Queensland Fruit Fly Outlook – November 2021

This information has been commissioned by the Goulburn Murray Valley (GMV) 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 unauthorised alterations to the text or content is not permitted.

October review

• Cobram data for 2020 and 2021 has been excluded from this report as the separation of numbers of wild flies from sterile flies (part of the SITplus sterile pilot insect technique project (SIT) in Cobram, 2019 – 2021) has not been completed.
  • About 2 million sterile Queensland fruit fly (Qfly) were released by air over a selected area of Cobram per week from early to mid-September to April each year from 2019/20 to 2021/22. Sterile fruit fly trapped in the Goulburn Murray Valley (GMV) fruit fly trapping grid are separated from wild flies to assess the efficacy of the SIT project.
  • In 2019, with sterile/wild separation, during this period there were 12.7% wild fruit fly. It is likely that the same proportion would exist in 2021.
• Fruit fly populations, as measured by the GMV trapping grid, are showing the usual pattern for this time of year (FIG. 1).
  • Fruit fly populations are in the middle of the spring peak. These flies are considered to be overwintering adults leaving their winter refuges in search of mates and fruit to infest.
• Trapped fruit fly numbers from September to mid-October 2021, with Cobram data excluded, were lower than those in the same period over the history of the Goulburn Murray Valley Area Wide Management project since it was established in 2017.

NOTE: When sterile and wild fruit fly are separated the actual numbers will be known.

• If 12.7% of trapped fruit fly are wild as they were in 2019, it is likely that the figures for both 2020 and 2021 will increase by about 150 fruit fly. If these estimated wild fruit fly from Cobram are added to the total the result is that 2021 is still lower than all other years except 2018.
• When individual fortnight data are examined (FIG. 3) it appears that data for October 2021 may still be on its way up due to a delayed fruit fly spring build-up. This won’t be verified until data from ate October are received.

• Also, as usual for this time of year the greatest numbers of trapped fruit occur in urban areas (FIG. 3), where winter temperatures are higher than rural locations (heat sink effect) and the diversity of fruiting plants available of infesting is also higher in urban areas.
• Weather data for September/ October 2021 (TABLE 1) show that some areas within the Goulburn Murray Valley are more susceptible to post-winter proliferation than others. For example, Cobram, Yarroweyah and Strathmerton had 12 days where sunset temperatures were over 15˚C (the time and minimum temperature at which fruit fly mate) while Mangalore and Avenel had only 6 days. This means that trapping numbers may be higher in October/ November in the former sites but won’t peak in the latter sites until later on in the season (November/ December).
  • Minimum and maximum temperatures were not limiting to fruit fly survival at this time.

Hotspots

• There are 14 sites in Cobram (13 in urban locations and 1 in a rural spot) which trapped 8 or more fruit fly in the 6-week period from 1 September 2021. However, it is likely that most of these flies will soon be identified as sterile and not wild.
• Other locations with 8 or more wild flies in total per trapping site were:
  • Kyabram – 1 site
  • Orrvale – 1 site
  • Mooroopna – 2 sites
  • Shepparton – 6 sites

November outlook

• Numbers of trapped fruit fly will decline either in late October or through November (FIG. 1).
  • This reflects the dying out of overwintered adults.
  • Many of these adults would have mated and laid eggs.
  • The first new season generation of fruit fly will emerge from eggs laid by these overwintered fruit fly. The size of this population will impact on subsequent damage to crops in urban and rural areas of the GMV from about Christmas 2021 onwards.
  • Fruit fly numbers will recommence increasing in late December and will continue this increase throughout January to April with a small decline during January when very hot, dry weather occurs.

Advice for home gardeners:

• Remove unwanted fruiting plants
• Harvest fruit and use or destroy them
• Place traps out and check regularly for sign of fruit fly population build-up
• Check ripening fruit for sting marks or maggots
• Netting whole plants, fruiting branches, fruit trusses or individual fruit is a sure-fire way of protecting your crops from fruit fly.
• Baiting is not recommended for backyard growers unless everyone in the area start baiting, and continue it, together
• Don’t restrict your vigilance to your backyard – fruit fly can be in fruit in your front yard, nearby vacant land, untended crops, roadsides and creek banks
• Fruit fly will build up over November onwards in urban areas
• Fruit fly will spread from urban areas to rural areas as commercial orchards start to ripen – generally from March onwards
  • Fruit fly management in urban areas early in the season will assist in reducing fruit fly impact on commercial growers later in the season.

Advice for peri-urban landowners

• Fruit fly is in low numbers in your areas right now
• Use traps and check fruits for stings and larvae now so that you know when fruit fly is starting to build up
• Fruit fly move from urban sites through peri-urban areas and into commercial orchards during the late summer and autumn. Control of fruit fly in your locations will assist commercial growers in controlling fruit fly in their crops.
• Removal of fruiting plants or their fruit will help in reducing the numbers of fruit fly breeding in your area
• Baiting can be very effective in peri-urban locations if fruit fly numbers build up to damaging levels
• Consider using netting for special crops

Advice for commercial growers

• Fruit fly is not a problem in rural locations as yet but –
  • Make sure you have traps out in the orchard and surrounding the house and sheds
  • Ensure the traps, lures and toxicants are within their use-by date and replace or re-charge as per label instructions
• If your orchard is close to towns mentioned above as hotspots make sure you check your traps regularly as well as checking your crops and other fruiting plants in and around your orchard – house paddocks, front yard, roadsides, creek banks, etc.
• In more remote areas fruit fly numbers will commence building up in late summer and early autumn
• Baiting is very efficient at controlling fruit fly so ensure you have stocks in storage inside their use-by date, especially if fruit fly was present in your area last year.

Weather forecast

• Bureau of Meteorology data predict that there is a high chance (75% to 80%) that more rain will fall during November 2021 than average (which is 25mm to 50mm) (FIG. 5).
• Maximum temperatures will remain similar (40% to 45% chance of being higher than average) to the average of 24˚C to 27˚C (FIG. 6).
• The chances that minimum temperatures will be higher than average (9˚C to 12˚C) are high (65% to 75% chance) (FIG. 7).
• These conditions are favourable for fruit fly survival and population build-up.

Goulburn Murray Valley Fruit Fly Project 

For assistance in managing Qfly, contact the Project Coordinator at the GMV Fruit Fly Office by phoning (03) 5871 9222 or emailing gmvfruitfly@moira.vic.gov.au. For more information on fruit fly control and area wide management strategies visit www.fruitflycontrol.com.au

This report was produced by Andrew Jessup, Janren Consulting Pty Ltd in conjunction with analysis of regional trapping data supplied by the GMV Fruit Fly Area Wide Management Project.