Queensland Fruit Fly Goulburn Murray Valley Outlook for December 2019
This information has been commissioned by the Goulburn Murray Valley (GMV) 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 unauthorised alterations to the text or content is not permitted.
CURRENT QUEENSLAND FRUIT FLY SITUATION
The new Queensland Fruit Fly (QFF) season for 2019/2020 started during the week of 21 August 2019 when traps set out around the Goulburn Murray Valley (GMV) started recording new flies. As of the week of 14 November 2019, the GMV trapping grid’s 402 traps have been visited and fly numbers inside recorded a total of 3,470 times. At the time of publication 1,270 QFF had been trapped for the season.
Since the start of the current fruit fly season, trap captures peaked during the week of 10 October 2019 with a total of 402 flies trapped. These flies were predominantly the adult male flies that survived over the winter. Their job, with the corresponding female flies, was to mate with the females who then laid their eggs into any suitably ripe fruit occurring nearby in late September, October and early November.
As of mid-November, fruit fly trap captures have fallen into a trough where relatively few flies are being trapped. This is due to the old flies that survived the winter, having died out leaving relatively few adult flies in the region. However, although this seems to be very good news it may not be the case, as during the early spring, many of the surviving adults found members of the opposite sex to mate with and many of those now-gravid females found suitable fruit to lay their eggs into. As the adults died out, they left their offspring in fruit which means the current QFF population is made up of a small number of adults and a high numbers of immatures – eggs and larvae in fruit and pupae in the soil beneath their host plants.
LIKELY FRUIT FLY TRENDS
If the fruit fly prevalence pattern in the GMV is the same this year as it has been over the past seven years, there will be an upsurge of QFF captures during the third week of November. QFF numbers will increase until the summer peak is reached, generally in late January/ early February. This peak time represents overlapping fruit fly generations and occurs while there is an abundance of fruit of many different types and species at this time of the year in urban areas.
The peaks and troughs as described above tend to occur only in urban areas and not in rural locations within the GMV. Fly numbers do not peak at the same time in rural areas. There is only a very minor spring peak, if any, in rural locations. Rural fruit fly numbers peak in midMarch/ April – when the majority of commercial fruit are being harvested.
Although it is uncertain, it seems that QFF move out of towns and into commercial production areas during the late summer. It is for this reason that so much work can be done in urban areas to control fruit flies – not only to improve production in home gardens but to reduce the spread of flies into nearby horticultural production areas.
ACTIONS TO BE CONSIDERED FOR DECEMBER
Harvesting and pruning
Right now, most fruit flies are in their immature stage in infested fruit. Some will be in the soil. You can reduce the potential number of flies prevalent in the summer, when most fruit is being harvested in urban areas, by removing and destroying all fruits, or fruiting plants, that are not wanted or, if they can be used green, or can ripen after harvest on the shelf, to harvest them early (i.e. before they can be infested).
It is recommended to prune larger trees and vines to a manageable height or size so that fruit can easily be removed. Not only will this strategy improve the quality and size of remaining fruit it will reduce the possibility that some unreachable fruit is left on the tree or vine after normal harvest. Late-hanging fruit will be the source of new fruit fly generations so need to be removed and destroyed.
If you use netting to protect trees and/ or fruit from fruit flies (as well as birds, fruit bats, etc) pruning will assist in keeping the fruiting plant within the netting, making it easier to protect. Depending on local weather conditions there may be many fruiting plants with fruit on them which could be very attractive to pest fruit flies right now.
All home gardeners as well as commercial growers who have fruiting plants in their house gardens should check these fruit as they will be potential fruit fly hosts. Even though the volumes of such fruit may be quite small in any given area they can be used by QFF as a population ‘stepping stone’ from a small number of flies to a population explosion.
We know that one QFF female may produce as many as 400 female offspring in her lifetime. We also know that one large fruit, such as a QFF-infested grapefruit, can produce many more than 50 QFF. Putting the two together means that even a few unmanaged fruit can start a huge population explosion at a later date when there are a lot more fruit around.
The following list of fruit that might be ripe in Victoria in the spring should be monitored for fruit fly infestations. It is useful to monitor for the presence of QFF by using special traps that can be obtained from your local produce store. It’s also a very good idea to check fruit manually for black sting marks and fruit tissue softening caused by QFF eggs and larvae inside.
You might even consider complete removal of these plants so that there is no chance that they are contributing to QFF survival in the GMV.
Fruiting plants that might have ripe fruit on them now:
- Berries, strawberries
- Capsicums, chillies
- Grapefruit, lemons, mandarins, lemonades, cumquats
- Gooseberries, cape gooseberries (inca berries)
- Late hanging oranges, apples, quinces, persimmons, pomegranates
Fruit fly baits for the home garden
Now that most flies are immature it won’t be long before adults emerge from their pupae in the soil in a population explosion. This new generation will cause much damage in home gardens and their offspring will then move on from urban areas to rural locations causing damage there later in the season.
Newly emerged fruit fly adults need protein to be able to mate and then lay eggs. This need for protein makes it a useful time to apply fruit fly baits because baits are based on proteins. These baits are mixed with a toxicant that kills the fly after it has been attracted to feed on the protein in the bait.
The toxicant used in the bait need not be toxic to humans. There is one toxicant that has approval for use on organic farms. The active is called Spinosad (or spinosyns). When flies feed on this bacterium-based material when it’s mixed with the fruit fly attractant (in this case, protein) the fly dies. If interested in applying fruit fly baits in your garden look on pesticide labels in your local produce store with the active ingredients: Spinosad or spinosyns. This will protect your crop as well as the environment.
Other toxicants, which need to be mixed and applied following strict label requirements, can also be used effectively and safely in the home garden and orchard. This is due to the fact that baits are used very sparingly, and they are not placed on fruit that will eventually be consumed by humans, birds and other animals. Baits are generally applied in small doses (about 100mL) to the foliage of one tree every 5 to 10m around the backyard or throughout the orchard. The protein used in the bait gives off ammonia as natural bacterial action occurs. Ammonia tends to be attractive to fruit flies but has been found to be repellent to bees and many other insects. This activity makes it an attractive fruit fly control strategy.
SUMMARY OF HOME GARDEN FRUIT FLY CONTROL STRATEGIES
The Bureau of Meteorology has forecast lower than average rainfall (10mm to 25mm) and higher than average maximum temperatures (27°C to 30°C) although no change in minimum temperatures (average of 12°C to 15°C) for December 2019. These temperatures are ideal for QFF survival, but the lack of rain may mean fewer and sparser fruiting which will reduce QFF populations. However, this is unlikely to occur if gardens and parks are irrigated.
Since the commencement of the QFF season in the GMV some of the 402 fruit fly traps deployed on the GMV trapping grid have captured significant numbers of QFF. Table 1 shows that some locations are registering high QFF trap capture rates while others show zero rates. All of the top ten highest rates occur in urban situations although two urban locations, Wunghnu and Yarroweyah, have not caught any flies at all this season.
Most of the top ten sites are also relatively newly trapped locations and so reflect the starting point for area-wide management programs in those areas.
It is also interesting to note that, with the exception of Merrigum (rural) all rural locations show low QFF incidence rates. At present there are significantly higher QFF trapping rates in urban areas than in rural sites. This is particularly noticeable when rates in the same general area are compared, e.g. Tatura urban (7.33 Qff/trap) compared with Tatura rural (0.12 Qff/trap) and Shepparton urban (7.31) cf Shepparton rural (0.33).
Goulburn Murray Valley Regional Fruit Fly Project
For assistance in managing QFF, contact the Project Coordinator at GMV Fruit Fly Office by phoning (03) 5871 9222 or emailing email@example.com
This report was produced by Andrew Jessup, Janren Consulting Pty Ltd in conjunction with the Project Coordinator and analysis of regional trapping data supplied by the GMV Fruit Fly Project.