If you grow lemons and other citrus trees then you have probably seen Gall wasp.
This is the swelling that occurs on the branches of citrus trees and it is caused a wasp native to NSW and Queensland. It has made its way south to Melbourne and affects all citrus including the native citrus.
The best time to attack the problem is from winter to spring. And the best way to control; gall wasp is by pruning the affected areas away and disposing them properly.
The gall wasp lifecycle begins late in spring when the female wasps are active. They lay their eggs beneath the bark. The lava hatch and then the gall appears as they develop. They then dig their way out of the gall and mate, they lay more eggs, and so it goes.
Although the gall wasp will not directly kill a citrus tree, it will cause die back, infection and disease, and this can weaken the tree.
A healthy well fertilised citrus tree in the right position is the first step to preventing gall wasp. It is also advisable to remove any fallen fruit and prune any branches that touch the ground.
Two methods of controlling Gall Wasp
- The best method is to prune the galls off the the tree before the wasps hatch. You can tell because small holes appear in the swelling (gall) on the stem. Even if they have hatched you should still prune the old galls away. The lemon tree will reshoot and new growth will be healthy.
The pruned sections need to be disposed of by burning of placing in a garbage bag and disposed of. If pruning is to harsh for the tree, try using a very sharp knife to slice the gall off the branch, making sure you dispose of the cuttings.
- The second method, which should be used as well as the pruning method is to use a gall wasp trap. This is a sticky strip that you hang in the tree, the gall wasps are attracted to it stick to it and die.
- Natural predators include the parasitic Megastigmus wasp, and they can be used as a control method. However they are not naturally found in the cooler areas where gall wasp is a major problem.
An excellent article on Gall Wasp control is published by the Western Australian Dept of Agriculture.