Alstonville macadamia grower John Pretorius checks a tree limb for stem borer control with NSW DPI district horticulturist Kevin Quinlan.

Three stem borers are posing increasing problems for macadamia growers in the State’s north east.

NSW DPI is investigating the borers which weaken branches and occasionally cause dieback in limbs and even tree death in extreme cases.

'The latest borer to emerge, a bark boring beetle known as cryphalus niger, causes pin-sized holes in the wood of the tree,' said DPI horticulturist Kevin Quinlan, based at Alstonville Centre for Tropical Horticulture.

'It seems to attack trees that are under stress,' he said.

'Whether that stress is related to the drought conditions we have experienced or due to disease or some other type of stress we are unsure.

'In most cases the first sign that people have noticed is a large loss of leaves from a tree and on closer examination the beetle feeding sites have been found on the underside of the branches.

'When we see this large loss of leaves it is usually too far gone to save the tree.'

In recent years, growers have also reported increased activity of two other boring pests - the Maroga moth larvae and the long-lived longicorn beetle.

'The Maroga attacks the branch forks in spring and summer causing dieback and branch losses, even tree death in young trees,' said Mr Quinlan.

'The longicorn beetles also attack branches, boring out the heart wood and dropping the branch with a characteristic spiral cut.

'They emerge as an adult also in spring, summer or autumn and lay eggs into exposed timber and bark cracks.

'These insects have life cycles up to five years, which makes it hard for the growers to associate damage now with a beetle flight that went through two or three years ago.'

Mr Quinlan said the best strategy for these borers is to keep trees as healthy as possible, remembering these pests attack stressed trees.

'It is best to monitor trees for signs of damage and either prune off infected branches and burn them or apply a spray treatment if monitoring finds Maroga moth activity.'

NSW DPI is currently examining the lifecycle of these different borer pests and how wide-spread they are.

'Knowing if these are wide-spread pests, localised or just sporadic will help us determinethe best strategies for control.'

Mr Quinlan said it had been a fairly good lead up to the north coast’s 2006 macadamia harvest, due to start in March and estimated to be worth $100 million in farmgate value.

Contact: Kevin Quinlan, NSW DPI Alstonville on 02 6626 2400.

- PHIL BEVAN

This story appears in Agriculture Today.