Fruit fly in the garden, and what to do about it here

Before anything else, there are two completely different insects getting called fruit fly, and almost every bit of advice you'll read online is about the wrong one. Sorting out which one you've got is the whole job, because the answer for one of them is a jar of vinegar on the windowsill and the answer for the other one is a phone call.

The one in your kitchen

The little flies hovering around the fruit bowl and the compost caddy are vinegar flies. They breed in fruit that is already overripe or split, they're a nuisance and nothing more, and they're the ones every home remedy on the internet is aimed at.

If that's what you've got, the jar trick genuinely works. Put a splash of apple cider vinegar in a jar with a drop of dishwashing liquid so they can't sit on the surface, cover it with cling film and poke a few holes in the top. Keep the fruit bowl tidy and empty the caddy more often and they'll give up in a week.

The one in your tree

Queensland fruit fly and Mediterranean fruit fly are a different thing altogether. They're bigger, they look more like a small wasp than a housefly, and the critical difference is that the female lays her eggs into fruit that is still hanging and still perfectly good. You don't see a thing until you cut it open and find maggots in it.

South Australia treats both of them as a quarantine pest and runs an eradication response whenever they turn up, which is why there are disposal bins on the highways and rules about carrying fruit into certain areas. That effort is the reason growers here can sell into markets that other states can't, so it matters well beyond your own backyard.

If you cut open your fruit and find larvae in it

Do not put it in the compost, do not put it in the green bin, and do not take it anywhere in the car.

Seal the affected fruit in a plastic bag and either leave the bag out in full sun for a week or put it in the freezer for a couple of days. Either one kills the larvae. Then it goes in the rubbish bin, still sealed.

Then report it to PIRSA. Their fruit fly hotline number is on the PIRSA website, the call takes two minutes, and they will tell you what happens next. Reporting is not getting yourself into trouble, it is how the state catches an outbreak early enough to stop it, and a backyard tree is exactly where these things get found.

What actually keeps them off your fruit

• Pick up every piece of fallen fruit. Under the tree, under the tomatoes, all of it, and do it often. Fruit lying on the ground is where the next generation comes from and this is far and away the most useful thing on this list.
• Pick early. Fruit taken a touch under-ripe and finished off on the bench is fruit the flies never got a run at.
• Exclusion is the only real barrier. Fine mesh netting over the whole tree, or individual bags over the fruit, and the mesh has to be fine enough that the fly cannot get through it. Ordinary bird netting will not do it.
• Thin out dense growth. An open tree is easier to inspect, easier to net and easier to pick clean.
• Keep the tree healthy. A well-fed tree crops in a shorter window, so there is less time sitting there ripening and less to monitor.

Two things that get repeated and do not work

Planting basil, mint or lemongrass does not repel fruit fly. They're all worth growing for their own sake and mint is best kept in a pot unless you want it everywhere, but none of them will save your apricots.

And ladybirds and lacewings do not eat fruit fly larvae. They're excellent on aphids and scale and they belong in any garden, so encourage them, just not for this job. The larvae are inside the fruit where nothing can reach them, which is precisely what makes this pest so hard.

Traps have a place, but understand what they're for. A lure trap tells you the fly is around, which is useful information. It will not clear an infestation on its own.

I'd rather tell you the unglamorous version than the one that makes it sound easy. Pick up the fallen fruit, net what you care about, and ring it in if you find any. That's genuinely it.

Shop related products

• Gyganic for Fruit and Citrus Trees 4kg. Feeds the tree, which is the part you can control.
• Brunnings Fruit and Citrus Food 2.5kg. A smaller pack for one or two trees.
• Brunnings White Oil RTU 1L. For scale and aphids on citrus. It does nothing for fruit fly and nothing claims to.
• Multicrop EcoPest Oil Insect Spray. Another oil for the sap suckers on a fruit tree.

Did you know we carry a Mediterranean fruit fly trap in store, and it isn't on the website. We don't stock fine exclusion netting or fruit bags, so if that's what you're after we'll tell you straight rather than sell you the wrong mesh. Give us a ring on (08) 8536 4333 to check what's on the shelf.

The rest of the garden range is on the website, and there's more of it in the garden centre than there is online.

More from the garden

• Feeding fruit and citrus trees with Gyganic
• Keeping pests off a zucchini crop
• The native bees that pollinate a vegetable patch

Still learning, still finding one I missed under the lemon tree. Candeece.

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