A guide to the many methods available to control this pulp-plundering orchard pest
If you’ve done any research into controlling Queensland fruit fly, you’ll know that it’s easy to become overwhelmed. Heck, I’ve been trained in best practices for managing it, and I found the plethora of control options astounding. When fruit fly turned up in my orchard, I wasn’t sure where to start, despite my training. To consolidate all my knowledge, I’ve put together this post to help me decide what’s next in my own orchard. Hopefully it will provide clarity for you too.
In Part One of this three-part series I discussed what I’ve learnt in my two-year journey with this new-to-me pest. It’s worth familiarising yourself with the post to give you context for this post.
Control strategies: there’s no one size fits all
Every garden is unique, and every gardener approaches things differently (more on that here). There are many control strategies available for managing Queensland fruit fly, and the method(s) you might choose will depend on many factors, including:
- your preference for organic vs inorganic methods
- your willingness to potentially sacrifice “good” bugs that could get caught up in your control methods
- the amount of time you have available to monitor the issue and maintain your efforts
- your budget
- the scale of your garden and the size of the trees needing protection
- the types of fruit trees involved
- the timing of your harvests
- your neighbour’s approach to control (if any)
- how big the fruit fly population has become in your area.
All control options have trade-offs. For example, we’d all prefer cheap or no-cost control strategies. But low-cost options may require more frequent monitoring or may not be as effective as more expensive options.
There are many different control methods available, so in the interests of brevity I’m limiting the scope of this post. I’m only going to discuss control methods that I’m considering for my own orchard. Most of those options are certified organic targeted approaches. I could bomb the place with broad-spectrum chemical pesticides, but that doesn’t align with my values, so I’m not going to include those methods here. For information on those and other methods, scroll down to “Further reading and resources” at the end of this post.
Orchard inspections
The number one rule for managing a Queensland fruit fly outbreak (i.e. preventing it from becoming bigger) is this: prevent fruit from falling to the ground. Monitor your fruit trees and pick fruit as it begins to ripen. The timing of the Queensland fruit fly lifecycle is very specific. The female lays her eggs in fruit that is on the cusp of ripening, allowing the maggots to mature just as the fruit does (in my experience, the presence of the maggots causes infested stone fruit to ripen faster than the uninfected fruit). When the ripe fruit falls to the ground, the maggots are ready to make a swift exit into the soil to undergo the next stage of their life cycle – pupation.
Pick your entire crop of fruit just as it is beginning to ripen (most fruit will continue to ripen once picked). I patrol my orchard every second day looking for sting holes. Fantastic observation skills are the key to using inspection as an effective control measure.
I know, I said I don’t want to do anything that relies heavily on frequent monitoring, but for me, wandering the orchard in autumn isn’t arduous. I’m usually visiting it this frequently anyway. Finding each infested fruit is akin to winning an anti-lottery. I feel like a winner for spotting them, even if the prize is rotten, maggoty fruit. I freeze overnight any suspect fruit before adding it to the compost.
Insect netting
Using fine weave insect netting is an incredibly effective way to manage Queensland fruit fly outbreaks. I net my tomatoes to exclude rampant hungry blackbirds and it creates a microclimate to help the tomatoes establish and to extend the growing season (more on that here). When I first designed and built my tomato growing systems, I had the foresight to purchase insect netting because I knew that one day Queensland fruit fly Armageddon would arrive. I’ve never had a maggot in my tomatoes.
A few considerations if you’re planning to use insect netting:
- The netting must be well away from the fruit because the female fly can sting the fruit through the netting if it is touching the fruit. Use poly pipe or an alternative framework to keep the netting clear of the foliage and fruit.
- The timing of the netting installation is critical. It must be installed before the fruit begins to change colour. I find that the cockatoos descend to eat fruit in early December, and if you are beating the birds then you should be beating the Queensland fruit fly too.
- Not all netting is created equal. You get what you pay for. Some of the cheap stuff will develop runs or ladders if it gets a hole in it. Anything without UV stabliser rapidly deteriorates. If you are going to invest in a heap of plastic, then try to buy a product that will last. Avoid instant landfill.
If you have different sized nets for specific trees then consider labelling each net to make it easier to sort them each summer.
Queensland fruit fly lures for males
Hormone-fuelled young humans flock to nightclubs to flirt with members of the opposite sex (at least they did in my day; nowadays online dating has probably usurped this messy, drunken rite of passage). The Queensland fruit fly equivalent of a nightclub is the top of a tree – it’s called a lek site. This patch is marked by pheromones emitted by males.
Parapheromones are synthetic ingredients the male consumes to supplement his own pheromones. The male Queensland fruit fly’s chances of finding a mate are increased if he eats these parapheromones, and he does so greedily. The most common parapheromone lure specifically for attracting male Queensland fruit fly is cue-lure. Some parapheromone based traps for catching males can be placed as far apart as 200 metres and they’ll still do a reasonable job of picking up any randy blokes in the vicinity. Others cover distances of only 20 metres.
I’d need only five traps laced with cue-lure to cover my entire 6-acre property. A suburban block needs only one. This makes cue-lure traps cheap to implement and ideal for monitoring fruit fly populations. It’s important to note that whatever area these lures cover, they will only ever attract a certain percentage of male fruit flies. They’ll never be 100 per cent effective, and a female fruit fly needs only one male to continue the life cycle. Traps for male fruit fly are best used as a monitoring tool
Set up your cue-lure traps for catching males early, ideally a few weeks before you expect the flies ot be active. In my cool-tmeperate climate that probably means Christmas. But in warmer areas, like Melbourne, you probably need to deploy them much earlier in the season. Wait until you start catching males before you unleash more expensive or time-consuming control methods. After all, the males are just hormone-drunk louts – here for a good time, not a long time. If you want to protect your fruit, you need to target the females. But she’s wily and has other things on her mind.
Queensland fruit fly lures for females
The female Queensland fruit fly isn’t interested in parapheromones like cue-lure. Instead, she’s keen to settle down and find the right conditions in which to raise her offspring. She’s on the lookout for two things:
- A female fruit fly can lay 100 eggs per day, and producing all those eggs requires a lot of protein. The more protein she can consume, the more and healthier eggs she will produce.
- Fruit at the early stages of ripening – a host for her babies. Once her eggs are ready, she needs fruit in the optimal early stages of ripening. It’s thought she primarily uses vision – looking for yellow, red and UV light as a signal – to locate ripening fruits, scent may also play a role.
A good way to catch a wily female Queensland fruit fly involves using the smell of yeasts on ripening fruit (a primary protein source for fruit fly) as bait in a yellow trap. Protein traps may also catch a few males too. He needs to eat, just not as much as his egg-producing better half. Protein-baited traps are termed “female biased”
Protein smells are much more localised than parapheromone smells; they won’t waft on a mid-summer breeze at sunset like parapheromones will. A female-biased trap will attract flies over a radius of only five to ten metres. That means they need to be spaced more closely than the male traps and therefore they’re a lot more expensive to implement.
It’s important to note that other types of insects will be attracted to the protein smells, whereas cue-lure parapheromones attract only male fruit fly. There’s always a trade-off.
Trap choices
You’ll need traps in which to place these fancy gender-biased lures (most traps allow you to use either male or female-biased lures interchangeably. The range of options is overwhelming. I’m keen on using traps that are:
- It’s been shown that traps with a yellow base tend to be better at attracting the females.
- long-lived. If I’m going to shell out a heap of money on plastic, I want it to last. I’ll buy traps that are UV stabilised.
- I want to re-use these traps year after year and have the option to use either cue-lure or protein baits.
Traps generally use one of three different mechanisms for killing the fruit flies:
- A broad-spectrum insecticide that kills on impact. This insecticide will need renewing as it will degrade over time.
- A sticky insert that the fruit flies adhere to. Sticky inserts need replacing as they lose stickiness – at least every season.
- Drowning in a liquid. This makes monitoring difficult as the flies will quickly decompose and make identification difficult.
I’m keen on organic methods, so I prefer the sticky insert method. Biotraps are one example – they’re apparently long lasting and reusable. You can buy replacement lures (the traps can be used with either male or female attractant) and replacement sticky inserts. These traps are available from various retailers. Consider joining forces with your local community garden or gardening club to bulk buy and help reduce costs.
DIY traps
Of course, you don’t need to buy traps at all. You can make your own using old soft-drink bottles. There are quite a few recipes out there. Reader Eileen discusses her approach here. Agriculture Victoria has its own recipe here. Others have recommended watering down the juicy mush left over from infested fruit that’s been frozen. Although it’s messy, I like the sound of this – fruit juice is so expensive. I’d add a bit of cloudy ammonia into the mix; it mimics the smell of decaying organic matter and fruit flies are attracted to it.
Note that DIY traps are non-specific. That is, they’ll catch all sorts of other arthropods. I tried using these during my first infestation wave and I’m not sure that I did catch any Queensland fruit fly, but I certainly did catch plenty of European wasps, earwigs and other critters. There were quite a few good guys, such as honeybees and lacewings, in the mix too. Never add honey to the mix – it will attract bees.
I like how cheap these are to implement, but the broad range of species that they attract and the need to keep them topped up with fresh liquid puts me off. Also, whatever you trap quickly begins to stew in the mix, which makes identification difficult.
Spinosad baits
Another targeted organic control option is using baits laced with the insecticide spinosad. Much like Bacillus thuringiensis or BT (used for treating caterpillars on brasscias and loopers on tomatoes), it is derived from bacterial culture and is a naturally occurring toxin (hence the organic certification). Scientific testing shows it to be relatively harmless to mammals. Like BT, the toxin needs to be ingested by the target insect to kill it.
To reduce Queensland fruit fly populations, the toxicant spinosad is combined with a protein attractant to target females. Commercial spinosad-based products are available for the home gardener and in bulk for orchardists. Combining the toxin with a lure biased to the Queensland fruit fly means the bait shouldn’t have an impact on innocent bystander insects (but it could).
The baits can be placed on the trunks of trees, on the underside of leaves, or on posts or other infrastructure. However, Queensland fruit fly tends to hang around high in trees. Placing baits 1.5 to 2 metres above ground in the tree canopy will maximise their effectiveness (this is also a good guide for trap placement). The spray form of the product needs to be re-applied at least fortnightly, but ideally weekly. Rain will wash it away, so you’ll also need to reapply after each summer downpour.
Given the need for repeat applications this is not a treatment option that I’m likely to pursue. It sounds too much like hard work to me.
The approach I’m taking this season
I constantly observe all that is going on in my garden and orchard, and sting hole patrol is just an extension of this, so I’ll keep up the orchard inspections.
I’m tempted to let the Queensland fruit fly run riot for one or two more years to help me better understand them. If I decide that control is necessary then it will probably take the following forms:
- I’ll net some of the susceptible trees – it seems bonkers to need to do this inside my netted enclosure, but that might help.
- I’ll use male traps with sticky inserts to monitor for peaks in population – it’s cheap and doesn’t require much maintenance, just regular checking. In my part of the world, they won’t need deploying until just before Christmas, and one pheromone lure will probably last all season. Folks in warmer climates might look to get their traps out much earlier in spring and replace the components mid-season. I’ll use five male traps: one on each corner of the property, and one right in the centre of my orchard.
- I’ll deploy traps with female-biased lures near the most susceptible trees to try to reduce Queensland fruit fly’s impact.
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What about you? What strategies have you tried to manage Queensland fruit fly? What experience can you share to help reduce the impact of this dreadful pest? Please leave a comment below.
This is an important topic, so I am making this post available to all readers, free and paid. Please share it widely to support others battling Queensland fruit fly.
Further reading and resources
Eileen’s Queensland Fruit Fly Success Story
Queensland Fruit Fly Part One: Know Your Enemy. A summary of what I’ve learnt about this pesky fruit felon thus far
Queensland Fruit Fly Part Three: Outside-the-box Strategies for Control
Queensland Fruit Fly Yarra Valley
Booklet: Fruit Fly Management for Fruit and Vegetable Growers
