Queensland Fruit Fly in July

Winter has hit the Goulburn Murray Valley and the numbers of male Queensland Fruit Flies (QFF) in traps are down to very low levels.

If there are any QFF alive in the field they will, in all probability, be adults as all eggs and larvae are likely to have died by now. There is a very, very small chance that some larvae may persist in fruit that is located in unusually warm spots on the landscape e.g. in fruiting trees near permanently heated buildings or even in the fruit bowl inside the house.

If the day warms up during this time of year, QFF adults may crawl around, or fly, in search of food, especially sugar-based nutrients from flowers and aphid honeydew as well as protein from bacteria, fungi and yeasts on plant surfaces. Food-based traps and baits are still effective, especially during warm parts of the day. Such traps and baits can control hungry fruit flies in the backyard and orchard, especially at this time of year.

Survival of these adults depends very much on the weather over the next couple of months – and a large number must survive, otherwise there will be no fruit fly problems next year (unless flies are brought in to the Goulburn Murray Valley in infested fruit from other locations).

What can you do now, in July 2018, to reduce fruit fly build-up next spring?

From now on have a close look at what plants might have fruit on them in early spring and, if you can, pull them out or at least pull their fruit off. This includes fruiting weeds, hedge plants, fruit trees with late-hanging fruit (e.g. navel oranges). If there are roadside or creek-bank rogue plants such as apricots and loquats, please let the Council know about them and ask that these plants be removed.

Likely weather patterns for July 2018 and the impact on QFF

The Bureau of Meteorology (BOM) outlooks for July 2018, based on data from 1981 to 2010 and current weather modelling, indicate:

  • An 80% chance that maximum temperatures, through July 2018, will be higher than average. Therefore, it is likely that maximum daily temperatures will exceed the average of 12˚C to 15˚C in the GMV. These temperatures are quite OK for QFF survival. That means that there will be decreased adult QFF die-off, more males entering traps in July than is normal and more adults surviving the winter into the spring.
  • A 45% to 55% chance that minimum temperatures, during July 2018, will be higher than average. So, there will probably be no change in the average range (3˚C to 6˚C daily minimum) in the GMV. This temperature range has been shown, over several years of QFF trapping in the GMV, not to impact QFF adult survival adversely.
  • A 25% to 40% chance that July 2018 rainfall will be higher than average – therefore, it is likely that there will be less rainfall than the usual 25mm to 100mm expected during July 2018 in the GMV.

What does this mean for QFF in the GMV?

Days will be warmer than normal, but nights will be as cool as usual as rain is likely to be a little less than usual. QFF adults will survive winter in the GMV but the warmer days will allow them to survive in greater numbers as long as they can return to good winter refuges, out of the cold, overnight. Adult survival will be tempered by a lack of rain and subsequent levels of relative humidity that QFF need to survive comfortably but there will be dew around in the mornings to keep adults hydrated as long their refuges are out of the wind.

It is quite possible that improved fruit fly management programs set up in and around the GMV since mid-2017, such as public awareness workshops and programs, QFF host plant removal, greater use of traps, baits and netting and the destruction of unwanted fruit may impact on QFF numbers coming into the next season. If these activities have bitten into the QFF problem and the BOM forecasts are right, we might well see a reduction in QFF in the GMV next season.

Advice to home gardeners and commercial growers

If your crop is in one of the few hot spots for QFF in the GMV, and this is evidenced by finding flies in traps in June, you can help stop flies surviving the winter and building up into damaging populations in the spring. It is these flies that then spread out into neighbouring gardens and commercial orchards.

It is still advisable to pick up fallen fruit and harvest late-hanging fruit just in case they are situated in a position that is warm enough for QFF survival. Such orchard hygiene is useful for other reasons, too, such as reduction in fungal pathogen load in the garden.

Winter trapping with protein-based traps should be placed in a spot that catches the morning sun, high in the canopy of evergreen trees, in the warmest position in the yard. Lemon trees are particularly favoured by QFF to overwinter in.

Don’t forget that the removal of unwanted QFF host plants is a very useful and effective way of controlling future fruit fly populations… and don’t forget fruiting weeds and fruiting plants growing near buildings.

Control of fruit fly for commercial orchards, in addition to trapping and baiting can be augmented with application of pesticides but these must be approved for use against fruit fly in an approved crop and region. All label requirements must be followed. Your QFF co-ordinator and rep from your local produce store can help here.

QFF outlook for July 2018

Male QFF trap numbers will stay above zero if the BOM prediction of higher than average maximum temperatures occurs. Survival of the current overwintering QFF population will not be affected by daily minimum temperatures, or with the risk of less rainfall, during July. So, the weather is unlikely to kill off the entire QFF population in the GMV. You have to help.

For assistance in managing QFF, contact the GMV Fruit Fly Coordinator, Ross Abberfield by phoning (03) 5871 9222 or emailing gmvfruitfly@moira.vic.gov.au

This report was produced by Andrew Jessup and incorporates an analysis of regional trapping data supplied by the GMV Fruit Fly Project.

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.