Scientists working on ways to fight kauri dieback say field trials using a common horticultural chemical are showing promising results.
Dr Ian Horner injects a young kauri tree with phosphite. Photo: Plant & Food Research
Phytophthora taxon agathis (PTA), the phytophthera pathogen that kills kauri, is widespread with the most recent tests confirming its presence in the remote Warawara forest in the Far North.
Plant and Food Research scientists have been injecting selected kauri trees in Northland and Auckland forests with phosphite, a chemical used by furit growers to ward off phytophtera.
Team leader Ian Horner said the kauri injected with phosphite showed they were able to fight off the disease.
"When the phytophthera gets on to these trees you get these bleeding cankers at the base that spread up and around the tree and eventually girdle and kill it," Dr Horner said.
"We've seen that where we've treated the trees with phosphite, these lesions stop and then heal. So that's a very encouraging sign and shows the chemical is indeed working and helping the trees fight back against the pathogen."
Dr Horner said so far his team had treated only young kauri and more work was needed to find the right dose of the chemical for big trees.
"If the dose is too high, the trees can show some phyto-toxicity symptoms, so we need to be careful that we get the rates right before we start releasing this out to the public for people to use. So we do need to be a little bit cautious about it all, but in terms of something that's very close on the horizon, it's looking very promising. "
Phosphite works by strengthening a tree's immune system allowing it to tolerate the pathogen.
Dr Horner said it was not a cure for PTA but it had been seen as one possible method of protecting high-risk or iconic trees.
He said he was confident that within two years, his team would have developed a phosphite treatment regime for kauri that would be both safe and effective.