Sunday, 30 October 2011

Why are kawakawa falling over?


In Birdwood Reserve, near where I live, there’s been an epidemic of some sort affecting kawakawa, Piper excelsum.  Large plants lose their leaves and the roots seem to die off, because the whole plant falls over, as if wind-thrown.  There are still plenty of small plants alive, so it's not wiping them all out:

Kawakawa is very susceptible to spray damage, and certainly some of these dead plants are alongside tracks where weeds have been sprayed lately.  I’ve found the slightest spray drift of glyphosate is enough to wither kawakawa leaves and slowly kill the plants.

But some of these plants were growing where I don’t think there would have been any spraying, so I’m wondering if a disease is involved.  Indeed one such dead plant is in my garden, where I certainly haven't sprayed, but where nevertheless quite a few plants (not just kawakawa, but also northern rata (Metrosideros robusta) and akeake (Dodonaea viscosa)) have suddenly died.  The weather has been normal, except for the snowfall in August. 
In cabbage trees (Cordyline) sudden decline is caused by a phytoplasma.  This is an extremely small bacterium that's spread by sap-sucking leaf hoppers.  So far it's been implicated in deaths of cabbage trees, strawberries, coprosmas, and Phormium (New Zealand flax) (Liefting et al., 2007).  I've no reason to suspect any particular cause in this case, but the cabbage tree disease does show how devastating these things can be.
I'd be interested to hear if anyone else has observed similar collapse of kawakawa anywhere.
Reference
Lia W. LIEFTING, Ross E. BEEVER, Mark T. ANDERSEN, Gerard R. G. CLOVER Phytoplasma diseases in New Zealand.  Bulletin of Insectology 60: 165-166 (2007).

11 comments:

  1. No - eek! I've often noticed kawakawa trees with leaf curl. One bush will be affected, while another beside it will be fine ... but I've not seen the affected trees die off completely. Could the leaf-curl kawakawa trees I've seen be affected by spray? Is that what happens to them?

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  2. That is what glyphosate does to them, but there might be other causes of it as well. Proving cause and effect can be difficult.

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  3. Hmm ... so could I ask your thoughts on council use of glyphosate? (Also, is it often inaccurate to call it by the tradename Roundup now?)

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  4. In principle I'm not opposed to glyphosate as a herbicide, but I also think it tends to be used a bit too enthusiastically at times when native plants are close by. I'm not sure who's to blame though; I think other players could be involved. I find about half the plantings I make in Birdwood Reserve get either cut down by weed trimmers or sprayed, and the edge of the bush is getting eroded in places, allowing wind into the forest.

    I prefer to use glyphosate as it's a more generic name; for specific instances I can't be sure what brand was used.

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  5. Okay - that's interesting - thanks!!

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  6. A reader emailed: "I've been wondering for a while what is going on with the kawakawa. We also have a few that have died recently, and a few younger ones right next to them that are healthy and happy. The dead ones started looking poorly before the snow so I don't think that that bout of bad weather killed them. I'm also reasonably certain that it's not spray. I have also noticed some sickly and dead trees in the reserve at the end of Holloway road."

    Looks like we need a plant pathologist; I'll see what I can find out.

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  7. I haven't found out any more, but I have noticed very poor fruiting this year. In fact I know of only one plant that has any fruit on it. Maybe the cold snap was more influential than I thought.

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  8. Thanks to a tip-off from a reader, I googled and found this report (see page 8) of sudden decline of kawakawa in Northland and Auckland, probably caused by Phytophthora that attacks the roots: http://www.biosecurity.govt.nz/files/biosec/pubs-media/pubs/biosecurity-magazine/issue-99/biosecurity-99.pdf
    I suspect we have the same thing, and I'm told that Landcare Research scientists are onto it. I'll try to follow up with them.

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  9. Here's the published abstract from a conference paper; I'm taking the liberty of copying it in its entirety because (1) it's freely available on line and (2) at the link there are all the papers from the meeting so one has to search the whole Proceedings to find this one:

    Abstracts: 5th IUFRO Phytophthoras in Forests and Natural Ecosystems

    Auckland and Rotorua, New Zealand, 7-12 March 2010

    18 Phytophthora Species Associated with Kawakawa Tree Decline in
    New Zealand
    Wellcome Ho1, Raja Thangavel1, Brett Alexander1, Travis Ashcroft2, Peter Anderson3 and Nick Waipara4
    1 Plant Health and Environment Laboratory, MAF Biosecurity New Zealand, PO Box 2095, Auckland 1140, New Zealand
    2 Incursion Investigation, Plants and Environment, MAF Biosecurity New Zealand, PO Box 2095, Auckland 1140, New Zealand
    3 North Shore City Council, 1 The Strand, Takapuna, Private Bag 93500, Takapuna, North Shore City, New Zealand
    4 Auckland Regional Council, Private Bag 92012, Auckland, New Zealand

    Kawakawa, Macropiper excelsum, is a small tree common in the North Island and endemic to New Zealand. During 2008-9, a large number of kawakawa trees displaying symptoms of leaf yellowing, branch wilt, and
    sudden collapse of trees were observed in Auckland and Whangarei. Kawakawa trees in Oratia, Auckland initially showing symptoms of decline have subsequently all died. Declining trees were found in poorly
    drained soil, at least temporarily water logged during the winter, while those growing on well-drained sites were generally healthy. Leaf, stem, root, and soil samples were collected for isolation of plant pathogens.
    Phytophthora isolates were recovered from root and soil samples using a cedar needle baiting assay. The Phytophthora species were identified as P. citrophthora, P. cryptogea, and two distinct Phytophthora isolates
    in the P. citricola complex based on morphology and molecular analysis. This is the first report of Phytophthora species associated with kawakawa. Koch’s postulate is required to determine the pathogenicity of these Phytophthora species. Development of disease management strategies is needed to establish an effective disease control on declining kawakawa trees.
    http://forestphytophthoras.org/sites/default/files/proceedings/IUFRO%202010%20NZ%20Abstracts.pdf

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  10. I have noticed significant die-off of Kawakawa in the Marlborough Sounds this year around Resolution Bay. The symptoms sound similar. Has been a very wet spring and only some trees are affected, mainly, I think, in the more waterlogged areas.

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    Replies
    1. Thanks Paul. Our local population seems to have recovered well, and flowering and fruiting have been good this year. The large bare patches in the bush are full of young saplings of kawakawa and other trees.

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