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Phytophthora cinnamomi in Cork Oak in Northern California

Discussion in 'Homeowner Helper Forum' started by djhnd, May 6, 2018.

  1. djhnd

    djhnd New Member

    Joined:
    May 6, 2018
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    Location:
    Marin County, California
    Greetings - I joined this forum to ask this question of experienced tree people. This is a 50+ year old tree, probably 30-40' tall with an enormous canopy - probably 50'-60' in diameter. A big beautiful tree that has had this problem for the past 1.5 years. The cork has never been harvested, so it's super thick. The cankers appear to be mostly on one side of the tree (south) though I now see a small spot on the east side. To my eyes, I'd say the tree is far from being girdled though, at the rate of progression I've seen in the past year plus, this could be a pretty aggressive case.

    Bear with me, here is the backstory:
    a) I'm a tenant. I want to save the tree if possible, it's one of the best features of where I live. My landlord has a lassez-faire attitude about the tree, stemming from not wanting to spend money on it and so prefers to avoid thinking much about it.

    b) Multiple certified arborists have looked at this tree and given their opinion:
    Arborist #1: Your tree is healthy (!), it's an immune reaction. Unfortunately this resulted in a one year delay in getting started doing anything about this.
    Arborist #2: Your tree has sudden oak death syndrome (!), here's some products you can buy from Amazon to treat it.
    Arborist #3: Your tree has Phytophthora cinnamoni. You should 1) water it; b) break up the hard pan under the canopy (years of dogs racing around, beating down the soil); c) mulch it, preferably with the oak leaves that fall there; d) feed it; e) pay me $600 per year to treat it with a chemical fungicide.
    Arborist #4: (this guy is a friend of the landlord, and has known the trees on this property for decades). His advice a) don't water it, this disease is a result of excess water, you're at the bottom of multiple drainage ravines and the reason the trees here get so big is because of so much water, this is the downside; b) no harm in breaking up the hardpan and mulching, but a lot of the roots are at the surface so don't turn the soil; c) feeding will make no difference; d) do you really want to treat it every year in perpetuity, with something that may or may not work? SO - this guy was pretty fatalistic, maybe the tree will make it maybe it won't. He brought us a big load of pine mulch.

    I broke up the hard pan and spread 3-4" of pine mulch. I'll continue to mulch with the oak leaves, this tree produces bushels of them in the summer. Maybe more if it's dying.

    Questions: 1) should I feed the tree with something like NPK plus minors fertilizer spikes? A neighbor told me that someone she knew fed an oak with sudden oak death, and it cured the tree. OK, maybe correlation rather than causation but if there's a chance it could help the tree I'd do it. If there's a chance it could harm it further, or feed the pathogen, I won't. 2) Is it worth treating with biological fungicides? The products I've seen that claim to be effective against Phytophtora are RootShield Plus granules (Trichoderma harzianum Rifai strain T-22 and Trichoderma virens strain G-41) and Cease, Bacillus subtilis (strain QST 713). Important - I don't have the facilities to inject the soil or the tree, or, obviously to apply as a foliar to this enormous tree. And my understanding is that the fungus is in the roots, and the canker is in the tree, so applying to the trunk wouldn't be attacking the source of the problem. Plus, arborist #4 said the bark is so thick it wouldn't get where it needs to go, and you need surfactant to penetrate. (He may have been talking about chemicals rather than bacteria.) IF these are worth a try, would applying it to the mulch under the canopy help? Would it soak in with the rains if I applied it in October or November?

    Apologies for so much background, and I realize I know nothing so some of this information / these questions may be useless.

    Want to try to save this tree, if it's possible, is the bottom line. I have some photos I can post, don't know how much help they'd be. Thanks for any help / info / insight you can give.

    https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-03-16-0408-FE
     

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