Have you noticed strange lumps appearing on the branches of your citrus trees? This is usually a tell-tale sign of Citrus Gall Wasp. This is an Australian native insect from NSW and Queensland that affects all citrus. It is now an established pest across Perth.

The adult wasp lays its eggs inside the stem of the tree in September. After they hatch, a woody gall forms around the larvae usually on young green branches. The growing insect lives off the sap of the tree. Although an infestation of the gall wasp may not kill the tree, the damage it causes is unsightly and can weaken the tree. Repeated attacks can lead to leaf drop, spindly growth and make the tree unproductive.

The galls start to be visible in February and are easy to see by June. The best time to check and remove the galls is from April to June before the adult wasps emerge and begin laying their eggs. Inspect the new young growth on all citrus trees and look for any galls forming on young, green twigs.

If the galls are present on older branches, they may be from the previous year. Look closely at the older galls for small holes which show that the= adult has already emerged.

Pruning the galls is essential for controlling this pest. Prune off new galls before th end of June. The larvae inside the gall will not survive without food and the gall wasp will not mature. Pruned material should be disposed of in general rubbish, not in compost heaps.

Galls removed after June may have more mature larvae that will emerge as adult wasps. Treat these galls by placing them in a sealed black plastic bag and putting the bag in full sun for at least four weeks. The heat from this process of solarising will kill the adult.

Spring is the time to manage the spread of the Gall Wasp as well as disrupt its life cycle. There are no insecticides registered to kill adult citrus gall wasp. Available products target either the developing larvae in the galls or work to disrupt the egg laying during the wasp emergence period in spring.

Key strategies for Gall Wasp management at this time of year are:

– Avoid heavy fertilising in winter and spring. The new growth is particularly attractive to the adult wasp and can encourage infestation.
– Apply Green Life Clay Spray to the spring growth in September to Novemebr. This acts as a repellent and can disrupt egg laying.
– Pest oils, such as Searles Ecofend Insect and Scale Spray can deter gall wasp adults from laying eggs.
– Tree Guard Pest Barrier (a sticky material made from natural gum resins, vegetable oil and wax) can be pasted over galls in early September to trap emerging wasps, disrupt egg laying and prevent reinfestions.

There is a comprehensive guide to Citrus Gall Wasp identification, management and control at https://www.agric.wa.gov.au/plant-biosecurity/citrus-gall-wasp-control

This is intended as general information only. Please ask one of our horticulturists for specific advice for your situation.