Sudden Oak Death on the Ridge

These tall young coast live oak trees are growing over the roof
A few weeks ago Carmelo, he of Huerta's Tree Service, dropped by to say they were doing work in the area, and did we need anything doing. Well, yes, we did in fact. We'd been talking about the trees overhanging my dad's cottage. Long past time to trim some branches back, and remove some trunks totally.

Carmelo took a look at the oaks. "These have sudden oak death," he said. "See this black fungus here?"

Hypoxylon fungus - a sign of disease, including SOD.

The black fungus is Hypoxylon. It's a sign of SOD -- or other disease. But we have Sudden Oak Death in our area so it's likely.

SOD is a 'complex' -- it's caused by three different organisms:
  • Pytophthora ramorum, a terrestrial plant pathogen that requires water to reproduce.
  • Bark beetles (Pseudopityophthorus pubipennis) and two types of ambrosia beetles (Monarthrum scutellare, M.dentiger), which are attracted to infected areas below the bark.
  • Hypoxylon thouarsianum, a fungus that colonizes weakened trees, entering through wounds.

(Source of above: this Tree Solutions company page.) It's spreading all along the northern California coast, especially in foggy areas, and especially in areas where tan oak and California bay trees are present. The pathogen spreads often by rain drip falling from bay or tanoak trees to oaks. That pretty much describes where we live. We have a lot of bays here, and tan oaks.

Oak trees are the terminal recipients of the pathogen. For some reason - it doesn't spread from the oaks to other trees. I read this - but I don't understand it. You can leave infected oaks standing, for their wildlife value. They will die eventually.

The main resource for learning about SOD is the California Oak Mortality Task Force site.

All the oaks that needed removal showed signs of disease.
In fact all the trees where we saw the fungus were the ones that needed to be removed anyway to keep the cottage clear.

Well, then I remembered the tree behind the pool garden. It had red weeping bark, and I had not been able to find images quite like that on the websites for SOD. So I'd decided to wait and see. I really liked that little tree.

The red weeping is caused by ambrosia beetle

Leaf loss is another sign of disease.

When we looked at that tree - it too had some black fungus, now. And Carmelo said the bleeding bark was definitely another sign of SOD. And now that I stepped back to look - it didn't have as many leaves as other oaks nearby.

Well, they took that tree out - and truth to tell, I can't really see where it was!

Oak tree is gone - now you see the bay and madrone trees that were behind it.

And here is the result of the branch trimming over the cottage:

Can't really see the trimming, till you look at the Before picture.

Huerta's Tree Service does very quick, clean, and efficient work. I like them a lot and have used them before. They removed our huge eucalyptus tree, and they've done some chaparral work - they were very good at selective clearing and pruning. And their services are reasonably priced too. If you would like to see more pictures of the oak tree removal project, please do visit this Flickr set.

They stacked up the wood from the tree removal very neatly around the curve of the path - but is it too close to the remaining oaks?

You can see disease in the cross section:

I called Carmelo and asked him about their practices. They disinfect their tools and they dispose of the infected wood and trimmings at the landfill, or leave it on site as is also recommended. But I forgot to ask about the stacked wood. It is not actually touching the trees behind. And I do read on the California Oak Mortality Task Force site that it's the other trees that actually transmit the disease not the oaks, and that by rain drip. I don't think rain is going to spread the pathogen from the stack to any oaks, either. So - I conclude that this is a safe practice. What I should do is split the logs so they dry out.

SOD is a strong reason to not prune in wet months. It's been dry during the period during and after the pruning, but it would have been better to wait till summer. I read this on the Tree Solutions site Best Management Practices page:
In active SOD areas, it is especially important not to prune during the months of March thru May. This is when the pathogen is most active, especially during a wet springtime rainy season. It is recommended that the pruned material be chipped and spread out on-site. Large wood should be split and dried.
I believe I stumbled in handling this situation - I kind of backed into it. But I learned a lot. I'll monitor my oaks for signs of the disease - the black fungus and the cracked and "bleeding" bark. Next time, I'll wait till summer months to deal with it - and I will consider leaving the trees in place if they are not going to be a danger. It's probably too much to consider trimming back all the bay trees - they are prevalent here. But I'll be more aware of the situation from here on out. Your comments and suggestions are most welcome.


Jason said…
Well, at least you were going to get rid of the diseased oaks anyway. Good luck with your other trees. I sometimes think the way the pests and diseases keep cropping up all we'll be left with is ginkgo and ailanthus.
James said…
Sorry to hear about the SOD patients (victims?). Now, when I see sap-oozing oaks, I start worrying about the latest oak issue, the gold-spotted oak-borer (GSOB), which has established itself within three miles of my garden. (I hear it's headed north. Sorry.) For such big, hearty-looking trees they seem to be pretty fragile after all, especially when you add human factors into the mix...
We've considered removing a number of our California Bay Laurels, at least those in close proximity to our oaks, as they are a reported reservoir for disease. I know they're experimenting with this in the North Bay to assess whether it helps to stave the spread of infection. We lost a few oaks last season to SOD, and I'm noticing more dead and dying oaks on the road nearby. I wouldn't worry about the stacked wood, and actually think it's better to leave it in situ. Some recommendations I've seen have suggested that none of the infected material should be removed from the site at all, but up here that's not really practical, especially with the recent additional burn restrictions. I think this is a disease that we'll be living with for a long time, and perhaps more a symptom of how much our land practices have changed (such as wildfire suppression).
Country Mouse said…
Jason, we've been pretty lucky as far as disease goes till this. We did have some fungus or something blighting our big madrone but it recovered. We don't get red berries on the toyon - I understand that little routine - aphids farmed by ants make honeydew which encourages black sooty mold. So I'm more optimistic than you based on our experience. I don't know about the gold-spotted oak-borer though! Have to look that up. And I do need to look at the bay laurels - I think it is possible I could trim at least some back, and remove some babies that don't need to be growing where they are. Thanks for reading and commenting!