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?

The Humongous Fungus Among Us

04Is 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.

Fireblight Kills Pears And Apples

61005thumbBunches of blackened leaves hanging from blackened stems in otherwise healthy pear trees really are as serious as they look. They probably appeared as new growth was developing in spring, and are still as dead now as they were then. As surrounding foliage colors and falls, the blackened foliage will remain until it gets knocked out by rain and wind in winter, or until it gets pruned out.

Because these dead bits seem to have been scorched by fire, the bacterial infection that causes them is known as ‘fireblight’. Pear, flowering pear and evergreen pear are most susceptible to it. Apple, flowering crabapple, quince, flowering quince, hawthorn, loquat, cotoneaster, pyracantha and photinia are also very susceptible. Some cultivars are more resistant to fireblight than others. Few other members of the ‘rose family’ are rarely infected.

At the base of each dead bit (or toward the supporting limb from dead bits that do not stand upright) is a lesion where the bacteria that cause fireblight infected the stem. These infections not only obstruct vascular activity and kill the distal (outward) portion of the infected stems, but they also spread proximally (inward) to more important limbs, branch unions and even main trunks and roots.

Fireblight is transmitted mostly by bees, and also by other insects, birds, rain and wind, while trees are blooming in spring. It most often infects through flowers, and can also infect where infected debris, particularly falling flower parts, get caught in branch unions. If it infects root suckers, it can infect the roots right away, and kill an entire tree. Root suckers should be pruned away anyway.

There is no remedy for fireblight. Because it is very contagious, all infection should be pruned out. Because infection extends inward from obvious lesions, infected stems should be pruned back at least a foot and a half below (inward from) obvious infection. Sadly, this often disfigures infected trees, sometimes severely. Pruning scraps should be removed from around susceptible trees.

Some say that fireblight should be pruned out in summer. Others say that winter is best. Really though, the only bad time is spring, while weather is warm but still damp, and the trees that are so susceptible to fireblight are active and blooming. The reason for pruning it out in winter is that the disease is inactive while cold. However, it does not get cold enough here to slow it down much.


P80523This 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.P80523+P80523++

(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.)

Dead Box Elder Update

P71223P71223+What is killing the box elders? ( I still do not know. I know that does not sound like much of an update. All I can share is some pictures of secondary symptoms observed now that the affected trees are deteriorating.

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! ( 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.P71223++P71223+++

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.P71223++++P71223+++++

What Is Killing The Box Elders?

P71004Remember our concern about the mistletoe? ( You might think that everyone would be pleased to see it gone. Yet, there is the concern that whatever killed the mistletoe might kill something else. That is what happened when the SODS killed so many coast live oaks after being ignored for a long time in the tan oaks. We were aware that the tan oaks were dying, but because the trees were so unpopular, we were not too concerned about it.

Now the box elders are dying around Felton. It is hard to say how widespread the problem is because it has not been investigated yet. Like tan oaks and mistletoe, the native box elders are not exactly popular trees. They do not even make good firewood. We only use them as firewood to get rid of them. However, when so many are die, it leaves big holes in the forest canopy. This is not really a problem, since the forest will have no problem filling the holes in, but it certainly gets our attention. Will the disease or insect pathogen that killed the box elders kill something else next?

The trees seemed healthy as they defoliated last autumn. They were bare through winter when the San Lorenzo River came up higher than it had since 1982. A few box elders got taken away by the River, along with all sorts of other riparian trees from the flood zone, but that is to be expected. Then, after the River receded, many box elders that were in the flood zone did not foliate in the spring. A few foliated, only to have their new foliage shrivel and die shortly afterward. Some of the dead trees became infested with boring beetles. All of the dead trees deteriorated rapidly through summer, and some have dropped big limbs or fallen over.

What is happening with the box elders could be completely normal, and caused by an endemic pathogen; but it makes one wonder. There are so many new insects and diseases being brought in with plants arriving from all over the world, without any regulations to limit the spread of such insects and diseases.P71004+