Citrus gall wasp is an Australian native insect. Its native host is Australian finger limes but all cultivated citrus can be affected such as lemons, oranges and grapefruit. Eggs are laid in new shoots of a citrus tree in spring and the tree reacts by creating a distinct gall around the developing larvae. 

Adult wasps emerge from the gall in spring and are small (2.5mm), shiny black and will live for 3-7 days. The females can lay up to 100 eggs at a time and this begins immediately after the wasps emerge. These then hatch in 2-4 weeks and the larvae burrow into the bark for 9-10 months. The woody tissue (gall) forms around the larvae and by winter the larvae pupate ready to emerge again as adults in spring.

The galls produced during this cycle disrupt water and nutrient flow within the tree and can weaken them and affect productivity. Heavy infestations will reduce fruit size and quantity over time. Galls on older branches can indicate older infestations from the previous year or 2 and this can be confirmed if you see small holes in the galls where the adults have emerged.

We recommend working in unison with your neighbours to help break the cycle and reduce the rate that your trees are reinfested each year. it may be impossible to completely eradicate them though. 

Pruning

Prune out all new galls before winter to avoid the need to treat the galls before disposing. Pruned material can be kept on your property or composted into your green bin. Some people recommend using a potato peeler to peel at the galls too. Larvae inside the galls will not survive at this time of year. However wasps can survive and emerge if done too close to the usual emergence period in spring. If you remove them from July to November then you will need to treat them before disposal.  This can be done a few ways.

-Solarising. Place all cuttings into a well sealed bag and leave in the sun for at least 4 weeks.

-Shredding or mulching.

-Burning, if permitted in your area.

Fertiliser timing

Avoid heavily fertilising trees in winter or spring. In particular, nitrogen applications, can promote excessive spring growth that the gall wasps prefer to burrow into.

Chemical control

Chemicals registered for gall wasp are only available in commercial quantities for use in commercial sized orchards and are best avoided. Horticultural glue can be pasted over galls in early September to trap the emerging wasps which will prevent reinfestation from them.