P00202
Flagging (sudden necrosis of distal foliage) used to indicate the beginning of a sudden end.

Phytophthora ramorum is the pathogen that initiates Sudden Oak Death Syndrome, which is known simply as SODS. Monarthrum scutellare, which are known as ambrosia beetles, and are the secondary pathogen associated with the syndrome, infest and kill tanoak and coast live oak that are infested with Phytophthora ramorum, about as quickly as symptoms are observable.

Hypoxylon thouarsianum is a tertiary but merely opportunistic pathogen associated with the syndrome. By the time it gets established within galleries excavated by the ambrosia beetles, the affected trees are almost completely necrotic. That first ‘S’ in SODS is there for a reason. It is an efficient process. Death occurs too suddenly for affected trees to drop any of their leaves!

Each of these three pathogens causes distinct symptoms. Phytophthora ramorum causes trees to bleed black tar-like fluid, and causes tanoak to exhibit foliar flagging as seen in the picture above. Monarthrum scutellare expels finely textured frass from the galleries it excavates into infected trees. Hypoxylon thouarsianum produces distinct small and black fruiting structures.

In the past several years though, Sudden Oak Death Syndrome has often been a bit less than sudden. There are a few tanoaks here that have exhibited foliar flagging for a few consecutive years, without any bleeding from the trunk or infestation by ambrosia beetle. Some coast live oaks have exhibited minor bleeding, but likewise have not become infested by ambrosia beetle.

It is as if the ambrosia beetle is no longer proliferating as it had been. It actually seems to be rather scarce. Trees that were expected to succumb suddenly to ambrosia beetle infestation are succumbing slower to infestation of only Phytophthora ramorum. The process is variable, so might have potential to kill some trees rather suddenly, but may take a few years to kill others.

Could some possibly survive?

4 thoughts on “SODS?

    1. SODS is a sore subject for me. It is a very long story. I am not convinced that it is a new set of pathogens here. All three could be native. This epidemic effect could be the result of disruption of the local ecology. It could be a completely natural process that happens every few centuries or so. Like so many other epidemic diseases in the forests here, it could be the result of fire suppression, which deprives the forest of burning. I am dismayed that with all the research that went into it, no one really knows how or why it happened, or how and why it is not as serious of a problem as it was.

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    1. I doubt that this is the first time this disease came through here. I believe that it is a consequence of the disruption of ecology, just like the diseases that too out all the Monterey pines so many years ago. Once all the geriatric pines (that were not culled by forest fire) dies out, new ones started the process over. The diseases are still out there, but do not proliferate as badly in the younger forests.

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