Citrus Gall Wasp Control in Your Garden

Prevention is always better than cure, and you are more likely to be able to achieve that if you are out and about in your garden regularly (see How to Prevent Citrus Gall Wasps Appearing).

Regular monitoring of your Citrus trees will ensure that a major infestation of Citrus Gall Wasp doesn’t happen. All treatments are way more effective if you can catch an infestation in its early stages. This is especially so for Citrus Gall Wasps.

If you keep at this pest and you encourage your neighbours to do the same, you will get on top of it.

A few galls here or there can be pruned off if you wish. The timing of pruning is important. Gall-affected stems should be removed before the new adults emerge from the gall in spring, leaving tell-tale small holes in the gall. So, aim to prune in autumn, winter and very early spring. Avoid really heavy pruning in late winter and early spring, which can encourage a lot of soft growth, which is a magnet for Citrus Gall Wasps. If you leave pruning until later in spring, the wasps may have already emerged! 

Pruned stems should be placed in a plastic bag and left in the sun for a few weeks. This will kill the wasp larvae inside the gall. Don’t put stems in your compost bin, as this can enable the life cycle to continue.  

A new method you might try is shaving off one side of the gall with a sharp blade or a kitchen peeler to expose the contents of the gall. This will dry out and kill any larvae inside. You only need to do one side though – if you shave all the way around the gall you will ringbark that stem.

Once you have pruned gall affected branches, give the tree a good feed with Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food to help it recover.

Citrus Gall Wasps are native insects that cause large grotesque woody galls to form on Citrus plants. The galls form in response to Citrus Gall Wasp larvae feeding inside the soft new growth of Citrus plants.

Citrus Gall Wasp adults are shiny brown-black wasps about 2.5 mm long.
Citrus Gall Wasp larvae are white legless grubs about 3 mm long. You won’t see larvae unless you cut open a gall.

Citrus Gall Wasps go through a life cycle of complete metamorphosis: egg, larva, pupa, adult. All stages of this life cycle, except the adult stage, occur within the woody gall on the Citrus plant. There is only one generation per year.

Adult Citrus Gall Wasps emerge from their woody galls during spring. In south-eastern Queensland and north-eastern New South Wales emergence occurs from mid-September to early November. In southern Australia emergence occurs sometime between mid-October and mid-December depending on the climate.

The wasps mate, and females begin laying eggs on the same day as emergence. Female wasps lay their eggs into the bark of soft new growth twigs. They are capable of laying about 100 eggs over their life of about two weeks. Several females may lay their eggs into the same twig at the same time.

Eggs hatch after about two weeks and the larvae burrow into the bark. A sheath of soft tissue develops around the larva initially, but by late December woody tissue begins to form. Then the twig swells and begins to develop the characteristic gall. Large galls may contain hundreds of larvae.

Larvae live inside this gall in individual cells for several months, after which they pupate, and eventually emerge as adults the following spring. Emerging wasps leave characteristic pinprick size holes in the woody galls. Citrus Gall Wasps are poor fliers and short lived so they mate and begin egg laying almost immediately, often into the same tree.

Citrus Gall Wasp is a pest of all cultivated Citrus varieties, with Lemons and Oranges being the most seriously affected. Its native host, the Australian Finger Lime, is becoming increasingly popular in cultivation, and will definitely be a target for Citrus Gall Wasps.

• Woody galls of various lengths. Small galls can be <10 mm long while large galls can be greater than 50 mm long and and 25 mm thick. Larger and more prevalent galls typically indicate a long-term infestation.
• Old woody galls, brown in colour, with lots of pin-prick sized emergence holes.
• The health of affected trees can decline, and fruit production will decrease.   

Keep an eye on your Citrus trees for the presence of new galls.

• Don’t prune plants heavily in winter. This will only encourage lots of soft sappy growth which will attract females Citrus Gall Wasps to lay eggs.
• Feed Citrus trees with a balanced fertiliser that’s been specially designed to feed Citrus and other fruiting trees, like Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food. 
• Keep the soil consistently moist by watering trees thoroughly a few times a week, and apply a layer of mulch around the root zone. 
• Well cared for citrus plants will recover from an infestation of Citrus Gall Wasp. Water and fertilise your plants appropriately.
• Avoid the use of yellow sticky traps in trees if you are concerned about the indiscriminate trapping of other, potentially beneficial, insects.

• There are a couple of species of parasitic wasps, Megastigmus brevivalvus and Megastigmus trisulcus, that lay their eggs into the eggs of Citrus Gall Wasps. Where these parasitic wasps are present they may reduce the damage caused by Citrus Gall Wasps.