Fruit trees such as stone fruit (apricots, cherries, peaches, plums, nectarines) can be difficult to grow free of fruit fly in areas like Perth where Medfly populations are high.
Backyard fruit can be a significant source of Medfly to commercial orchards where they occur close to each other. If you are unable to manage Medfly or do not want to harvest your fruit, consider removing unwanted trees.
Managing Medfly in the backyard video
Medfly is a declared pest under the Biosecurity and Agriculture Management Act 2007. It is mandatory to control this pest in some local government areas of Western Australia Armadale, Kalamunda, Mundaring, Serpentine-Jarrahdale and Swan.
For control to be effective, it is essential for growers (both commercial and home garden) to dispose of fly-infested or unwanted fruit, including fruit left on the tree. Fruit disposal is the responsibility of the grower. Infested fruit should be picked and all fallen fruit gathered from the ground.
Treatment or destruction methods include:
- boiling and then feeding cooked fruit to poultry or pigs
- solarising by placing fruit in plastic bags, preferably black rubbish bags so that the heat from the sun kills the eggs and larvae
- freezing for at least 24 hours
- mulching to a pulp consistency
- spraying with a registered insecticide
- placing in waterin a container with a film of kerosene or oil for at least seven days
- burial to a depth of at least 1 metre.
Two chemical control techniques, baiting, and lure and kill, are recommended. Best control is achieved if both treatments are undertaken.
You should start during the early stage of fruit development when the fruit is a third of its final size and continue until all fruit has been harvested.
Females require a source of protein to mature their eggs and to maintain egg production. They usually obtain protein from fruit juice, bacteria and bird droppings. Baiting consists of applying coarse droplets of a protein liquid, laced with insecticide, to leaves. Male and female medflies are attracted to the protein as they forage for food, feed on it, and acquire a lethal dose of insecticide. Baiting targets only medfly adults and conserves beneficial insects.
Baiting may not provide control of Medfly in crops that are highly susceptible, or in high pressure areas such as in suburbs with many established fruit trees.
Female Medflies may find ripening stone fruit more attractive than baits. Effectiveness is increased if applied over a wide area such as in a community baiting scheme – so encourage your neighbours to also bait their trees.
The organophosphate maldison is registered for use in baits or for spot spraying of foliage but fruit cannot be picked for four days after spraying. The biologically-derived insecticide spinosad can also be used for baits and spot spraying of the foliage and fruits can be picked on the same day as spraying.
The bait is applied to the foliage as a coarse spot spray of 60–100mm for each tree depending on size. Entire tree coverage is not necessary as the flies are attracted to the protein by smell. The bait can be applied with a garden pressure sprayer, hand-held spray bottle, or flung onto foliage from a bucket with a paint brush. Make sure that the droplets are large — at least 2mm across.
As the insecticides used in baits have a short residual life, baits needs to be re-applied at weekly intervals. They also need to be re-applied if there is more than 5mm of rain.
Baiting requires care and commonsense precautions. As with any pesticide, precautions should be taken particularly when transporting and handling the insecticide concentrate, and mixing and applying bait material.