I have been battling citrus gall wasp for a few seasons now and have tried a number of methods to attempt to get rid of them. I have tried slicing off the galls, I have tried ignoring them and I have tried pruning. None have worked particularly well.
Citrus Gall wasp is a native pest traditionally living in our native citrus. Ironically my native Finger Lime is the only one of my citrus that has yet to play host to it. The wasps lay eggs in new citrus growth and as their eggs grow galls form on the parts on the branch hosting the eggs;
In Melbourne the basic lifecycle of these tiny, tiny wasps seems to be: Wasps emerge about mid to late Spring, lay eggs in new growth with the galls becoming obvious by late summer. The galls get larger as the larvae feed on the tree. The larvae continues to feed all Autumn and Winter to emerge the following Spring and so the cycle continues.
In the past I have tried slicing off the galls (described here), and pruning the tree in late winter before the galls emerge. Although the first method was moderately successful at killing some larvae it didn’t get them all and it also weakened the tree (probably more than the galls themselves would have). Pruning the tree in winter definitely got rid of many galls before they hatched. The downside was that either; I missed some or some new wasps came into the garden because the galls still came back. I suspect that by pruning in late winter I was actually giving the wasps lots of nice new growth to burrow into. With that in mind I am going to try pruning them now (Summer). My hope is that if I prune now the tree will do lots of growing and that growth will be less new by the time the wasps emerge in Spring. I will also hang some sticky strips in the trees then and hope that that gets rid of them.
My feeling is that I should keep trying to get rid of them as, while they don’t kill the tree, they do weaken it, and I think its appropriate that I try and do what I can to limit numbers of this pest. Of course given the number of citrus trees locally I might be fighting something of a losing battle…