Queensland Fruit Fly Outlook for May 2019

This information has been commissioned by the Goulburn Murray Valley Regional Fruit

Fly Project and is funded by the Victorian Government’s Managing Fruit Fly Regional Grants Program. Use of this material in its complete and original format, acknowledging its source, is permitted, however, any unauthorised alterations to the text or content is not permitted.

Fruit fly situation – April 2019

During the first two weeks of April 2019, a total of 389 flies were trapped in the 375 traps deployed in the Goulburn Murray Valley (GMV) giving an average of 1.03 flies per trap per week (FTW). There were 253 flies (1.00 FTW) found in rural trap sites (252 sites) and 136 flies (1.08 FTW) in urban sites (125 sites). Normally, trap capture rates are higher in urban areas than in rural areas. However, as forecast last month, rural rates are catching up with urban rates as more and more fruit become attractive to Queensland fruit fly (QFF) in rural areas. Rural trapping rates are now on the increase as QFF move from urban areas, where fruit fly host material is now relatively limited into rural sites where a large volume of fruit fly host material is currently ripening. Urban FTW peak in late September usually and then again over an extended period from mid-December to late January. Rural FTW, on the other hand, tend to peak over the period from mid-March to early May.

Figure 1 shows the trends for urban and rural QFF trap captures as flies per trap per week (or fortnight) during the entire GMV project duration to date (15 April 2019). Figure 2 shows the same data with data for rural and urban traps pooled giving a graph of the total rate of

QFF/trap/assessment. The difference between trap capture rates between rural and urban trapping sites is evident throughout most of the project.

The other noticeable trend is the decrease in trapped QFF for the mid-March to mid-April period of 2019 (yellow box in Figure 1 and Figure 2) compared with the same period of 2018 (blue box). This difference is most likely to be due to a combination of the effects of the hot, dry summer of 2019 and the community based area wide management activities currently underway.

Figure 1. Data from the GMV Fruit Fly Project trapping grid from commencement (May 2017) to present date (15 April 2019) RURAL TRAP RATES and URBAN TRAP RATES

Figure 2. Data from the GMV Fruit Fly Project trapping grid from commencement (May 2017) to present date (15 April 2019) – QFF TRAPPED PER TRAP PER ASSESSMENT (week or fortnight)

Queensland fruit fly hot spots for March 2019

If your commercial orchard is close to any of the following urban areas which are, at present, registering high QFF populations, you should be ready to commence QFF control programs (if you haven’t already done so).

  • Ardmona
  • Cobram
  • Echuca
  • Grahamvale
  • Kyabram
  • Merrigum

QFF population patterns for 2017 and 2018 saw QFF become and a problem in rural areas from mid to late-January. This did not occur in 2019, possibly due to a significantly hot and dry summer. However, with the advent of cooler days during early autumn the number of fruit flies are now increasing in rural areas and decreasing in urban areas. This is the normal pattern but delayed a few weeks due to the adverse impacts of the weather on QFF. This indicates that the hot, dry summer and community based area-wide programs have, in fact, killed out a large proportion of the QFF population.

It is highly recommended to ensure that your traps are fresh (following label instructions) and placed in suitable locations to intercept QFF coming into your orchard. It is also highly recommended to commence, if not already done, a bait-application program. This is especially important if you or your neighbours experienced fruit fly problems last season.

Table 1 shows all locations within the GMV where there were significant increases in the numbers of QFF trapped. These sites should be regarded as likely hot spots.

Table 1. Flare ups within the trapped area of the GMV in the first two weeks of April 2019

Weather outlook

Data from the Bureau of Meteorology forecast that chances of rainfall for May 2019 being above the average of 10-25mm are not likely (a 40-45% chance for the GMV). QFF would find these levels of rain to be extremely limiting but, with irrigation and urban garden watering they should survive, in areas serviced this way, without difficulty.

Maximum temperatures, for the same period, are likely (70-75% chance) to be higher than the average of 15-18˚C. Minimum temperatures are, also, likely (65-70% chance) to be higher than the average of 3-6˚C.

Temperatures that are warmer than normal will favour QFF population build up, but this will probably be reversed due to the likely lack of rainfall. However, this adverse impact on QFF due to lower rainfall is unlikely to occur in home gardens in urban areas. This is due to the use of home gardening watering systems and home heating which artificially raise localised relative humidity and temperatures (close to the house) and improves the survival of QFF eggs, larvae, pupae and adults at that site.

Figures 3 to 5 show data extracted from the Bureau of Meteorology outlooks for May 2019 outlooks for the chance that maximum temperatures, minimum temperatures and rainfall, respectively, will exceed average March weather conditions.

Figure 3. Likelihood that May 2019 maximum temperatures will exceed average March levels (1990 to 2012).

Figure 4. Likelihood that May 2019 minimum temperatures will exceed average May levels (1990 to 2012).

Figure 5. Likelihood that May 2019 rainfall will exceed average May levels (1990 to 2012).