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Elisabeth C. Miller Library

Keyword: Trees--Diseases and pests

Fraser fir with rusty tips

We planted a young Fraser fir last March. It has a lot of
new growth, but has developed some dead-looking tips here and there that
are a reddish rust color. I am wondering if we have a serious problem or
should I just remove the affected tips and not worry about it? I have
noticed a lot of trees this summer on my travels out through the
Cumberland-Enumclaw area that look a similar cinnamon color and are
totally dead!

 

The problem you describe could be the result of drought injury, or it
could be one of several rust and fungal diseases which affect fir trees.
Was the tree watered well after planting? Here is information
on drought injury from Oregon State University’s plant disease database. Excerpt:

Drought injury usually progresses from the top of the tree downward and
from the outside to the inside of the crown. Top dieback and branch death
may be common. Defoliation of the mid-crown or loss of needles at the
base and tip of shoots can also occur in Douglas-fir. Older needles
commonly turn yellow and are shed prematurely. Roots may be alive even
though the entire above-ground parts are dead. Winter injury, gopher and
root weevil problems can produce similar symptoms.

Your description also sounds like the symptoms of Phytophthora, a fungal
disease which is common in our area. Excerpt:

Phytophthora root rot is usually a problem only in areas with poor
drainage or where flooding occurs. The fungus attacks the roots, which
rot and die. The infection moves up into the crown, where the cambium
(soft inner bark) turns reddish-brown or caramel in color instead of the
normal white to greenish color. Older trees may develop cankers on the
trunk, which are a dark reddish-brown when cut. The cankers may be
accompanied by split bark and oozing pitch. Lower branches wilt, turn
dark red, and die back. Younger trees are often killed outright, while
infected mature trees may show wilting, branch dieback, and/or gradual
decline.

Missouri Botanical Garden’s Integrated Pest Management site has information and includes an image of Fraser fir suffering from Phytophthora.

The Pacific Northwest Pest Management handbooks have a section on diagnosing and controlling phytophthora diseases.

I recommend taking a sample of one of the cinnamon-colored branches to a
Master Gardener Clinic, and also taking photos of the whole tree, so that
you can have the problem diagnosed. If you are near Enumclaw, the Pierce County Master Gardeners offer diagnostic clinics.

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Managing hemlock woolly adelgid

My Western Hemlock is infested with woolly adelgid. Help! How can I save my tree?

 

The USDA Forest Service website
includes information on different ways of managing the Hemlock woolly adelgid.

The most effective approach is prevention, as treatment tends to be expensive
and is not always effective. Information from University of Maryland Extension does describe the use of dormant oil spray in late winter and summer application of horticultural oil and
insecticidal soap, but care must be taken to cover the entire tree. Also, it is
important to avoid the use of nitrogen-heavy fertilizers which create a lot of
succulent new growth attractive to the pest.

I recommend that you consult a certified arborist for advice on how to save your <em?Tsuga heterophylla (Western hemlock). You can obtain
referrals from Plant Amnesty or you can select an arborist from the directory of the Pacific Northwest Chapter of the International
Society of Arboriculture.

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Decline of the Pacific Madrone

Multiple .pdf files of the publication from the proceedings of the 1995 symposium held at the Center for Urban Horticulture on the Pacific Madrone.

Controlling mountain pine beetles

What is the latest method of eradication for the mountain pine beetle, Dendroctonus ponderosae, that is rampant in western Canada?

 

In the northwestern U.S., USDA Forest Service states that the focus has shifted from using pesticides to taking preventive measures:
Excerpt:
Control methods have shifted away from direct control (e.g. spraying, felling, burning) and towards prevention of outbreaks. This course of action was chosen after thoroughly exploring direct control measures for nearly a century and arriving at a simple conclusion: They don’t work. It is possible to prevent infestation with penetrating sprays on individual, high value trees such as those in campgrounds and near houses, but they need to be applied before the tree is infected and the cost of such treatments is prohibitive for any large-scale application.

Once a mountain pine beetle outbreak begins to spread, it can be stopped by thinning the stand ahead of the edge of the outbreak. This is because outbreaks expand on a tree to tree basis where the incoming beetles switch their attacks from a recently attacked-stem to the next largest tree. More importantly, infestations can be prevented by thinning stands before crown closure, an operation that not only increases the vigor of the residual stand, but also prevents the spread of an outbreak if individual trees have been attacked.

Mountain pine beetles are a natural part of western ecosystems, and for this reason will never be completely eradicated (nor should they be, as they serve to create small stand openings which are important for biodiversity of both flora and fauna). As such, the death of a few trees on your property doesn’t necessarily mean an epidemic is getting started; check your trees for root disease symptoms. To maintain mountain pine beetles at their normal levels, predisposing factors for outbreak must be removed. Some of these, such as environmental stresses, are not possible to control. However, many stresses are related to stand management practices. First and foremost, two situations need to be addressed: root disease centers and overstocked stands. More details about treatment for root disease centers have been given in other WSU Cooperative Extension “Forest Health Notes;” in summary, they need to be identified and planted with resistant species. Overstocking causes trees to compete for water, light and nutrients, and thus weakens their defenses against bark beetle attack. To minimize stand stresses and maintain vigorous growing conditions, stand managers should: (adapted from Berryman: Forest Insects, 1986).

Natural Resources Canada has a task force on the mountain pine beetle. You might want to contact them for the latest update. Go to their mountain pine beetle website and follow the links for additional information, including how to contact CCoFI.

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lack of flowering on Magnolia grandiflora

I have a
very tall, well-established Magnolia grandiflora. The tree is located on
the southeast corner of the lot. Every summer it has produced large white
flowers, but last summer that there weren’t as many blooms, almost
none. It’s left alone and watered spring through summer by a sprinkler system. I have also noticed yellowing of the leaves at the ends of the branches. Usually the leaves
have been dark and green. I’m wondering if it is a lack of nitrogen or food of some sort.

 

There are a number of reasons that plants may fail to flower, and it
would be difficult to pinpoint precisely why the Magnolia made such a
weak show this past summer. Sometimes, cold temperatures kill off flower
buds (and there were some cold snaps last winter). The tree is not
immature, and it sounds as if it is not pruned improperly, so those
potential causes can be excluded. You also indicate that it is not
fertilized, so it is probably not receiving excessive nitrogen which can
lead to lots of leafy growth at the expense of flowers. I wonder if
anything else in its environment has changed: has the amount of light
changed (any new construction obstructing sun?), or has anything happened
to the soil where it is planted? You might wait and see if flowering
returns to normal this year.

As for the yellowed leaves, that might be a result of winter injury
(desiccation) or drought stress. However, yellow leaves can also be a
symptom of sunburn or lack of light, or nutrient deficiency. See the
link here to University of California, Davis’s page on Magnolia problems. Excerpt:

Mineral deficiencies:
Certain nutrients, in relatively small amounts, are required for healthy
plant growth. Deficiencies can cause tip chlorosis or necrosis or cause
foliage to discolor, fade, distort, or become spotted, sometimes in a
characteristic pattern that can be recognized to identify the cause.
Fewer leaves, flowers, and fruit may be produced, and these can develop
later than normal and remain undersized. More severely deficient plants
become stunted and exhibit dieback. Commercial laboratories can conduct
foliage tests or soil analysis to verify deficiencies.

Identification/Solutions:

Nitrogen and iron are the only nutrients in which woody landscape plants
are commonly deficient. Poor root growth caused by water-logged soil,
root diseases, and nematodes can also cause iron deficiency symptoms.
Fertilize only as needed and only if other problems have been eliminated
as the cause of poor growth. Avoid overfertilization, especially with
high-nitrogen fertilizers. Slow-release formulations of nitrogen or
organic fertilizers reduce some risk of overfertilization. Correcting
deficiencies of minerals is tricky. Apply only the mineral found to be
deficient. In some cases, soil characteristics may exacerbate
deficiencies. Alkaline soil (high pH) often makes iron or manganese less
available; reducing alkalinity with sulfur or organic amendments (peat
moss) may be all that is needed. Some minerals such as iron, manganese,
and zinc are absorbed more rapidly as a foliar spray than a soil
application.

If the environmental causes don’t ring true with your tree’s situation,
you may want to do a soil test to see if there are nutrients which need
to be supplemented.

dogwood disease and coppicing smoke tree

Can you give me some general information about Dogwoods and anthracnose? Also, I would like to know about coppicing Cotinus coggygria.

 

Here is information about dogwoods and anthracnose from University of Massachusetts-Amherst.

Washington State University’s HortSense website has a factsheet on anthracnose for home gardeners which recommends the following:

  • Plant species which are anthracnose-resistant. Dogwoods showing very good resistance include: C. kousa ‘Beni Fuji’, C. kousa ‘China Girl’, C. kousa ‘Lance Leaf’, C. kousa ‘Milky Way’, C. kousa ‘Porlock’, C. kousa ‘Silver Cup’, C. kousa ‘Snow Bird’, C. kousa ‘Speciosa’, C. kousa ‘Summer Majesty’, C. kousa ‘Tsukabo-no-nine’, C. kousa ‘Wilton’, C. kousa ‘Dwarf Pink’, C. kousa ‘Ed Mezett’, C. kousa ‘Satomi’, C. florida hybrids, C. florida ‘Spring Grove’, C. florida ‘Sunset’, C. racemosa, C. canadensis, C. mas, C. alba, C. alternifola, C. sericea, and C. sericea ‘Flaviramea’.
  • Where practical, prune and destroy infected twigs to prevent overwintering of the disease.
  • Rake and destroy all fallen leaves, both during the summer and in the fall.
  • Do not compost diseased materials.

Oregon State University Extension’s Online Guide to Plant Disease Control (aimed at professional horticulturists) provides a corroborating list of cultural controls for Anthracnose and adds an extensive list of chemical controls. It’s always best to use cultural controls and avoid chemical ones if you can.

Some dogwoods in the Pacific Northwest have been known to recover from anthracnose, according to Douglas Justice of University of British Columbia Botanical Garden.

The Royal Horticultural Society has useful general information on coppicing, and includes Cotinus coggygria (smoke tree) among those plants which respond well to this pruning technique.

Betula jacquemontii and their susceptibility to pests

I am a professional landscaper in the Portland area. I am wondering if Betula jacquemontii have much of a problem with aphids or other pests. Everything I read says they do, but since this tree is one of the Great Plant Picks, I wonder if that’s not the case.

There is certainly the potential for aphids with this type of birch. I don’t think all the plants listed in Great Plant Picks are necessarily immune to problems, more that they can serve a particular purpose in the landscape. Betula utilis var. jacquemontii is also susceptible to bronze birch borer, according to Oregon State University.

University of British Columbia Botanical Garden Forums includes a discussion of the merits (or not) of this tree, including this comment from Seattle-area gardening expert Ron Brightman:

“Silver birch is customarily Betula pendula. It grows large and is an aphid magnet in my area. Betula utilis jacquemontii does not produce the same elegant weeping habit. But the clone commonly sold here displays stark white bark. Mine became infested with what looked to be the same leaf miner that can be quite abundant on native stands of B. papyrifera north of here. Finding the effects of the miners tiresome and this not being a rare tree here, I cut it down. Since native paper birch trees are abundant around Vancouver I would wonder if you might end up with the same problem.”

Here’s another link of interest, from Washington State University. It mentions that “this tree is susceptible to bronze birch borer, a wood boring beetle that will girdle the trunk. Aphids can be problem on the foliage. Excrement from aphid feeding can leave the ground sticky beneath this tree.”

Jacquemontii birch is common as a street tree in Seattle, and as the neighbor of a row of three of these birches, I can say that so far they appear relatively pest-free (I’ve seen a hint or two of sticky aphid honeydew on the leaves ), but they make voluminous leaf and bark litter which blows into my garden. I keep thinking the bark is wastepaper (grocery receipts, etc.). It looks great on the trees, but is a minor nuisance when blown far and wide.

leaf drop in Dogwoods

I have a couple of dogwood trees, both are about 40 years old. In the front yard is a pink dogwood approx 25 ft tall and in the backyard a white one, approx 50 ft tall. Each year in the spring for the past few years the leaves have been browning and falling off the white one. Now the pink one is beginning to develop the same symptoms. Is there anything I can do?

There are several possible causes of leaf drop in Dogwoods. Below, please find referral information for the Master Gardeners and two websites that contain information about pests and diseases of Dogwoods and methods used to control them.

To know for sure what is causing leaf drop in your trees, you may wish to consider bringing a bagged sample of the leaves to the Master Gardeners Diagnostic Clinic here at the Center for Urban Horticulture or another of the many Clinic locations. You can locate a Master Gardener Clinic within King County on this website (Plant Clinic Schedule).

You mentioned that the leaves of your trees turn brown and then drop. These symptoms are commonly found when Dogwoods have been attacked by Anthracnose.
The Washington State University Cooperative Extension’s “Dogwood Anthracnose” page may be of use in helping you determine whether your trees have this disease.

Hopefully, this information will get you started. If you would like more information or have any other questions, please be sure and let us know.

I hope that your trees recover!

managing aphids

I have just taken over management of the small landscaped yard for my condominium and we have two trees (weeping birches I’ve been told) in the front that appear to have been infested with aphids. The trees are about 15 feet tall and are located between the building and the sidewalk to the entrance. They have southern exposure. There’s a few evergreen bushes around the trees, no grass.

I am not familiar with aphid controls, so have done some internet research, including your very useful
site. We want to avoid using pesticides, so from what I’ve read, the best control is insecticidal soap.
Before I try to spray this on the trees I have a few questions I was hoping you could answer.

1. Can you verify that this is aphid damage?
2. It seems to me that the amount of white material on the undersides of the leaves has decreased in the last month. Given that it is getting late in the growing season, is it still worth treating the trees?
3. Does insecticidal soap seem like a good treatment in this situation, and if so do you have any application tips to make sure the undersides of the leaves are treated?
4. Do you have any recommendations for preventative actions to decrease the impact of aphids on these trees in the future?

Birches are commonly afflicted with aphids, and the aphids suck sap and secrete honeydew, which can be a nuisance, and is usually why homeowners contact us. Unfortunately, if your birches are overhanging a sidewalk, it is probably getting sticky from the honeydew. Otherwise, you could probably ignore the problem (except in the most severe infestations).

You can try spraying the aphids off the leaves with a strong jet of water. You can also encourage natural predators. Avoid over-fertilizing, or exposing the trees to lawn fertilizer, for example, as this will lead to succulent new growth which attracts aphids. Make sure the trees are not under any stress, as aphids are more likely to feed on a weakened
tree. You may be able to avoid using the insecticidal soap as a control. If you do use it, you are correct that you need to reach all leaf surfaces, which is labor-intensive. Some of these soaps can cause damage, so it is always a good idea to test any such spray on a small area before coating the whole plant. An article by Colorado State University Extension provides information on insecticidal soaps. Aphids go through many generations in a year, and their eggs can overwinter.

Toxic-Free Future (formerly known as Washington Toxics Coalition) has created a document on managing aphids in the landscape.

Here are additional links on aphid control:

Aphids from University of California at Davis

Managing Aphid Problems without Pesticides from the Northwest Coalition for Alternatives to Pesticides

rust disease and rust-resistant varieties of currant

Our flowering currant has rust disease. It flowers beautifully but looks hideous for most of the summer and fall until its leaves drop. We’re debating whether to remove it, though we love the reddish blooms. Is it affecting other plants in neighboring gardens (for instance, our neighbor’s Heuchera which has rust)? Are there varieties of currant that are rust-resistant?

Your currant (Ribes sanguineum) is probably infected with white pine blister rust (Cronartium ribicola), which also affects some edible currants. As the name of the fungal infection suggests, this is a disease that passes back and forth between its hosts–currants (which aren’t killed by it) and white pine or Pinus strobus (which is seriously harmed by it). Don’t feel guilty about the neighbor’s Heuchera rust, which is caused by a different fungus specific to that plant, Puccinia heucherae. However, if there are white pines within 1,000 feet, the disease could kill them.

The link above mentions that Ribes sanguineum is very susceptible to the disease. Several varieties of edible red currant are rated as virtually immune (‘Viking’ and ‘Red Dutch’), but these are not the type of currant grown for their highly ornamental flowers. I could not find any information about resistant flowering currants, but if there are pines in your neighborhood which have the fungal infection, the rust may continue to be a concern for any future currants you plant.