I have been reading and hearing a lot in the news recently concerning Sudden Oak Death, a disease that was originally a local phenomenon here in California, but has been discovered in at least nine other states, partly as a result of the commercial export of plant hosts as part of the nursery trade, some of which occurred even before the condition had been identified.

Sudden Oak Death or SOD is caused by a fungus called Phytophthora ramorum that invades the bark of susceptible species, and it can kill part or all of the tree.

In addition to affecting some of our native California Oaks, including Quercus agrifolia, (Coast Live Oak), certain plants can act as hosts for the SOD fungus - they can be damaged but not killed by the disease.

These hosts and associated plants include several species popularly used for bonsai.

Rhododendron spp (Rhododendron including azalea)
Camellia japonica (Japanese camellia)
Camellia sasanqua (Sasanqua camellia)
Lonicera hispidula (California Honeysuckle)
Fagus sylvatica (European beech)
Taxus baccata (European yew)
Sequoia sempervirens (Coast Redwood)

A more complete list can be found on the APHIS website

It's not known exactly how the fungal spores move from plant to plant, but it is theorized it can be infected soil, water or machinery (tools). However, there may be other vectors, including animals and insects.

The fact that silent carriers of the SOD disease are being found in the nursery trade suggests that we need to be increasingly vigilant about our practices. Having lost Japanese Maples to verticillum wilt, I already understand the importance of disinfecting tools.

What you can do:

PURCHASING PRACTICES
1. Avoid buying or collecting a diseased plant. Even if it seems like a good deal. In particular, avoid diseased plants known to be susceptible to verticillum wilt or SODS.
2. Stick to healthy specimens of non-host species when you can.
3. Be particularly careful with host species which may harbor the disease without showing symptoms.
4. Quarantine plants that show symptoms (sudden dieback of limbs, etc) Keep them as far as practical from the rest of your collection, and don't allow water runoff to spill from them onto your healthy plants.

TOOLS:
1. Disinfect tools prior to use and between working on trees.
2. Keep your tools clean and sharp. Hexall (disinfecting product) can be used to remove gunk and a shot of WD-40 in the hinge will help displace moisture in this hard-to-reach area.

(Suggestions on tool disinfeaction appear below)

COMPOST:
1. When a branch dies for no reason, discard / destroy it and do not compost Cut back to live growth with a tool that has been disinfected.
2. Do not reuse soil from diseased or dead trees - pasteurizing it first if you must.
2. Don't use compost bin material in your bonsai soil. Save that for your relatively inexpensive garden vegetables and flowers.


Disinfecting Tools:

I keep a supply of clorox wipes handy for disinfection purposes. Double over the wipe and with scissors you can cut right through the wipe a few times, or bite deeply into the jaws with your concave cutter, and that will distribute the bleach and help clean the tool at the same time. You can find them at the grocery store. I've included a photo below.

You can also immerse tools in 15% bleach-in-water solution. That works best with stainless tools, which will resist any corrosion created by getting water in the hinge area.

NOW, the scary part.

What happens to all those dead oaks? Do they wind up in the chipper getting turned into mulch that other people are going to use on their landscape?

Regards,

Matt

SOURCES:

http://www.oda.state.or.us/plant/ppd/path/SOD/
http://www.aphis.usda.gov/ppq/ispm/sod/
http://www.aphis.usda.gov/ppq/ispm/...ry_protocol.pdf

Attached Images

clorox.jpg (6.6 KB, 8 views)

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it's a scary thing to read. I've seen a similar article on

http://www.bonsai4me.com/AdvTech/ATsudden_oak_death.htm

Yikes! I had no idea it had a hold in the UK!

Regards,

Matt

Thank you very much for the information, Matt. I did not know about this new disease because I was not involved too much with forest pathology. I am pretty sure the disease will come on our way one of these days because it is almost impossible to control plant movement 100 %.
However, I d'ont think people should be TOO SCARY about getting the disease on bonsai because preventive measures are relatevely more simple on those trees than on trees that grow in forest or in a nursery, as I will explain.
Phytophthora is a well known genus for infecting plants especially in the vegetable family. Potato late blight is a well known examples. The fungus has been studied extensively and we know that it cannot infect plants unless the foliage or other parts remains wet for a long time. Phytophthora needs FREE WATER for zoospore and chalmydospore germination.
So, the best preventive measure for bonsai owners is to see that the leaves, bark or other plant parts of their trees do not remain wet for more than a few hours. During long rainy periods it should be easy to place the trees in a sheltered area until the sun shines again. Also, overhead misting should not last too long for the same reason. The preventive measures you mention are also good for most diseases.
Best regards, Alain

Matt, I agree with Alain. We have been on the lookout for SOD for over a year in Oregon and it has shown up in a couple of nurseries which were immediately quarantined. But phytopthera is water-born in the soil, so that is something that we do have control over with our bonsai. SOD IS an issue for us, however, when we buy potted plants from nurseries that we then turn into bonsai. So if anyone has a plant that is not thriving and has the symptoms that you have described, they should get rid of it. Especially if it is in a grow box with other prebonsai.

As for disinfecting tools, I am not sure if your method is quite enough. Oregon State Univ. has done some testing on disinfecting tools and found that the longer you can keep tools in the disinfecting solution, the better. They are now recommending 1/2 hour in a bleach solution or ethyl alcohol. Yes, I agree that is not very convenient and I very seldom do that myself, but with SOD on the loose, I just might rethink my own practices. Now that I have read Alain's intro. in the General section, I would be curious to hear his thoughts on this issue.
Moni

Hello Moni, I must add that phytophtora can not only be water born in the soil but can also be air born by the chlamydospores which can resist dessication and be transported good distances with the wind or with soil particles. Its is only after it has landed on a host plant (leaves, bark etc.) that it needs free water for germination and infection. That is why I said you must be carefull only during long rainy periods and overhead misting.
It can also live in the soil but I do not know if P. ramorum infects the roots of plants (P.infestans which causes potato late blight does not infect roots of potato plants)
However, since the fungus can live in soil it can easily contaminate tools and this is why tool disinfection is an important method to prevent its dissemination. The method of disinfection described by Matt is supposed to be quite effective for most parasitic organisms that cause plant diseases.
But I must repeat that even if contaminated tools bring pores of the fungus on the trees (bark or leaves) they absolutely need free water for many hours before infection can take place.
I hope I made my point a little clearer.
Regards, Alain

This is interesting. I wonder how the nursery container stock becomes infected in the first place? Is it there since the time of propagation? The long rainy periods with overhead mist certainly do sound like some of the climates in the Pacific Northwest, but in some areas in California where native oaks are succumbing, it is usually quite dry...

Regards,

Matt

I think nursery stock can be infected at the time of propagation (infected cuttings, soil contamination and contaminated cutting tools) or any time after by the usual methods of dissemination of the pathogen.
As for other methods of infection into the plants by P. ramorum, I think we have to wait until the research has been fully accomplished to know exactly how they can be achieved. Maybe the fungus can inter the sap of trees by contaminated insects that wound the bark (like dutch elm disease) or by other mechanical wounds that can remain wet long enough for the fungus to enter.
What I was referring to in my last posts was only in reference for what is well known from the studies carried out with Phytophtora infestans which causes potato blight. P. ramorum may have other methods of infection which will explain why it can infect plants in areas, like in California where it is relatively drier.
If this is the case, I think susceptible bonsai plants should never have open wounds on the bark of trunks or on branches that remain wet for long periods.
Regards, Alain

Thanks, Alain. I am mostly familiar with Phytophthera root rots. They are very common here in the Pacific Northwest. These are water born in the soil. SOD is still fairly new to us. I did just read an article about a "new" SOD found that is European in origin and how that strain is more virulent than even the one first found in California. Now the concern seems to be whether these two strains will combine into something even worse.
Moni

If you want to learn more about the phytopthera species, including SOD here is my source at Oregon State. You will find it mostly talks about root rots but it also helps define how nursery stock can get infected. IF I were as clever at the computer as the rest of you, I would be able to make this just a click away. Oh well. Copy and paste works too............

http://plant-disease.ippc.orst.edu/...fm?article_id=4

Interesting yet serious.
Moni