Thursday, December 10, 2009

Organic fruit fly controls

There's one thing getting in the way of Australia's great tomato-growing climate and us enjoying bumper crops of tomatoes – and that's the fruit fly. This tiny insect likes to lay its eggs in all sorts of fruits, including tomatoes. When the eggs hatch into grubs inside the fruit, it is quickly ruined. It's so disappointing to cut open a tomato and find someone else, a lousy little larva, already enjoying it. Fink.

The closer you get to the tropics the worse the problems with this pest become, but temperate Sydney is plenty warm enough for this insect to be a serious pest here too. As most of us backyard food gardeners are doing everything organically, the big problem is controlling insect pests organically. It's not easy.

It certainly can be done, but it needs persistence to succeed. Fortunately I am just the sort of persistent nutter that organic gardening needs as a recruit, and so I thought I'd do a blog about the two different organic pest control methods I am using this summer to control fruit fly. One is hi-tech and uses modern, organic, low-toxic products which are the results of excellent science. The other is low-tech and comes from my kitchen cupboard. Both work.

First, the hi-tech gear. Both Nature's Way Fruit Fly Control and Eco-Naturalure are based on Spinosad, which is derived from naturally occurring soil bacteria. This ingredient is now widely used to control various insect pests in gardening and commercial agriculture. When you open the bottles, both products are a thick black gloop which you mix up in a small spray bottle with water, and spray near (but not on) the crops you want to protect.

You should not spray the product on the fruit itself, as it is designed to attract the insects. Once they ingest the liquid, it then kills them. Pictured here, it's sprayed on an outlying tomato plant leaf (I spray it in several spots each time, and not in the same spot repeatedly, as doing that can lead to other problems such as sooty mildew).

Each product sounds great in theory and works OK in practice, but they do wash off in rain, so you need to re-apply them after rain. And you need to reapply them after several days anyway. You absolutely need to fully read the label before using either product. They are safe to use and won't harm you or your plants, so that isn't why you need to read the label. You just need to mix it up correctly, then re-apply it fairly often in the right places and at the right time. Use it incorrectly and it might not work, and as they aren't cheap that's just a major waste of money.

However, as a back-up system to the fancy products I have also set up a Vegemite trap for fruit flies. This worked well last year, but be warned, it catches lots of ordinary flies, not just fruit flies. It's gruesomely effective! So here we go...

If you don't know what Vegemite is you obviously aren't Australian. Ask an Aussie about it the next time you meet one. It's a breakfast spread for toast or bread. However, it is an 'acquired taste' that should be spread very thinly, especially if you're a Vegemite newbie. I love it, as many Aussies do. For a fruit fly trap you need 1 heaped teaspoon Vegemite, dissolved in 500ml warm water.

The warm water just makes it easier to dissolve the Vegemite. Give it several good stirs, as it does take a while for all of it to dissolve.

Next, pour the liquid into your trap. To make your trap you'll need a couple of clear plastic soft drink bottles and a bit of wire to hang it up somewhere.

This is a fairly deluxe Vegemite fruit fly trap, actually. We cut the top few inches off one plastic drink bottle to make our 'entrance' funnel, then cut a hole in side of another bottle and stuffed the funnel in. A simpler design is to just make several holes around the middle of the bottle to allow the flies to enter the bottle and find out what is that alluring smell in there!

As you can see, this large entrance funnel just makes it a little easier for the flies to land and wander in. Or at least that's the theory.

In the top of the bottle, just under the screw cap, we punched a hole in either side and threaded some wire through to make a handle to hang the trap somewhere. Last year we hung it near some tall staking tomatoes, and God it looked ugly!

So this year I have discreetly placed the aesthetically-challenged killing machine very close to my Alaska tomato plants and hopefully it will prove as deadly and attractive as it was last year. I've watched these fruit flies in action, and they are great wanderers and seekers. I am sure they will find my trap, check in but never check out.

Finally, the reason for all this dastardly insect warfare – my babies. The Alaskas ripen daily, so too the Beaver Lodge Slicers across the way. The taste test is only days away, and I don't want to cut open my first tomatoes and find grubs inside. Now that would be a horror movie!


Liss said...

Interesting!! Will definitely be laying traps next spring!

We had an infestation on the silverbeet about 3 weeks ago when we had that spate of hot weather. I did the garlic, chilli, beer and water method (boil, leave overnight, drain and spray) and it did the trick, we kept it up every day for about 2 weeks and now we do it every other day - haven't seen any since.. but next year I'd rather just trap them first up! Vegemite too, excellent!!

Ami said...

Hi Jamie,
Timely advice. My new baby tomatoes seem to be suffering the fate you're describing. As I type I'm dissolving a spoon of vegemite!
Yesterday I sat and stared at one of my tomato plants for ages trying to find the culprits. I did find a green caterpillar. He got squashed! I'm going to set the fruit fly trap today and also sprinkle with vege dust. Hope that does the trick!

Chandramouli S said...

That's interesting to know, Jamie. Quite informative post. It sure would help me when I start my tomatoes. [thumbs up]

Onesimus said...

Hi Jamie,
The only time I tried a version of the vegemite trap I caught plenty of ants and earwigs but didn’t find any fruitfly – they were too busy infesting my peaches and tomatoes.

I’ve given those kinds of fruit a break for a couple of years. We ripped up the peach tree and made more room in our back yard for other things. There’s a more than bountiful supply of peaches and other stone fruit available at several nearby orchards (It’s my town’s major industry).

Prior to moving into the house ourselves, we had it rented out for a couple of years. The fruit trees were neglected by the tenants, perhaps making it ideal for a fruitfly invasion. More than three years after we are still finding peach stones around the garden where we assume the fruit was left to rot.

I’ve tried tomatoes again this year, hoping that the break will have eased the problem.

As for vegemite, I don’t mind a thick spread on my toast, but I’ve been eating it for around 40 years and have developed immunity.

Jamie said...

Onesimus: hee hee, I like the immunity comment!
My Vegemite trap did catch quite a few fruit fly last year, but its main customer was ordinary house or garden flies, which are much bigger than fruit flies.

Ami: for the caterpillars I use an organic spray called Success, but Dipel is a very similar thing and is also organically OK. They both seem to work well.
And for the aphids and whiteflies I use PestOil (it's organic, and another product called Eco-Oil is much the same).
Both of these come as concentrates which you just mix up with water. They're totally safe for humans to use, and our plants too. I also use the PestOil to control scale and aphids on my citrus trees and scale on my bay tree, and I spray it routinely (ie, every month or so, whether problems are visible or not – so it's used as a preventative spray more than a "zapper" spray.)

Ami said...

Thanks Jamie for your advice.
I'll let you know how I go.

Thiruppathy Raja said...

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degarfs said...

Hi Jamie, do you have any similar remedies for trapping ants outside the house? They also invaded the soil in my pot of plants :{

Jamie said...

Ants move in mysterious ways, and are much harder to trap or deter. One natural remedy which a naturalist at the Australian Museum told me works quite well is to sprinkle talcum powder in spots where you don't want them to cross. See if that works.

degarfs said...

Thanks again Jamies! Good to know, I will try it out :D

degarfs said...

Hi Jamie,
I am looking around for Citronella plants (Geranium Citronella or Pelargonium Citrosum) for mozzie repellent. Do you know where we could find this in Sydney? :) Thanks

Jamie said...


As far as I know the citronella plants don't work anywhere near as well as is claimed. The best protections are to reduce all puddles of water around the house (ie, dishes under pots, blocked gutters, etc); try to open up your area so more air flows through; then use citronella candles, or mozzie coils if the problem is still quite bad.

degarfs said...

Thanks Jamie for the advice :)

Mira said...

Great idea thank you Jamie

davewastech said...

Re : fruit fly traps for Qld fruitfly
Do they actually work?

Jamie said...

If you mean the traps based on Spinosad, yes they do work if you persist with them. Being an organic control, they are not "set and forget". You do need to check them regularly and sometimes set them up again if rain washes away the bait, etc.

If you mean the traps based on Vegemite, yes they do work but they have the problem that they catch lots of other insects, too. These traps are also not "set and forget". Renewing the trap occasionally does help.

davewastech said...

Hi Jamie,
I've got a few young fruit trees that I planted here in Sydney 2 to 3 years ago. So I will start experimenting with the vegemite traps now. So far I just bag my pepino fruits in organza bags and net the yellow cattley guava tree. Other fruit seemed to have mostly escaped the little blighters' attention so far (persimmon, red cattleys, panama berry, wampi, pawpaw, emperor mandarins, lemon, nelly kellie passionfruit and cherry tomatoes). Maybe I've been a bit lucky, but I do make sure that I promptly pick up any fallen fruit. Interesting that the fly go for the (yummier) yellow cattleys, but not so far for the common red cattleys. Prior to this garden my only gardening experience was in Perth which of course has Mediterranean rather than Qld fly, so I'm very much just starting to learn about the Qld ones.

Unknown said...

Since December I've been trying the vegemite traps. 10 traps in my garden using various recipes eg vegemite, vegemite + sugar + yeast, vegemite + banana. And since then the fruit fly damage to my fruit trees is the worst since I've started growing fruit here in Sydney 3 years ago. Half my wampi fruits were ruined this time. Probably I should have started much earlier in the season before they build up in numbers. Maybe the traps attract more fly than they kill?
Jamie I read your other thread "Crop failure - Oh well" where you said "But I have also learned that the new 'organic' fruit fly sprays are of dubious usefulness. I was so thoroughly diligent in applying, then re-applying them again and again, exactly as per the directions on the pack. And still the fruit were attacked. I found the fruit fly spray was a monumental pain in the neck to constantly re-apply after rain, then again after several days if there hadn't been rain. And it was expensive. At $27 for a 200ml bottle – which wouldn't be enough to last one whole growing season ...."
So maybe netting or exclusion bags is a better solution, at least for small trees like fuyu, wampi, etc. What's your opinion?

Jamie said...

Exclusion bags may well be the way to go.

Unknown said...

Hi Jamie and readers,
Some feedback on my struggle with Qld fruit fly in my Sydney home garden.
Plenty of them about. They even heavily infested my (still green) bell chillis.
Last summer, in addition to the vegemite, sugar, yeast and banana-skin traps, I also tried ammonia and yes urine homemade traps, with or without detergent. I would set 10 traps at a time and place in shady spots in or near fruit trees.
End result - little, possibly zero fruit fly caught. Quite a few other bugs like flies, cockroaches, etc caught though. It's a bit difficult to identify small kill in a solution of rotten vegemite and decaying bugs.
It looks like fruit fly simply prefer to go for real fruit, and there's quite a few fruit trees around here. I read that the experts are indeed facing such a problem with their traps. See
So maybe these traps sometimes work, or at least marginally.
I've also read that fruit fly can travel some distance, although I couldn't find out whether that's meters or kilometers. Even if we catch a few ff there's going to be damage from the ones we don't catch.
So far I've found the best way to reduce my losses is to use netting or exclusion bags, and to be diligent making sure no rotten fruit lingers in my garden either on the tree or worse still on the ground. I've also taken to eating my cherry guavas a bit green before the larvae hatch out. Better green than an infested mess.
Well at least these traps don't cost much money, and are non-toxic.
Most varieties of cherry tomatoes are seldom attacked. (the big toms are more challenging)
I'd be interested to hear from others what their experience has been of ff traps.

Unknown said...

I think it's a rather aesthetic trap. Embedded in the soil, with beer (or a yeasty, sugary equivalent) it will work for slugs and snails. So it's multifunctional too! Thanks for sharing.

Unknown said...

Hi guys,
Just one small correction to my last post (1 March). Although Qld fruit fly is the big problem in Sydney, I have been told that the little maggots in my bell chillies are actually the maggots from a moth. They look like FF maggots but a bit bigger. The guy that told me couldn't remember the name of that pest, but I believe he is correct that they are not Qld ff. The chilli goes horribly rotten before it's even partially ripe.

Hi Cecelia - thanks for sharing re snail traps.

Unknown said...

On the subject of PestOil, it is a petroleum based product. Through the bromilead people I discovered an organic white oil that is sucessful with white fly here in the tropics. Bonus is that unlike petroleum based products, it breaks down in direct sunlight and washes away!!! No burning, no residues.
Canola White Oil.
Canola Oil 750 ml, "Sill" Detergent 3 tablespoons full and water 1250 ml. I usually mix this in a two-litre milk bottle and shake it violently. You can use a blender. Let the white oil emulsion rise to the top. Put a small hole in the bottom of the milk bottle and carefully open the lid. Drain off all the excess water and detergent then put the white oil into a new milk bottle. You will find if fairly quickly separates back into oil and water layers. It should be used fairly promptly when fresh. You will find with time that the white oil left behind will stay as an emulsion longer and longer. This can be explained chemically but not here. The message is make big batches and store it. Each time you use it shake it well.
Canola White Oil Spray - How to mix it.
Canola White Oil 300ml, vinegar or ammonia 300ml water 4 litters.
Vinegar-brand does not matter.
Ammonia, stick with "Superior" brand as my tests in 1997 have shown that it then did not have any phytotoxic detergents added. It is also the cheapest, per unit of ammonia present, that I have found.
Detergent I have only used Sill and Alginox

Jamie said...


Thank you for your valuable updates. I'm very conscious that my original posting was in 2009, 8 years ago, and much of the info in it is out of date or inaccurate. I just hope that people being led to this posting by Google searches (and it does seem to score a fair few hits) then bother to read all the way through to the bottom of the comments and find your update.

Regards, and thanks