occurrence of Bryobia in apple orchards for the development of a control strategy based on a treatment threshold

The objective of this project was to obtain a better understanding of Bryobia mite by monitoring its seasonal occurrence in apple orchards to determine the need and frequency of oil sprays and the possibility of implementing a control strategy based on a treatment threshold.  The main observation over the study period was a progressive increase in all pest mite populations.  During the 2006/07 season a rest breaking oil spray was applied to all orchards.  A total of four Bryobia adults were recorded on the leaves removed from the sampling sites on Nooitgedacht.  No Bryobia adults or immatures were observed from the orchards monitored on Rocklands or Welgemeen (Warm Bokkeveld).  During the 2007/08 season the oil spray applied for delayed foliation was not applied to the orchards monitored for Bryobia.  Although there was an increase in the number of Bryobia adults recorded on the leaves the population levels continued to remain low and adults appeared very late in the season.  The appearance of Bryobia adults and immatures appeared on the leaves and fruit at approximately the same time.  During the second season there was a noticeable increase in the number of ERM and RSM observed in all the orchards.  The most common predatory mite present was again E. addoensis.  During the 2008/09 season Nooitgedacht omitted the rest breaking oil spray for a second consecutive season while the Rocklands orchards received rest breaking oil sprays.  Although there was an increase in Bryobia population levels compared to the previous two seasons the increase was moderate.  By late January early February Bryobia eggs were observed on the fruit.  Over the study period the ERM and RSM mite populations increased to a greater extent than Bryobia.  As the study only extended over three seasons and a complete removal of oil sprays was not possible the aim of developing a treatment threshold for Bryobia could not be achieved.  However, there is little doubt rest breaking oil sprays contribute to the effective control of Bryobia.  These oil sprays also had a very effective controlling impact on ERM populations.  The study has shown that when Bryobia populations have been reduced to very low levels it is possible to reduce or leave out the rest breaking oil sprays.