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Kauri Dieback Symposium

Written by Erica Commers - Treescape on February 27th, 2015.      1 comments

Summary of Kauri Dieback Symposium Feb 14 & 15, 2015 Hokianga

Many stakeholders and scientists presented from Plant and Food Research, Scion, Auckland Uni, Otago Uni, Massey Uni, Lincoln Uni, DOC, Councils and committees. New science and efforts made to further the understanding of Kauri dieback and the management thereof were covered.

The Kauri phytophthora strain has been scientifically identified as new and officially renamed Phytophthora agathadicida, still referred to as PTA.

What is now better known about this pathogen:
  • It is soil borne, meaning it is introduced to Kauri (Agathis australis) via the fine roots nearer the soils surface, in which it travels up through the vascular tissue of the tree. Trees may not always be symptomatic that are infected!
  • It is transferred to new territories in soil particles, including but not limited to human footwear, feral pigs and fauna, tracks and tires, machinery with soil attached, and nursery plants.
  • In all of the research so far, there have been no identified Kauri trees that demonstrate any resistance to the pathogen- scientists are hoping to find a few eventually with natural resistance, no such luck thus far.
  • Phytophthora has the ability to be introduced to a new soil environment by dormant microscopic oospores, which can be viable for an unknown period of time in the environment, or by zoospores which are motile in the soil via water.
What this translates to for sanitation purposes in the field:
  • Consider all kauri material as contaminated when working in regions with known PTA, such as Titirangi and the Waitakeres.
  • Sanitation of footwear: Removal of all soil particles and disinfecting with Trigene should occur for everyone when walking around Kauri trees, even if the work is being done on a tree neighbouring a kauri.
  • Sanitation of tools: Clean and remove all soil particles from saws and equipment, then disinfect with Trigene.
  • Sanitation of large equipment that leaves the road: If tires or tracks operate off of paved or road areas within PTA areas, removal of the soil from tracks and tread must occur. Where this is not practical, may want to reconsider work methods or bring a brush for cleaning large equipment and acknowledge the time it will require.
  • All Kauri branch, stem, wood, foliage material: Preferable to leave on site! If it must be removed, don't chip. If a chipper is contaminated it becomes a much larger issue to clean. If mulch is created, it may harbour spores which can further be spread via the mulch product, it may not die or decompose in the mulch pile at temps.
  • It is much preferred to leave tree material in whole branch and stem form to minimize spread. Furthermore, if it is moved off site, burning may be the only method to remove the pathogen spores from circulation.
Remove soil, Remove Soil, Remove Soil!
By Erika Commers
Treescape Environmental


Ivan Earl says ...
While Phytopthora species in many parts of the world have been widespread, and injuring plants but also over 40+ years trees killed such pathogens have been chipped and composted. I doubt if properly composted once infected material has a high potential to reinfect. I stand to be corrected, however, my experience has been that the Phytopthora pathogen does not reinfect through compost. The main issue to understand is that the pathogen requires certain conditions for it to proliferate and cause damage. Characteristically, soil has to have an amount of water to make it possible for distribution to occur. Ipso facto, no water no problem. Treating the pathogen AFTER soil moisture increases effectively treats the secondary injury, and not the primary injury. AND it is for such reasons we never get on top of major issues but seek a chemical-fix because it's easier to apply than to fix the main source of a problem.
Look at: http://www.extension.org/pages/28585/composting-to-reduce-weed-seeds-and-plant-pathogens#.VO_GpfmUd8E

But also, it is futile to believe that keeping material of a certain size reduces spore circulation when at anytime every known spore in NZ is airborne. Additionally, every living being has something that kills it, and like all infected roots, other fungi reduce that to reusable organic materials in which new trees grow.
Fix the drainage; discover why there's additional moisture or its source, and I'm sure you'll fix the problem. As arborists, whatever you do don't become the problem.
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