Prune in Moderation

Another reason not to prune a lot out of a tree all at once- I was working in Seattle in the upper canopy of a narrow leafed Ash (Fraxinus angustifolia) last week, and noticed the top of a number of the major limbs were no longer alive. It appeared that a huge amount of foliage had been removed by the power company a couple of years prior, exposing once shaded limbs to full sun all day long. The tops of these limbs got sunburned and died. They are now more susceptible to insect pests and diseases, potentially weakening the tree. The lesson: prune in moderation whenever possible!
As a general rule no more than 25% to 30% of the total leaf area (when leafed out) should be removed during any one year period.

Sunscald on an Ash branch from sudden exposure to day-long sun.

Sunscald on an Ash branch from sudden exposure to day-long sun.

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Trunk decay

I came across something interesting last week while removing a small cypress tree in the Madison Valley of Seattle. The tree had a lot of recent branch and foliage die-back and generally was not looking robust.
When I made the final cut low on the trunk I noticed a fair amount of decay (notice the spongy looking parts of the trunk in the photo on the left). What I found interesting were the narrow bands of white fungal mycelium that were visible in the bark. They seemed to be only in the areas directly adjacent to the sections of rot further in the trunk. Perhaps the fungus decaying the wood is also visible in the otherwise healthy looking outer bark?
I think a very close look at the bark layers (without removing the tree or even damaging the trunk) would have indicated the internal decay. Something I made a note of in case I come across a similar looking cypress tree in the future.
To know if the two observations are actually correlated one would have to identify the fungal species, likely quite difficult since it wasn’t fruiting.

This tree had limited areas of healthy xylem and cambium, some of which can be seen in the upper left side of the trunk.

This tree had limited areas of healthy xylem and cambium, some of which can be seen in the upper left side of the trunk.


Note the bands of mycelium in the outer layers of bark.

Note the bands of mycelium in the outer layers of bark.

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Mulch Around Trees

Adding wood chip mulch around young trees is one of the best things one can do to assure their success. As I’ve mentioned in previous posts, wood chips have a number of benefits. From moderating soil temperature, holding moisture through our dry summers, preventing erosion, to inhibiting weed growth, and eventually decomposing to help build healthy soil.
Another function they can serve is to prevent damage to surface roots. The birch tree pictured below looks like it was a victim of an unknowing “mow and blow” landscaping crew. These are the landscape crews that keep a lot of yards looking clean and tidy with straight edges and rounded bushes. One of the main tools in their arsenal is the leaf blower. Besides the noise and air pollution, there’s another reason the use of these machines should be limited in the landscape- soil erosion. Leaf blowers can create wind speeds from 140 to 270 mph (according to Wikipedia), easily strong enough to blow loose soil particles away. I’ve watched numerous landscape crews around Seattle remove weeds (either by hand or with tools) then come through to blow away leaves and other debris with a leaf blower. As the leaves are getting blown away, loosened soil particles are as well.

Exposed and damaged roots.

Exposed and damaged roots.


Anyway, back to my photo of the birch tree: repeated soil disturbance and leaf blower usage around the base of this tree has likely lowered the soil level, allowing the roots to be exposed and then damaged by other lawn care equipment. These are likely the structural roots of the tree, the roots that the tree needs for the rest of its life to physically hold it in place. Placing mulch (preferably woodchips, not bark) around the base of trees, but not against the trunk, prevents a lot of potential problems, and benefits the tree in innumerable ways.
So get out there and mulch in preparation for our dry summer!
The exposed roots covered with a protective layer of wood chip mulch.

The exposed roots covered with a protective layer of wood chip mulch.

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Plum blossoms

It’s flowering time for the plums here in the Seattle area, specifically the Asian type of plum (the European types bloom later). Pruning on these trees can also begin in the next couple of weeks. There are less fungal spores in the air that might infect pruning cuts, and the trees are out of dormancy and able to respond to these small wounds. Shortening some of those really long horizontal branches that can sometimes break at the end of the summer when they’re laden with fruit, might be a good idea. Also, thinning thick areas of the canopy to increase airflow and sunlight helps increase fruit quality. If you’re not feeling confident in your pruning skills, give me a call to schedule a lesson.
Pruning Instruction
Plum blossoms

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Weeping Larch

Larches are a type of conifer that lose their leaves (needles) for the winter. This sometimes causes people not aware of what they are to think they are dying, despite this being a completely normal process.
Larix species are native to portions of Washington state, among other places. There are a number of species and varieties, including this small weeping one I recently pruned.

This weeping larch hadn't been pruned (besides "skirting" the bottom) for at least 5 years. Lots of deadwood make the structure hard to see even during the winter after it has dropped its needles.

This weeping larch hadn’t been pruned (besides “skirting” the bottom) for at least 5 years. Lots of deadwood make the structure hard to see even during the winter after it has dropped its needles.

After removing the deadwood, and selectively thinning some of the live branches in the thicker areas.

After removing the deadwood, and selectively thinning some of the live branches in the thicker areas.

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Autumn Olive

Autumn Olive Autumn Olive. An interesting and useful plant for your landscape. It produces small red or orange berries late in the summer that are a great snack right off the bush. They’re high in a number of the same beneficial nutrients found in tomatoes, but in much higher concentrations. Elaeagnus umbellata also fixed nitrogen into the soil, so it can help rebuild soils or be planted near trees that will eventually outgrow it, adding nitrogen to the root zone of the long lived tree. Autumn Olive grows up to about 12 feet tall in most sites. Another very similar fruit is Goumi (Elaeagnus multiflora). There is a fair amount of confusion between the two, especially online.

I took this photo of Autumn Olive in bloom at the end of march in the Skagit Valley.

I took this photo of Autumn Olive in bloom at the end of march in the Skagit Valley.

Caution is advised, as some say both species can become invasive via bird spread seeds. Although I haven’t seen this occur in my experience, nor have I heard this from fellow gardeners in the Pacific Northwest.

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Pear Trellis Rust

Pear trellis rust (Gymnosporangium sabinae) is an interesting fungus in that it requires two entirely different plant hosts to complete its life cycle – pear and juniper. Spores produced on junipers only infect pears, and those produced on pear only infect juniper. It gets its name from the fruiting structures on the underside of the pear leaves- they look a bit like a trellis when examined under a magnifying lens. The symptoms on pear generally only effect the leaves. Starting as small bright orange spots in the spring and gradually turning into thick growths later in the summer as they release spores. It’s a relative newcomer to our area. It was found on pear trees in Bellingham in 1997. Previously known only from Southern California and Southern British Columbia, it has now spread throughout most of Western Washington and is a fairly common sight in Seattle.

2014-10-04 18.53.26

Here are some non-chemical control suggestions from WSU:
-Prune out swellings or galls from junipers.
-Remove and destroy infected material from pear trees (fallen leaves, mummified fruit, heavily infected twigs, etc.) to help minimize disease spread. To help protect junipers, infected plant material must be removed from the pear trees before spores form, usually around late August in western Washington. This may not be practical on large trees.
-Plant only disease-resistant junipers in areas where this disease is a concern; cultivars of Juniperus squamata, J. horizontalis, and J. communis are resistant.
-Do not plant pears and junipers within 1,000 feet of each other. Most local transmission of this disease is by wind-blown spores.
-Complete removal of one host is the only completely effective cultural control.
-Carefully examine plants before adding them to your landscape. Many diseases are introduced on infected planting material.
 

This is from the ministry of Agriculture in B.C.
-Plant junipers and pears as far away from one another as possible. Consider your neighbor’s plants, as well as your own. If the two hosts are separated by at least 150 meters [~500ft], there will be minimal damage to the pears.
-If infected pear and juniper are in close proximity, consider removing one or the other. Don’t leave juniper brush piled in your yard as the fungus will sporulate on it and spread to the pears.
-To prevent spread of the disease from your pear tree to nearby junipers, pick the infected leaves before mid-August each year, if they are not too numerous. No special disposal of these leaves is required. The fungus will die out in a few days when the leaves shrivel up.
-Prune out any gall-like growths at the base of twigs on pear.
-Avoid planting ornamental pears. They are also susceptible to the disease.
-If selecting junipers for a landscape containing pears, select resistant juniper species, including Juniperus horizontalis, J. communis and J. squamata, or choose a different type of conifer.
Also from the ministry of Agriculture, B.C.:
-Symptoms on juniper are much less obvious. They can only be seen during wet weather in April and early May. At that time, orange, jelly like masses (telia) swell and enlarge on infected juniper branches. Telia release release spores which are capable of infecting nearby pear leaves which are just starting to grow. After the spores are released, the telia shrink and dry up, and infection on juniper remains dormant until the next spring. Infected junipers continue to grow and appear healthy. Some varieties may develop spindle-shaped swellings on the branches.
 

The fruiting structures can be seen protruding from on the underside of these infected leaves, in this photo courtesy of Jeremy Harrison-Smith. The initial infection is often bright orange, sometimes darkening to red late in the summer.

The fruiting structures can be seen protruding from on the underside of these infected leaves, in this photo courtesy of Jeremy Harrison-Smith. The initial infection is often bright orange, sometimes darkening to red late in the summer.

It seems the consensus is that the only sure way of eradicating the fungus is to take out any junipers near your pear. 300-500ft some sources say, To 1,000ft (the most commonly stated number). This is fairly impractical for a city neighborhood situation like most of Seattle, but the further away an infected neighboring juniper is the less likely spores from it will land on your pear. So if there’s a juniper directly next door, perhaps some discussion with the neighbor about its replacement could happen as there are resistant varieties, and (in my opinion) much more interesting plants that could replace it. In general keeping the pear tree as happy as possible will be of benefit. Putting down a wood chip (not bark) mulch under the tree will help build the soil, moderate soil temperature and retain moisture. Making sure it has sufficient water during the drought time at the end of the summers will also help. Don’t use overhead sprinklers, as the fungus needs water to infect the leaves.
 

Sources:
http://www.ladybug.uconn.edu/factsheets/documents/pear_rust.html

http://www.agf.gov.bc.ca/cropprot/peartrellis.htm

-Pear (Pyrus spp.)-Trellis Rust In: Pscheidt, J.W., and Ocamb, C.M., senior editors. 2014. Pacific Northwest Plant Disease Management Handbook [online]. Corvallis, OR: Oregon State University. http://pnwhandbooks.org/plantdisease/pear-pyrus-spp-trellis-rust (accessed 4 December 2014).

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Mulching

Anytime is a good time to mulch your landscape, but fall is especially great. Covering bare soil before we get heavy fall rains and adding another few inches around the trees you mulched last year will really pay off next summer.

A pile of freshly chipped maple.

A pile of freshly chipped maple.


Mulch moderates soil temperature, retains moisture, inhibits erosion and weeds, and feeds the soil food chain. All this allows a longer growing season, reduces summer waterings, helps root growth during the winter, and much more.
I’m referring to what some call arborist chips, not the beauty bark or cedar “play chips” that are sold at nursery supply places. Woodchips hold water and break down relatively quickly whereas bark is naturally hydrophobic (it repels water, not helping much in the dry summer) and takes many years to turn into soil.
So get out there and mulch your landscape! Calling large tree removal companies or signing up for a service I recently became aware of (chipdrop) are two solid options for acquiring woodchips. I’m also now selling pickup truck loads of chips in the Seattle area. Contact me if you’re interested.
Some more information on woodchips from WSU and Linda Chalker-Scott: Arborist Wood Chip Mulches – Landscape Boon or Bane?
See also: The Myth of Pretty Mulch

Posted in Landscapes, Tree Care | 1 Comment

Quince Leaf Blight

Quince trees seem to be one of the least common fruit trees in Seattle, and Western Washington in general. This is unfortunate because they can be made into some delicious jams and sauces. If you’re fortunate enough to have a quince tree in your yard, there’s a chance your tree has quince leaf blight. This is a fungal infection (like nearly all leaf blights) that shows up as brown spots on the leaves and sometimes the fruit.
Quince Leave Spot The PNW Plant Disease Handbook from Oregon State University sums up the life-cycle: “The fungus overwinters in diseased leaves and shoots. Cool, wet weather favors disease development in the spring. Spores are disseminated by splashing water and need 8 to 12 hours of leaf wetness to infect leaves. Susceptibility does not seem to be reduced with leaf maturity.”
The fungus (Diplocarpon mespili) can infect other members of the Roseaceae family such as Asian pears, hawthorn, pear, photinia and serviceberry, but the symptoms are usually not as severe.
Like most fungal infections keeping the orchard tidy is one of the best ways to keep the disease in check. Raking up and disposing (not composting) the fallen leaves and any infected branch tips or fruit will reduce the re-infection rates the next spring. Don’t irrigate with overhead sprinklers because the fungus needs water to infect leaves. A copper based fungicide may speed recovery, but often good orchard hygiene will keep the disease in check.

 
Sources:
-Pscheidt, J.W., and Ocamb, C.M., senior editors. 2014. Pacific Northwest Plant Disease Management Handbook [online]. Corvallis, OR: Oregon State University. http://pnwhandbooks.org/plantdisease (accessed 22 Sept. 2014).
-Ashridge Nurseries, http://www.ashridgetrees.co.uk/hedging-trees-fruit-questions/hedging-fruit-tree-diseases/quince-leaf-blight. (accessed 22 Sept. 2014)
 

Looking up into a healthy quince tree loaded with fruit.  Quince are ready to harvest when they turn yellow, loose most of the fuzz on their skin, and come off the tree easily.

Looking up into a healthy quince tree loaded with fruit. Quince are ready to harvest when they turn yellow, loose most of the fuzz on their skin, and come off the tree easily.

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Cherry Bark Tortrix

The Cherry bark tortrix is a pest on trees and shrubs of the rose family (Rosaceae). This means most common fruit trees have the potential to be affected including apple, cherry, plum, and peach. It’s a relatively new pest to Washington state having arrived here in the early 90’s. Damage is caused by the larvae of the moth Enarmonia formosana. Eggs are laid singly by adult moths on the bark of susceptible species. After hatching they burrow through the bark and begin to eat the cambium. This damage to the part of the tree that transports water and nutrients decreases the tree’s vigor. Decreased vigor and the wounds caused by the larva can make the tree more susceptible to other diseases or fungi. An excellent indication of whether there’s an infestation in a particular tree are frass tubes and (to a lesser extent) frass, which are small pellets of insect excrement- see photos.

A few individual frass tubes can be seen at the base of this cherry.

A few individual frass tubes can be seen at the base of this cherry.

Control options are limited. It’s only practical to attempt to control the insect in its larval stage as the flying time for the moth can extend from April to September. Cherry bark tortrix (CBT) prefer to attack stressed or damaged trees and also appear to attack Mount Fuji Oriental and Weeping (or Higan) Flowering cherries especially hard. Some things that can be done to help control this pest are to conserve parasitic wasps and other predators by reducing or eliminating pesticide usage and avoiding any mechanical injuries or large pruning cuts, as this provides easy access into the tree. There are a number of parasitic wasps that will parasitize CBT eggs and larvae. So it stands to reason that growing plants nearby that benefit these wasps will help control CBT. These parasitoid wasps prefer plants that have small flowers and are rich in nectar such as dill, yarrow, mustard, fennel- umbels and asters in general.

A relatively unusual sighting of the larvae of cherry bark tortrix. Take note of all the frass pellets.  I took this photo in North Seattle in late May.  The larvae are about 1cm in length.

A relatively unusual sighting of the larvae of cherry bark tortrix. Take note of all the frass pellets. I took this photo in North Seattle in late May. The larvae are about 1cm in length.


Trees may be able to survive for years with small infestations and eventually overcome them. When infestation is first noticed, remove any loose bark and cocoons in the spring, and remove and destroy heavily infested branches or trees. Pheromone traps are available for monitoring CBT and may also provide some control if deployed in sufficient numbers. There are a few approved pesticides for the homeowner, but they are only approved for use on ornamental trees. See the WSU hortsense website for more information.
 
 
 
 

Sources:
http://pep.wsu.edu/hortsense/ found under- tree fruits; cherry.
http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=570
http://puyallup.wsu.edu/plantclinic/resources/pdf/pls67cherrybarktortrix.pdf
http://www.seattle.gov/util/groups/public/@spu/@conservation/documents/webcontent/COS_005341.pdf
Edible Forest Gardens Vol. 2 D. Jacke and E. Toensmeier. pg 579

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