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.
Is this Armillaria mellea, the dreaded oak root rot fungus? I really do not know. All the elements are here. The stump is that of a coast live oak. Bellow the stump there are the remains of roots. Those necrotic roots are undoubtedly decomposing as a result of rot. That rot is undoubtedly associated with this fungus. Furthermore, it fits the description of oak root rot fungus. The toasted spots were probably caused by weathering as the mushrooms started to develop while the weather was still warm and dry.
Now that the soil and rotting wood are damp from rain, this fungus is really proliferating. The individual mushrooms within the soccer ball sized mass were only about as big as those at the lower left margin of the picture just prior to the rain. They do not last long, and might become gooey black slop after only a few sunny days. The stump may continue to rot for a few more years. It is out of the way, so there is not need to get rid of it.
It annoys me when landscape professionals tell me that a particular spot in the region has oak root rot fungus. Of course it does. It is everywhere. It is quite natural here.
Oak root rot fungus is justifiably dreaded. It can easily kill the most majestic oaks that have survived for centuries.
However, most of the problems with oak root rot fungus in landscape situations are caused by supplemental irrigation and other gardening techniques. Oaks that have survived on natural seasonal rainfall for centuries are much more susceptible to rot if their roots are kept continually moist by the irrigation needed to sustain other plants added around them. Roots that get severed for the installation of pavement or building foundations are likewise much more susceptible to rot, particularly in spots where drainage from roofs or paved surfaces enhances soil moisture.
For this particular pathogen, gardening is more often the problem.
It is as scary as it sounds. Well foliated limbs or entire trees really do fall spontaneously during the calmest of warm weather. It never fails to frighten anyone who witnesses it. Those who witness it always express the same difficulty with trying to explain it to those who did not witness it, as if they know that no one will believe them.
Several people heard this cottonwood limb fall onto a bridle path in Felton Covered Bridge Park. It is not a particularly large limb. The diameter about a foot above the flared union is only about seven inches.
Yet, even this relatively small limb is seriously dangerous when it falls from above, and from such a height.
A much larger sycamore limb that was almost two feet in diameter fell nearby a few years ago. It was like a full sized tree falling from the sky!
What makes it so frightening is the spontaneity. We expect limbs to break when the wind is blowing. Trees are more likely to fall when the soil is saturated from an abundance of rain. Dynamic weather like wind, rain and snow are expected to be the cause of limb or tree failure. Passive weather like warmth and humidity seem like they should be innocent of causing such damage. Not so.
Warmth accelerates vascular activity, which increases the weight of healthy foliage.
Humidity inhibits evapotranspiration (evaporation from foliar surfaces) that would otherwise decrease the increasing foliar weight.
Breezes that are normally thought of as a cause of limb failure would actually enhance evapotranspiration. Therefore, a lack of any breeze actually increases the potential for spontaneous limb failure.
So, while the weather is warm, humid and still, just when you least expect it, spontaneous limb failure is most likely to happen.
This unhappy native white alder, Alnus rhombifolia, had been deteriorating for quite a while. White alders do not last long even in the wild. A few nearby have already been removed. This one is next. They were nice and shady when the landscape was new. Nicely maturing sycamores and a bigleaf maple can take over for this one now.
As bad as it looks, this nasty stain had nothing to do with the imminent doom of this tree. It developed only recently, and very quickly. It is not nearly as bad as it looks. If the tree were not to be removed, it could survive with this problem for quite a while. Other healthier trees can live with it for many years or indefinitely, and some actually recover.
It is ‘flux’. More specifically, it is slime flux, which is also known as bacterial wetwood. The obvious symptoms are this unsightly bleeding and staining. A less obvious symptom is the swelling that caused the fissure in the bark from which the unsightly fluid is draining. The fluid can smell nasty!
Furrows in the bark develop naturally as the trunk expands over many years. They do not penetrate through the bark into the cambium below.
Fissures are fractures that penetrate through the bark and into the cambium. The fissure in these pictures developed so recently that the orange interior of the bark has not oxidized to tan or gray yet. The fissure is about six inches long, and slightly lower than a doorknob.
Even for healthy trees, there is no remedy for slime flux infection. It can only be left to do whatever is going to do. It can accelerate internal decay, but is otherwise not as detrimental to the health of an infected tree as it would seem to be.
(The article from my weekly gardening column that is typically posted on Thursday was posted yesterday, which is why this article, which is more appropriate for Wednesday is posted today.)
The ivy in this sycamore did not just climb up from the ground to hang over this big limb. If you look closely, you will see no vine coming up from the ground. This small patch of ivy as well as a small pyracantha, are growing in a decayed cavity on top of the big limb. The ivy may have climbed up a long time ago, and then rooted into the cavity before the original vine was somehow removed. Alternatively, the ivy might have grown from a seed that was dropped by a bird or ivy vines that are higher up in nearby box elder trees. It is impossible to say now.It is also difficult to say why there is such a large cavity on top of the limb. It could have originated as a large scar incurred from the impact of another large limb that fell from above. There are a few cavities higher up that were caused by large limbs breaking away. Although unlikely, the cavity could have developed from sun scald damage, after the upper surface of the big limb suddenly became exposed by the loss of limbs higher up.This other aerial patch of ivy hangs from a smaller cavity higher in the same tree. Oddly, among sycamores, such cavities on upper surfaces of large limbs are not uncommon. Sycamores often drop large limbs from high in their canopies, exposing or damaging lower limbs below. Their lightly colored bark is very susceptible to sun scald if suddenly exposed after always being shaded. It is also not very resilient to heavy impact. Of course, more typical cavities develop on trunks where significant limbs broke or were pruned away. Other plants can grow in these as well, as demonstrated by the ‘epiphyte’. https://tonytomeo.wordpress.com/2017/11/15/epiphyte/
The two pictures above, although not relevant to any symptoms, are important to our Community because the historic Felton Covered Bridge just got a new roof! (https://tonytomeo.wordpress.com/2017/12/02/felton-covered-bridge/) Dead box elders that are already starting to destabilize and collapse are now leaning onto the edge of the new shingles! They really need to be removed before winter storms move them around, and they dislodge any shingles.
The first of the two pictures below show basidiocarps associated with fungal decay of the trunks and roots. This decay destabilized and compromised the structural integrity of the necrotic trees with remarkably efficiency. The trees died only last spring, and are already collapsing! The second of the two pictures below simply shows decaying bark peeling from a necrotic trunk.
This all happened so suddenly. Like SODS (Sudden Oak Death Syndrome) it is likely to be misdiagnosed a few times before the primary pathogen is actually identified. Also like SODS, it may be ignored as an isolated situation affecting a few trees that are not very popular anyway. When SODS first started killing a few of the unpopular tanoaks, it did not seem like much of a problem. It did not get much attention until it started taking out majestic coast live oaks that had been healthy for centuries.
The two pictures below show a cross section of a necrotic trunk that needed to be cleared from a bridle trail. Galleries have been excavated by the larvae of unidentified boring insects. The second picture is merely a closeup of the first.