Protect Your Garden from Fruit Fly and Citrus Gall Wasp
Notes from the webinar by Kaye Roberts-Palmer from Blue Bee Garden Design 23.10.25
Queensland Fruit Fly (QFF) and Citrus Gall Wasp are major pests in Australia and are often a gardeners worst nightmare, so it’s a good idea to know how to identify, prevent and manage them in your own garden. You can also watch the recording of this workshop by following this link: Protect your Garden from Fruit Fly and Citrus Gall Wasp – My Smart Garden
An important part of any gardening activity is being aware of pests that can cause damage to your plants at different times of the year.
Two of the most destructive garden pests active in spring are fruit fly and citrus gall wasp.
Fruit Fly
Queensland fruit fly is a pest native to the rainforests of north east Australia. It causes damage by laying eggs into fruit, rotting the fruit as it ripens. Fruit fly is a serious pest and costs billions in damage to the agricultural industry.
Unfortunately, fruit fly populations have spread from Queensland and New South Wales down to Victoria and are now found in Melbourne where it is attracted to most fruit.
Life cycle
Adult fruit flies emerge from the soil and need to eat food (proteins found in moulds and fungi) for about ten days to become mature enough to breed.
Once they have mated, the females lay eggs in ripening fruit. Each female can produce up to 800 new fruit flies in her lifetime of three months.
The fruit fly larvae take 5-10 days to mature and suck up rotten fruit jelly to help them grow. Once mature, they chew their way out of the rotten fruit where they drop to the ground and hide in the soil.
There they grow into pupae developing a hard case as their bodies change into a fly and the life cycle begins again.
Seasonal management
During September to November Fruit fly populations will start to increase in size and overwintering adult flies become active and female flies will be looking for a source of protein which is needed for their eggs to develop. By late spring, fruit fly may have laid eggs in early ripening fruit.
In early spring use fruit fly monitoring traps to identify when adult flies are first active, as well as direct control measures such as protein bait sprays and traps. Some of the traps use an artificial female scent called Cuelure. It’s a sticky, sweet liquid that drowns the fruit flies.
During December to February fruit flies are at their most active. Adult flies are feeding, breeding, and laying eggs in suitable host crops.
Continue using the same control measures for late spring, including bait sprays and traps, and reapplying or refreshing these controls regularly and according to instructions
Any fallen fruit should be collected, placed in a plastic bag and left in the sun for 5–7 days or put into the freezer for a few days. Dispose of the fallen fruit in your green bin.
During March to May fruit flies can still be active particularly if there are available hosts and the weather remains warm.
Late ripening fruits like citrus, apples and pears are still susceptible to attack. This is the time of year to clean up unharvested fruits.
During June to August fruit flies are dormant and overwinter in sheltered locations. Eggs and larvae in fallen fruit, as well as pupae in the soil may also survive. Continue cleaning up fallen fruit.
Remember to use traps and baits at the right time and use wildlife friendly netting around ripening fruit.
Citrus Gall Wasp
The Citrus Gall wasp is a native pest from Queensland and originally preferred finger limes (Citrus australasica) to host its larvae. In the 1990s the citrus gall wasp made its way to Victoria hitching a ride on the transport routes.
When it arrived, lemon trees were a backyard fixture and with smaller gardens and windy weather, the citrus gall wasp was blown around infecting citrus trees. Without a predator insect, it has spread across Melbourne and has become endemic across our backyards.
Fortunately the citrus gall wasp has a 12 month life cycle which means this can be interrupted by gardeners at critical seasons.
Spring
In spring the adult wasp which is about the size of a full stop, stings fresh, young branches laying eggs into the heartwood. This is the central, dead wood where eggs are protected from any outside weather. The citrus gall wasp does not affect the fruit.
Summer
The citrus tree trying to continue to keep water, sugar, and carbohydrates running along its branches swells its cambium layer over the damage. This tumorous swelling is known as a ‘gall’.
Autumn
In autumn the eggs turn into larvae and begin eating the heartwood. They remain in there until spring (this is the best time to cut out all galls)
Winter
The larvae are dormant but continuing to cause damage (continue to cut out any galls).
Spring/Summer
The larvae change into adult wasps and eat their way out rupturing the cambium layer (living tissue) and leaving tiny holes in the stems. The adults will then find other stems to lay its eggs. Each wasp has 100 eggs.
Five stages of Citrus Gall Wasp infection
Stages 1-2
While your tree has good canopy coverage and fruit, galls can be seen on branches.
Stage 3
There is an increase in fruit but your tree’s canopy is thinning and the galls are much bigger and on many branches. This is because the infestation has increased to a point where you tree is very stressed. This triggers an increase in fruit production as fruit and in particular the seeds, is the tree reproducing itself to survive.
Stage 4
By this stage there is hardly any fruit or canopy and many galls have joined together to form ‘gall sausages’ lumpy tumorous growth full of developing larvae.
Stage 5
The tree unable to cope with the infestation is in serious decline but you can break this cycle at any time.
Citrus gall wasp treatment and management
The citrus gall wasp is not fussy about which type of citrus it infects, so check them all. Do this by looking at the tops and bottom branches. If unsure whether a gall is forming, run your finger along the stem. If there is a slight bump and the cambium layer (bark) looks stripy that’s a gall. Keep your tree at a reasonable height and width so that it’s easy to check for galls.
Around autumn check your tree and completely remove any galls. Take them off roughly one centimetre under the gall.
If the gall is bulging on one side, use a pair of clean secateurs to open them up and expose the larvae to oxygen. This will kill them, you don’t need to add anything to the cut.
When opening up galls or cutting them off, only use secateurs so that the cuts will be sharp and clean. If you have a bulging gall only take off what you need to. If too much of the cambium layer is removed this can ‘ringbark’ the branch and then you will have to remove the whole branch.
Other maintenance activities:
Submerge the galls for a couple of days to a week in water. This drowns the larvae and they can be put in the green bin. Avoid adding freshly cut galls straight into the compost bin or green bin.
After pruning out the galls avoid fertilising your citrus trees in spring. A burst of new stem growth will attract the citrus gall wasp.
A product called Kaolin Clay can be sprayed onto the stems in late august. It creates a powdery coating that deters the citrus gall wasp but will wash away after rains. Stay away from yellow sticky traps, they capture everything including bees and other beneficial insects.
Because citrus gall wasp can be found in many citrus trees have a chat to your neighbours and work together to remove any gall wasp infestations, so they don’t spread across your suburb.