IK Caldwell, with funding from the State Government of Victoria and Horticulture Innovation Australia, has deployed over 300 male-targeting Queensland Fruit Fly (QFF) traps in and around 21 towns between Strathbogie, Victoria and Barooga, New South Wales. Traps have been set in rural and urban areas and are checked weekly. Each trap contains a male QFF attractant (cuelure) and a pesticide (malathion).
These traps do not attract female fruit fly but are used mainly to detect the presence of QFF populations and to gauge changes in populations over time. The trapping program is a component of a larger project aimed at reducing QFF populations in the Goulburn Murray Valley region of Victoria through coordinated area wide management.
Information for home gardeners
The weather over recent weeks has been ideal for fruit flies to survive, mature and mate. Home gardeners are warned that overwintering adults, which have now died out, have laid eggs into existing fruit within the Goulburn Murray Valley (GMV) and QFF now exists as eggs and larvae in fruit and pupae in the soil. If not monitored carefully and, if necessary, controlled, these immature flies will emerge sometime in December 2017 and have the potential to cause large QFF outbreaks.
It is recommended that householders deploy male- and female-targeting fruit fly traps. Householders should take advantage of unwanted tree removal offers and consider future fruit fly control methods such as home garden hygiene, fruit bagging, tree netting and fruit fly baiting. They should also consult with friends and neighbours to help determine whether fruit flies are nearby.
Vigilance is essential as there may be a hidden fruit fly population present as immature life stages in infested fruit. If these fruit, or their parent plants, can be found and disposed of adequately then these immature stages will not result in an upsurge of populations.
Information for farmers and growers
Temperatures during October and November were suitable in all parts of the Goulburn Murray Valley for QFF maturation, mating and egg-laying.
If successful control has not been achieved then QFF may exist as eggs and larvae in fruit and pupae in the soil. If not monitored carefully and controlled, these immature flies will emerge sometime in December 2017 and have the potential to cause large QFF outbreaks.
It is suggested that owners and operators of orchards that are close to the peri-urban areas of large towns (where fruit fly numbers have increased) should prepare strategies for boundary protection against fruit flies entering their crops from the town.
It is wise for growers and farmers with fruit trees to plan future fruit fly control programs. Keep in mind that fruit trees planted in house paddocks are also very susceptible to fruit fly infestations which often go unnoticed and, therefore, untreated.
Farmers on the peri-urban fringe of large urban areas which have a history of fruit fly problems should deploy fruit fly traps and keep an eye on ripening fruit for fruit fly sting marks.
Farmers should remove unwanted fruit fly host plants in their house paddock, along creek banks, on roadsides near their farm and other areas. If their farm had fruit fly problems last season they should consider future fruit fly control methods such as orchard hygiene and fruit fly baiting, placement of more traps for more accurate detection of fruit fly population incursions and purchase of approved pesticides and fruit fly baits.
Effects of recent rain on QFF survival and proliferation
It should be noted that recent heavy rains in the region will not adversely impact QFF.
The recent weather conditions will affect fruit fly populations in the following ways:
Eggs and larvae in fruit on the tree will survive better with rain than when dry as weather is cooler and more humid so damage via desiccation is reduced;
Eggs and larvae in fruit that’s lying on the ground will survive better in cooler weather as exposure to the sun (if exposed) will not be hot enough to heat the fruit to an insecticidal level;
Pupae in the ground is very unlikely to be damaged by heavy rain (complete submersion by floodwaters would need to be continuous over more than three to five days);
Rain sometimes stimulates QFF adults to emerge from pupae in the ground as it means cooler temperatures and higher humidity for the new, soft adults;
Overall higher humidity due to cooler and rainy weather allows for easier survival for QFF;
If there is ripening to ripe fruit around right now and there are adult flies there will be an increase in flies stinging these fruit and the number of flies trapped (and therefore in fruit) will increase within about four to six weeks from now;
If fruit fly baiting is being carried out it will not be fully effective unless it is re-baited as soon after rain as possible – i.e. after each rain event;
Constant rain will help reduce the spread of adult fruit flies from orchard to orchard as flight is restricted. However, adults may still fly from tree to tree within the orchard.