ORGANIC FRUIT FLY CONTROL

Fruit fly is responsible for more bad language from gardeners than any other pest. If you are lucky enough to live in a fruit fly free zone then count your blessings and do your bit to keep it that way. If you live in fruit fly zone, unless you are prepared to put in effort from year to year then a chainsaw may be your best solution. Fruit fly is a pest that needs a community approach; it could be the perfect opportunity to meet your neighbours for a street BBQ so you can plan a coordinated effort.

The main fruit fly pests in Australia are Queensland fruit fly (Q fly) which is native to rainforest habitat along the east coast of Australia and Mediterranean fruit fly (Med fly) found only in WA. The fruits most commonly attacked by these flies are figs, cherries, stone fruit, apples, pears, loquats, guavas, feijoas, tomatoes and capsicum.

LIFECYCLE:

Q fly develop from eggs to adults within 5 weeks in hot weather, Med fly take only 4 weeks. The female flies lay their eggs in small groups just beneath the skin of fruit. The maggots hatch and by their feeding as well as bacteria they carry, cause the fruit to rot and drop. When the maggots are fully grown they leave the fruit and burrow into the soil, where they pupate. Adults can live for many weeks and flies commonly over-winter as adults, becoming active when the weather warms up around August and gradually the population builds to a peak in late summer.

The tiny flies that hover around the fruit bowl are fungal gnats and are attracted by decomposition; they are not fruit flies.

PHYSICAL & CULTURAL CONTROLS:

Remove any fruit from the tree with dimples or weeping clear sap. This is more effective than picking up rotten fruit from the ground as the maggots may have already left the fruit to pupate. Destroy all infected fruit by immersing it in water for several days, or placing it in a sealed, black plastic bag in the sun, then try feeding it to poultry.

Ideally it would be best to avoid planting fruit fly prone trees (see attached list). If you really want to grow stone fruit then dwarf trees or espalier trees will make management easier. A good rule of thumb when pruning stone fruit is that if you can't reach it cut it off.

The most effective organic solution for the home gardener is exclusion. This simply involves covering either the individual piece of fruit, fruit clusters or the whole tree. It sounds time consuming but can be surprisingly easy and fast compared to the process of donning protective gear and spraying a chemical control several times through the fruiting season. Commercial fruit fly exclusion bags are available in either waxed paper or cloth. In SE Asia newspaper is glued to make a bag to cover fruit. Bags should be placed over the fruit, as soon as it is formed, thin the fruit at the same time.

Excluding fruit fly from the entire tree is also possible by using a lightweight fabric such as mosquito netting, shadecloth or nylon flyscreen material. These generally need to be supported by a frame. Only leave these covers in place for the period that fruit is ripening to avoid damage to the tree. A big advantage to exclusion is it usually helps deal with bird and possum problems as well.

FRUIT FLY EXCLUSION BAGS Enjoy unsprayed, fruit fly free fruit with this organic solution for the home gardener! These imported waxed paper fruit bags come in 2 sizes, the smaller size is suitable for nectarines, peaches and persimmons, the larger size for mangoes. Early in the season, thin the fruit, then simply twist a bag over each remaining cluster of fruit, using the built-in twist-tie. Also useful for the control of codling moth. Offers some protection from birds and may last more than one season. Includes FREE information sheet on organic control of fruit flies.

CLOTH FRUIT BAGS A great idea to protect fruit from fruit fly, but strong enough to protect it from marauding possums, fruit bats and birds. Also useful for the control of codling moth. These bags are sturdy washable calico cloth with a drawstring; they can be used year after year. The fruit ripens fully within the bag. Includes FREE information sheet on organic control of fruit flies.

BIOLOGICAL CONTROLS

Fruit fly has several predators. Braconid wasps are egg parasites. Ants and ground beetles feed on the maggots. Spiders, dragonflies, robber flies and birds such as swallows, Restless Flycatchers and Willy Wagtails eat the adult flies.

Poultry are an enormous help in fruit fly control. If you design your orchard to incorporate chooks they will reward you by turning rotten fruit into eggs and happily spend hours scratching beneath trees looking for fruit fly pupae. Adult fruit flies are trapped on the ground for up to 24 hours after emerging from the pupae as it takes this long for their wings to harden. During this time the adult flies are also vulnerable to a roving chook. Where it isn't possible to allow chooks free range, small demountable fences can be used under trees vulnerable to attack by fruit fly.

LEAST TOXIC CHEMICAL CONTROLS

Pheromone traps are currently available to attract male fruit flies only, so they are useful only as an adjunct to some other form of control.

A 'softer' option to blanket spraying with a systemic insecticide such as dimethoate or fenthion is called a 'splash bait'. The yeast autolysate bait sold commercially as Q Fly Lure is mixed with an insecticide and sprayed onto the lower leaves of trees. A splash bait can be used to kill both male and female fruit flies of all species. This is not an organic solution but simply a better choice than the spraying of a systemic chemical over the whole tree including the fruit you eat. Apply every week, beginning 2 weeks before fruit becomes susceptible and continuing until harvest. This can be 90% effective. An important advantage over systemic insecticides is that you avoid causing the death of large numbers of beneficial insects, which would inevitably lead to increased numbers of other pests.

Trapping fruit flies in containers with small entrance holes is generally ineffective as female fruit flies are unwilling to enter traps. Even though it may appear as though the trap is full of flies these are unlikely to be female fruit flies. Research on a range of homemade traps has found less than 1-2% of the insects caught are fruit fly.

Recent research has found that Q fly responds best to a blue colour while Med fly responds best to yellow. Homemade traps of coloured styrofoam balls covered with a non-drying glue may catch a lot of fruit flies. Researchers in the USA have found coffee bean juice from ground up ripe coffee berries a great success as bait for female Med flies.

FRUIT FLY RESISTANT FRUITS:

Avocado, avoid thin-skinned Fuerte and Rincon Bananas Blueberry, sometimes affected Citrus, avoid thin-skinned varieties such as Meyer lemon Custard Apple, winter ripening varieties are best Grapes, sometimes affected Grumichama Ice Cream Bean Jaboticaba Kiwifruit

Longan & Lychee Mango Macadamia Mulberry, sometimes affected Nashi Pears, sometimes affected Passionfruit Pawpaw Persimmon, early varieties like Fuyu are susceptible Pineapples Pomegranate

DISCLAIMER:

No liability will be accepted by Green Harvest, its owners or employees as to the accuracy of any information. No responsibility will be taken for damage to property or persons due to information given about a product or technique. No responsibility will be taken for the loss of a crop or income due to information given about a product or technique.