As a counterpoint to last week’s Secret Garden, which suggested that we ought to make peace with the natural world, I want to talk this week about one of the most destructive insects on the Downs – Queensland fruit fly. If any native insect can be fairly regarded as a pest it’s Bactrocera tryoni. Without some form of intervention, it will breed to plague proportions and happily render an entire crop of fruit inedible. Does this advice contradict what I wrote last week? Not on your nelly. There are very sound practical and social reasons to control fruit flies in the home garden.
Before we discuss the various control strategies, it helps to understand what we’re actually trying to control. Queensland fruit fly looks like a cross between a housefly and a wasp about seven millimetres long. It is a native insect that occurs naturally along the subtropical east coast of Australia where it can build up in huge numbers during the summer, particularly after periods of warm, humid weather. Colder areas like Stanthorpe offer some resistance by way of winter frosts. Here, numbers build later in the season compared to relatively frost free zones, where the flies can become a problem as early as September.
Almost all fruiting plants are susceptible to fruit fly damage. The female lays her eggs in a piece of ripening fruit, and after an incubation period of just a couple of days, maggots hatch out, spoil the flesh and often cause the fruit to drop onto the ground. To help break the breeding cycle, good hygiene is vital. Clean up any fallen fruit or let chooks into the orchard to do it for you. Monitoring is also helpful. Now, late winter is the time to hang one of the various bait stations (available from nurseries) in the orchard and it should be checked weekly to get an indication of how fly populations are going. Once flies start to appear in the traps, control strategies should be implemented.
When you boil it down there are three main ways to reduce fruit fly damage: one is to spray with a toxic chemical; another is to spray/bait with a certified organic product; and the third is to exclude the flies from ripening fruit.
Short of moving to Tassie, where fruit flies don’t exist, the surest guarantee of an undamaged crop is by spraying a chemical such as Lebaycid. For me this simply isn’t an option. One of the reasons I grow fruit at home is to take back control over the stuff I put in my mouth from the dictates of multinational companies. In my backyard I choose not to use toxic chemicals already banned in lots of developed countries overseas, and the majority of backyard growers I’ve talked to do likewise.
This leaves two poison-free options for dealing with fruit fly: organic baits and exclusion. Baits have been around for years and lots of gardeners make their own using various foul smelling concoctions. These home made baits tend to be almost useless, at best attracting only the male. The females won’t enter small holes, so they fly off to mate with the blokes down the road. Hussies!
A better choice is a certified organic product such as EcoNaturalure. This next generation bait contains a natural insecticide called spinosad, and works by attracting both male and female flies with a protein rich lure. The product is “splashed” onto the trunks of trees or sprayed onto boards hung throughout the orchard. If you follow the manufacturer’s instructions closely you should get a success rate of about 75 to 80 percent undamaged fruit, but there’s one major downside. In warm districts, EcoNaturalure needs to be applied weekly from early spring until all fruit is harvested.
The other non-toxic strategy is exclusion. This works by either slipping a purpose made bag over ripening fruit, preventing access to the female flies, or by using fine weave netting to cover an entire tree. Exclusion is highly effective, however slipping a bag on every piece of fruit is very tedious, even for the most dedicated amateur. Netting is more convenient, but can be quite costly for a large home orchard.
All things considered, my approach here at Thistlebrook is to use the right control strategy for the right situation. For shy bearing plants, exclusion bags work a treat, but in my espalier apple orchard, for example, I’m planning to use fruit fly netting. In all I have more than fifty fruiting trees in the garden so the most effective, economical and practical solution is organic baiting. There’s no doubt that I’m making a compromise. But it’s a compromise I’m prepared to make for the sake of home grown fruit that’s abundant, delicious and chemical free.
First published in the Toowoomba Chronicle 28th August 2010. Photo by Kathy Kimpel via flickr.com.
