The brown-black hairy caterpillars of the White Cedar Moth are a serious pest of the Cape Lilac Tree in the Perth metropolitan area. They are active in the warmer months, generally from October. They grow quickly and attack the tree at night by stripping the leaves. The Cape Lilac Tree is the caterpillar's only food source and there are a high number of trees in Perth, so it is an endemic problem. Many Councils, including the Town of Victoria Park, are slowly removing and replacing their Cape Lilac street trees to reduce the problem.
Hundreds of caterpillars may be seen crawling in over paths and walls to find a cool shady hiding spot during the day usually under and in houses and outbuildings. The hairs of the caterpillar can cause an allergic reaction to the skin, so it is advised not to touch them with your hands and prevent children from playing with them.
Total control of the caterpillars is impossible unless the trees are removed. Numbers can be reduced however and the best method as advised by the Department of Agriculture and Food is 'trunk banding'. Some patience is required for this method as treatment must be maintained throughout the warmer months in order to reduce numbers to acceptable levels.
- Tie a piece of hessian sack or old sheet around the base of the affected tree to form a collar and sprinkle liberally with derris dust.
- The caterpillars will congregate under the hessian to shelter from the light and heat of the day allowing easy removal and disposal.
- To ensure complete kill, collect the caterpillars (using thick gloves) and place in an enclosed container with a further application of dust. The dust will only work if it touches their skin which is why a strong dose needs to be applied to ensure it gets through the hairs.
- Bag the dead caterpillars and place in the rubbish bin.
You can spray the caterpillars directly with other insecticides such as maldison, trichlorfon or pyrethroids but it needs to penetrate the hairs otherwise it will be ineffective. The surrounding tree area, fence line, entry in to the house etc can also be sprayed. To stop caterpillars entering the house you can use rolled-up hessian, surface spray or washing powder at doorways and openings. Always read the material safety data sheet for any insecticides and do not use around children or pets.
The caterpillars can also be killed by physical means or drowning. Hot, dry weather usually kills them off naturally, as does the colder winter weather.
To report a white cedar moth caterpillar issue on a Council street tree, please call Customer Service on 9311 8111 or email firstname.lastname@example.org with your contact details and address of the property of concern. Your request will be allocated to a Parks Officer for follow-up.
On private properties, the Town of Victoria Park cannot assist with Cape Lilac trees and caterpillar issues as it is considered a civil matter.
For further information, please see the Department of Agriculture and Food website.