Phosphite Offers Hope for Infected Kauri

(Published on 17th February 2017)

A cure for Kauri Dieback may still be a fair way off but recent trials involving injections of phosphite offer real promise for the management of this devastating disease that causes bleeding lesions which spread and ultimately kill these magnificent trees.

Dr Ian Horner from Plant and Food Research is one of New Zealand's foremost scientists studying this issue.  Dr Horner has been conducting trials where selected kauri trees at sites in Northland and Auckland forests have been injected with phosphite, a chemical commonly used by fruit growers.

In a recent interview with Simon Smith from FairfaxNZ Dr Horner described his excitement at the results from three trial sites that he has been running over the last five years.

"We've found that where we've injected the trees with phosphite the lesions have pretty much stopped spreading, and healed. In comparison, the trees that we didn't treat, the lesions have kept growing in most cases."

‚Äč"Healing could be seen after six months with fresh bark now showing underneath old lesions that have crumbled away."

"Canopies though are not showing much sign of regrowth, yet – but it takes a long time to turn a kauri around," Horner added.

The focus of early studies has been on smaller trees, but testing has now been extended to include larger kauri up to three metres in diameter. Looking ahead the challenge revolves around finding the right dosage of chemical for big trees. Overdosing could result in trees demonstrating phyto-toxicity  symptoms while too little chemical will not provide the protection needed to halt the rapid spread of the disease.

Phosphite works by strengthening a tree's immune system allowing it to tolerate the Kauri Dieback pathogen. Therefore it should be seen as a management tool rather than a cure.

While the phosphite is shaping up to be a powerful ally in the management of Kauri Dieback, preventing it's spread remains our most important tool. Landcare Groups and community volunteers who work with NZ Landcare Trust are actively engaged in pest control and other biodiversity enhancement work within areas where kauri are present. Groups such as Manaia Landcare understand that Kauri Dieback spreads through the soil - even small quantities on the sole of a boot can be enough to introduce fresh infection. Therefore measures such as wearing 'boot covers' that restrict soil movement can make a considerable difference, and allow important pest control work to continue.

For members of the public who visit forested areas where kauri are present, the following measures will help prevent spreading the disease:

  • Make sure your shoes and equipment are clean of dirt before visiting kauri forest.
  • Clean your shoes and any other equipment that comes into contact with soil after every visit, especially if you intend to visit other bush areas.
  • Keep to tracks at all times. Any movement of soil around the roots of a tree has the potential to spread the disease.
  • Keep your dog on a leash at all times. Dogs can inadvertently spread the disease if they disturb the soil around the base of trees.



More information about Kauri Dieback disease and how to prevent it from spreading can be found at the Keep Kauri Standing website -





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