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.

Autumn activity and hot spots

The 2020/21 fruit season has been a particularly bad year for Queensland fruit fly. Numbers of fruit fly trapped in urban areas of the Goulburn Murray Valley (GMV) are on their way down but are increasing in peri-urban and rural areas. The likely cause of this cross-over is that urban fruit are nearly finished and large volumes of commercial or larger-scale crops are now ripe in peri-urban and rural areas, attracting Queensland fruit fly from urban areas, through peri-urban locations and into commercial crops.

Cobram urban and Cobram rural are showing low numbers now, when in previous years they registered higher numbers. It is likely that the sterile insect technique pilot trial, now in its second year in Cobram, has had a significant beneficial impact.

Other locations are proving much more difficult to reduce Queensland fruit fly. These are referred to as ‘hot spots’ and are being targeted as a result of the GMV’s Area-Wide Management strategy. Hot spots currently identified on the Goulburn Murray Valley Queensland fruit fly trapping grid are located in:

  • Merrigum
  • Nagambie
  • Katamatite
  • Katunga
  • Numurkah
  • Euroa
  • Ardmona

Conditions favourable for fruit fly survival and spread

Favourable weather conditions, due to the La Niña weather pattern present in South Eastern Australia since March 2020, has provided ideal conditions for the survival and spread of Queensland fruit fly. La Niña is still present but weakening and is expected to be neutral by mid-autumn.

Despite the positive efforts of communities in keeping fruit fly numbers down within the Goulburn Murray Valley, the impacts of favourable weather conditions have resulted in a population increase. There is no doubt the situation would have been worse without the work of these communities. Continued vigilance is more important than ever.

Ideal weather conditions expected to continue

The Bureau of Meteorology forecasts indicate there is a 55-65% chance that April rainfall will be higher than average (25-50mm for April) and a 60-65% chance that rainfall during the three months from April through June will be higher than average (50-200mm for these three months).

Forecast maximum temperatures are only a 35-40% chance of being higher than the average for April 2021 (21-24˚C). Weather forecasts show there is likely to be little change in maximum temperatures (average range is 18-21˚C) in the GMV region over the three months of April through June.

On the other hand, minimum temperatures are likely (60-70% chance) to increase over the average for April (6-9˚C). The three-month outlook, April to June, also shows a good chance (65-70%) that minimum temperatures will be higher than the average range (3- 9˚C).

Rainfall and minimum temperatures through April that are higher than average are expected to promote the extension of the current Queensland fruit fly damage season and survival in the coming winter. Maximum temperatures, at this time of year, have little impact on Queensland fruit fly.

Help stop the spread

More fruit fly on the landscape means any fruit that is around will be infested. Seemingly insignificant fruit such as the odd roadside feral peach, or a bank of prickly pears, will be heavily attacked and become the source of large new populations.

It is essential to clean up and destroy as many fruit fly host fruit as possible. Community members and growers are asked to be on the lookout for feral fruiting plants, untended fruit in abandoned orchards, vacant ground, creek banks, roadsides and rental properties, as well as front, side and back yards. Even small numbers of fruiting plants will be targeted by Queensland fruit fly under La Niña weather conditions.

Unmanaged fruit must be controlled through autumn, as it is the root cause of fruit fly population explosions in spring. Fruit fly are desperate to find fruit to lay the last of their season’s eggs into in April before they switch to winter survival mode (seeking protein, sugar and shelter). Young Queensland fruit fly reared on these fruit will emerge as adults in late April/ early May and look for food and shelter to survive winter.

If all susceptible fruit could be removed from the landscape at this time, there would be little chance of fruit fly surviving the winter in great numbers.

Post-harvest hygiene essential

The shortage of labour to pick fruit this season has caused many growers to leave

excess fruit on their trees or the ground. Although growers are not responsible for this labour shortage, unmanaged fruit is a potential food source and breeding habitat for fruit fly.

Post-harvest hygiene is essential to suppress current populations and prevent increased fruit fly pressure occurring and impacting next season’s harvest.

Post-harvest hygiene tasks include:

  • Slash or mulch.
  • Rake out from under trees and slash or mulch.
  • Cover with impermeable sheeting and fumigate with chemical approved for this purpose.
  • Deep bury – cover must be more than 30cm deep and be packed down (clay soils are generally not suitable due to deep cracking if they dry out).
  • Apply approved sprays as per your advice from your agronomist.
  • Feed to animals, run stock to clean up orchard floor.
  • Burn (use of accelerant may need approval).

Home gardeners onboard

Home gardeners and property owners can help in the fight against fruit fly by undertaking a few simple actions to help prevent and control the spread of fruit fly.

Essential strategies for home gardeners with a fruit tree or vegetable patch include:

  • Monitoring through trapping.
  • Regular inspection of fruit.
  • Use of baits and netting.
  • Pick fruit early or as it ripens.
  • Fruit and tree removal and destruction.
  • Let your neighbours know if there is a fruit fly build-up.

Key autumn tasks for home gardeners include:

  • Remove fruiting plant.
  • Remove fruit and cook, eat, process.
  • Remove and destroy fruit (solarise, heat, freeze, burn, drown) – don’t compost.
  • Net trees, single tree, branch or individual trusses or fruit.