*Bronwyn Koll

I expect we are in for another high-pressure fruit fly season (2022–2023) given several factors.

There were still Queensland Fruit Fly (QFF) populations present last autumn; the likely La Niña and negative Indian Ocean Dipole (IOD) influence over rainfall and humidity this season; favourable QFF weather days already occurring in August (temperature); and some QFF detections already recorded in August 2022).

This means QFF can’t be ‘ignored’ or ‘addressed later’, and we will all need to use all the tools in the toolbox this season.

QFF pressure late autumn 2022

Queensland Fruit Fly pressure remained high the end of last fruit season. Janren Consulting’s report for the GMV fruit fly program, ‘Queensland Fruit Fly Goulburn Murray Valley Grower Outlook May-June 2022’, suggests “weather conditions for April and May 2022 were not significantly damaging to fruit fly survival and activity, indicating the fruit fly season will extend further into late autumn and early winter than usual.”

The Yarra Valley also experienced QFF activity in May 2022. I’ve just received the report of a single QFF found in the Yarra Valley last season (May 2022) stating: “Qfly, female, ovaries developed with few well-formed eggs … most likely not mated yet… with a larger number (of sample flies to test) we could (potentially) argue for an overwintering population of adults that will mate when the new favourable season starts.”

Unless there were concerted efforts to treat potentially QFF damaged fruit fallen to the ground, and unless there were effective baiting and chemical controls still being applied late in the 2022 fruit season, the experts have indicated we can expect carried over QFF pressure for this spring and into the 2022–23 fruit season.

Rainfall and humidity

On the back of two La Niña influenced fruit growing seasons where Queensland Fruit Fly populations were aided in survival by higher-than-average rainfall and humidity, we are quite possibly in for another wetter than average season ahead that will most likely promote QFF survival and increase QFF populations, therefore pose an increased QFF risk to fruit production.

According to an ABC News article (3 August 2022) ‘BOM declares negative Indian Ocean Dipole, likely to add to unrelenting rain in Australia's east’ the Bureau of Meteorology are giving indications of the formation of another La Niña and suggesting the likelihood of rainfall and humidity will also be increased due to the influence of the negative IOD climate driver.

Warm August days and QFF activity

The spring weather has already graced most of Victoria, albeit for a brief period. Janren Consulting shared some recent temperature observations with our team of QFF Area Wide Management (AWM) co-ordinators about a significant warming trend of day and overnight temperatures in all Victorian regions for the first week in August. During this same week, early reports are suggesting a small number of QFF detections in monitored QFF traps in the Goulburn Valley.

Interpreting conditions and using clues to improve QFF control

It is important to remember the role of the QFF monitoring traps in this seasonal outlook work, and how the information can support early action in any region (high or low QFF pressure).

QFF monitoring traps only attract mature male fruit flies

The information about QFF population detections is based on findings in the network of QFF male-attracting traps. The lures attract males that are reaching maturity and a ready to mate. We know that this means the male QFF have been feeding and maturing for a period of time leading up to the point that they are lured to the trap.

The opportunity to use a food-based bait to control these very flies existed over the prior fortnight period leading up to his capture, (where the male QFF was spending his time feeding). We also know that the presence of male flies is a strong indicator of female flies in the area.

QFF baiting needs to start now

QFF don’t travel far unaided, and this is where I believe we can get the early jump on controlling the QFF population. If baiting activities started in early spring (in selected areas), QFF populations would potentially never increase exponentially like they have the capacity to do uncontrolled. Best to try and be ahead of the QFF population curve!

QFF control would be best utilised at targeted sites in early spring in these situations:

- Historical risk

Where QFF was known to be present at the end of last autumn – including habitat near apple blocks

- Evidence risk

Where QFF are being detected in traps now – see your own property trapping data

- High risk practices

Where high-risk practices are currently occurring (i.e. fruit production such as citrus hanging on trees, or other unprotected and unharvested fruit hosts) – look around your farm and help your neighbour or roadside area deal with overwintering produce that could be hosting QFF

- High risk habitat

Where QFF habitat has hosted flies overwinter such as warm, protected areas (bush areas, stored timber, shrubs around dams and creeks, sheds, chook houses, and evergreen trees, especially home gardens).

Advantages of early baiting

Bait can be applied in high-risk locations on the warmer days, at times when QFF are most likely going to be out feeding (before mating). This need not be regularly each week until the weather or trapping data indicates regular QFF activity.

A stitch in time saves nine! Chemical volume could be kept to a minimum, and target areas could be exploited with effective baiting to prevent the need to cover a wider area with QFF controls later.

If channel water supply for bait application is an issue, consider how to apply a concentrate bait formula that uses less water, and apply it in key areas. (See your agronomist for best rates for your use and to check your equipment – it may need to be calibrated, altered or new equipment made).

Tips going into spring:

- Set up your traps as early as possible with fresh lures – write the date on some traps as a visual reminder for when to refresh the lure inside. It’s really important to refresh lures by the use-by date as the active kill agent expires, becoming ineffective

- If you haven’t already, task a person/service with regular trap checking to get accurate data firsthand, and in a timely manner to be able to action a corrective response ASAP

- Use QFF protein-based traps as well as QFF male attracting traps (set them up separately) to survey the whole QFF population and gauge activity of both male and female QFF

- Apply bait early in strategic locations to get ahead of the predicted curve that this season could see occur

- Work with your neighbours to discuss good area wide management of QFF – it will only work if we are all doing it together and taking this fight seriously.

*Bronwyn Koll, is the Yarra Valley coordinator for the Queensland Fruit Fly Prevention and Management project, funded by Agriculture Victoria and managed by Agribusiness Yarra Valley. The region acknowledges the risk of the QFF incursions and the threat to local fruit production and has valued the early detection and rapid response tools used community wide. The project promotes the area wide management approach, meaning everyone has to be involved and do their bit. Contact: qff@agribusiness-yarravalley.com