The mystery of why the 100 year-old Norfolk pine trees on Granite Island are dying seems to have been solved. 

One tree was felled by high winds in July last year and the remaining five now appear to be all but dead.  

A local family discovered holes drilled in the trees last weekend, which led to speculation that poison could have been to blame.

Local MP David Basham cleared up the mystery on ABC Radio Adelaide on Monday 20 January when he revealed that the Department for Environment and Water has been trying to save the trees from a virulent white ant attack.

“Unfortunately, I was made aware of a problem over there about six months ago … following that tree blowing down, “ he explains.

It was discovered the tree was hollow and, after closer inspection, they discovered there were white ants in it.”

Mr Basham says the Department drilled holes into the trunks and injected chemicals to try and kill the white ants.  The holes were then plugged with dowels.

He concedes that the chances of the trees surviving is slim but that it is a case of, “wait and see.”

Norfolk Island pines are more susceptible to attacks by white ants when stressed, such as in times of low rainfall.   

The four trees closest to the island’s café were planted in 1918 as part of a garden that once existed on the island.