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Search Results for: Trees--Diseases and pests | Search the catalog for: Trees--Diseases and pests

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How To Identify and Control Noninfectious Diseases of Trees

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Plant Answer Line Question

Keywords: Insect pests--Control, Trees--Diseases and pests, Pesticides

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., Washington State University's Forest Health Notes (page 9) states that the focus has shifted from using pesticides to taking preventive measures:
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.

Date 2018-04-21
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Plant Answer Line Question

Keywords: Abies, Plant diseases--Diagnosis, Trees--Diseases and pests

Can I attempt to diagnose a diseased tree online? We're getting more brown spots on our grand fir and I would like to try to figure out what is wrong.


You can attempt it, but you will not know for certain based solely on a comparison of symptoms. You can certainly get an idea of what the potential problems could be. Try the Pacific Northwest Plant Disease Management Handbook online---it has excellent photos. Search for fir.

There are several possibilities with brown spots as symptoms, especially:
*needle casts (there are 3 kinds)
*web blight
*current season needle necrosis
*shoot blight
*Grovesillea canker
*interior needle blight

The best way to diagnose a problem is to bring photos of the affected tree along with samples (if you can reach them) to your local county extension agent or Master Gardener diagnostic clinic.

Date 2018-06-14
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Plant Answer Line Question

Keywords: Cornus kousa, Cornus florida, Powdery mildew diseases, Trees--Diseases and pests

Where can I find information about dogwood hybrids, especially crosses between Cornus kousa and C. florida? Won't these trees be more resistant to the mildew affecting many dogwoods?


In addition to powdery mildew, many dogwoods can suffer with anthracnose. In his book Dirr's Hardy Trees and Shrubs (Timber Press, 1997), Michael Dirr mentions Rutgers Hybrids (which are a cross of the kousa and florida species of Cornus). These trees were developed at Rutgers University by Elwin Orton, and are resistant to dogwood anthracnose. This article from North Carolina State University Extension discusses powdery mildew resistance. Scroll to the second table at the end which charts cultivars and their resistance or susceptibility to powdery mildew.

Oregon State University provides information about each of the six hybrids of C. florida x C. kousa. Two of the trees on this list are resistant to powdery mildew.

Clemson University Extension offers further information about the insects and diseases affecting dogwoods.

Date 2018-06-14
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Plant Answer Line Question

Keywords: Cornaceae (Dogwood family), Trees--Diseases and pests

I live in Kitsap and my 50-year old maple is dying -- what should I do?

Also, my Dogwood trees seem to be infected with anthracnose. Can you give me some information about this disease?


To get some information about your maple, you can consult with a Master Gardener at a WSU Kitsap County Extension Diagnostic Clinic.

Regarding dogwood anthracnose (Discula destructiva), it is a shame that so many of these beautiful trees are infected. You may be somewhat reassured to know that although the disease often causes tree death in the northeastern U.S., here in the Pacific Northwest, many trees survive. Douglas Justice, Curator of Collections at University of British Columbia Botanical Garden, discusses this on the UBC discussion forum.
"Weather is probably the deciding factor in infection. A cool, wet period seems to be most conducive to infection, and such factors probably have to coincide with a specific time of tissue susceptibility. In other words, the conditions have to be "just right" for the disease to take off and become established. However, it is well documented that stress predisposes plants to disease susceptibility. Stressors for Cornus nuttallii (Pacific dogwood) would include compacted soil, poor drainage, full exposure with overly dry soil (C. nuttallii is adapted to a summer drought regime, but let's be reasonable!) and wet soil in summer (e.g., irrigated soil -- see previous comment). Nearly all the local anthracnose-affected dogwoods recovered, including the wild natives and the even some of the more severely affected C. florida (eastern dogwood). Anthracnose has visited us subsequently, but mostly only on C. florida and urban C. nuttallii. This suggests that the there isn't much anyone can do to prevent the disease from occurring and that as along as trees aren't overly stressed, they will eventually recover. "

A U.S. Forest Service article entitled How to Identify and Control Dogwood Anthracnose includes images which may help you to determine if your tree has anthracnose.

Master Garden Products.com provides a short article about dogwood anthracnose that contains a What to Do list.

University of Maryland College Home and Garden Information Center's Integrated Pest Management Series HP #12 offers information about dogwood diseases and pests, including anthracnose.

Oregon State University Extension's Online Guide to Plant Disease Control describes cultural controls for anthracnose. There is also an extensive list of chemical controls, which you may choose to ignore after reading Douglas Justice's comments from the UBC discussion forum mentioned earlier:
"The application of fungicides is probably a waste of money and also likely counter-productive, particularly with a systemic such a benomyl, which will kill most of the good fungi, but probably not the target pathogen. Common fungal pathogens frequently develop resistance to this fungicide."

Date 2018-06-27
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Plant Answer Line Question

Keywords: Pruning shrubs, Cotinus coggygria, Cornaceae (Dogwood family), Trees--Diseases and pests

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:
The U.S. Forest Service article entitled How to Identify and Control Dogwood Anthracnose, may be of use. Although it is somewhat technical in its language, there are excellent pictures and a section about methods of control.
Master Garden Products.com provides a short article about Dogwood Anthracnose that contains a What to Do list.
Oregon State University Extension's Online Guide to Plant Disease Control 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 among those plants which respond well to this pruning technique.

Date 2018-03-01
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Plant Answer Line Question

Keywords: Cornus florida, Trees--Diseases and pests, Master gardeners

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?


Thank you for your question about Dogwoods. 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!

Date 2017-08-15
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Plant Answer Line Question

Keywords: Tsuga heterophylla, Trees--Diseases and pests

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


The USDA Forest Service has an entire web site devoted to this pest problem, and 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 (Western hemlock). You can obtain referrals from Plant Amnesty or you can select an arborist from the Pacific Northwest Chapter of the International Society of Arboriculture.

Date 2018-04-21
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Plant Answer Line Question

Keywords: Abies, Trees--Diseases and pests

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 Connecticut Agricultural Experiment Station has published a guide entitled "Recognizing and Managing Phytophthora Root Rot and Other Conifer Diseases" which may be of use to you. (Caution: this is a large file!)

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.

Date 2018-05-23
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Plant Answer Line Question

Keywords: Aphids, Betula, Trees--Diseases and pests

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

Date 2017-08-04
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Plant Answer Line Question

Keywords: Cupressus, Moths, Trees--Diseases and pests

I haven't been able to find much about control of cypress tip moth on true cypress (Cupressus). I'm looking for a non-toxic control instead of the WSU recommendation of Orthene. Would Neem possibly work? Spinosad? Both are registered for leaf miners (fly larvae), but this is a moth larvae. Bt won't work because the larvae are inside of the foliage. What's the best timing for a non-toxic? WSU recommends controlling the adults in July-August.


University of British Columbia Botanical Garden's forum has this to say:

"In the west, cypress tip moth sometimes infests cypress (Cupressus and Cupressocyparis) and false cypress (Chamaecyparis); those are also sometimes called cedars. In the east, cedar often refers to Juniperus (red cedar), Thuja or Chamaecyparis (white cedar); all are subject to bagworm infestations and various tip-miners. In the west, timely shearing is the most effective way to control cypress tip moth, and this may also be a tactic in other parts of North America.

"In many cases, infestations occur because there are few natural enemies about to reduce pest levels. Sometimes, pests are attracted to plants that are already weakened by stress. Healthy plants and diverse plantings, together with a reduction in pesticide use, will over time, increase beneficial organisms which will in turn reduce pest levels. Spraying to reduce pests generally affects beneficials to a greater degree than the actual target pest. This is because pest species often have a greater capacity to rebound -- they often reproduce faster, have a greater tolerance for pesticide residues and have a greater capacity to become resistant to pesticides."

Oregon State University's IPM site only mentions chemical controls.

From an online forum, 'Horticulture Guy:'

Q. I have a row of 16 - three year old "Emerald Green" arborvitaes. I suspect they have arborvitae leafminer (cypress tip moth). I have noticed the moths before, but now there are more and I just recently noticed brownish-yellow tips on a couple of the trees. All of them have lots of needles falling from the interior. My problem is that I have received conflicting reports about the proper time to spray for them, and is there anything I can do in the meantime to lesson the damage? Thank you! Linda Brieger - Tacoma, WA

A. The way to gain control over any pest population is to know its life cycle. Spraying is geared toward eliminating the adult form of the insect, which is a moth as the second of the two common names indicates. The most likely reason you may see conflicting reports on when to spray the moths is because of varying times the moth may emerge in different regions where they are present. They are generally active in our area from April to June with a peak of activity in May. The moths lay their eggs during this period and the eggs hatch and then burrow into the needles of the host plant. According to the WSU extension the adult moths are silver-tan and approximately 1/4" in length. External sprays won't have an effect on the larvae once they burrow so you need to spray weekly during this period to catch the larvae as they hatch. Systemic insecticides are able to kill the larvae once they are in the host. You can limit systemic insecticide spraying to one application near the beginning of the activity since they generally remain effective for some time (see labels for instructions). As far as "in the meantime" a sprayless solution is to prune out and destroy infected parts of the host now so that there are less moths in the spring. You can also keep an eye out in the spring for the white cocoons that form after the larvae exit the host to become adult moths. You can remove these as well.

University of California Integrated Pest Management suggests that proper cultural care and removal of susceptible plants is the answer. Excerpt:

Provide proper cultural care to keep plants vigorous. Prune out and dispose of foliage infested with immature leafminers to restore the plant's aesthetic appearance and provide some control. Consider replacing plants especially susceptible to the cypress tip miner. High populations and damage can be reduced on established plantings by applying a broad-spectrum, persistent insecticide such as acephate on susceptible varieties when adult moths are active. Beginning in early spring, examine foliage tips for the cocoons. When these appear, vigorously shake foliage and watch to see if silvery tan, tiny moths fly up then settle back on the foliage. One application to foliage can be made when a large number of tip moths appear, between March and May in California. This reduces browning next season.

You could try using the Neem oil (instead of the more toxic alternatives) although I did not find any information specifically suggesting this as a control for cypress tip moth. The WSU book, Pacific Northwest Landscape IPM Manual (2002) suggests natural parasites which attack this species of insect, but they do not specify the identity of these predators. They state that there are no "biorational pesticide management options" for this pest.

Date 2018-06-07
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Plant Answer Line Question

Keywords: Flowering cherries, Trees--Diseases and pests, Prunus

We have a mature ornamental cherry or plum tree that suffered from brown rot last year. We removed all affected branches and leaves. We were told that we might need to do something else this winter or spring--spray the tree with something, possibly. Can you advise us on how to keep our tree healthy?


I consulted The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996), and this resource recommends doing what you already did, by removing and destroying affected parts of the tree. At the beginning of the growing season (early spring) you can spray sulfur to control this fungal disease on blossoms. If you were growing fruit, you would spray again later in the season to protect the fruit, but since this is an ornamental tree, it isn't necessary. Copper sprays are also used to control the disease. Washington State University Extension recommends preventive measures, such as avoiding wounding trees (damaging bark with string trimmers/weed-whackers/lawnmowers, or making bad pruning cuts). Avoid wetting the blossoms and leaves, and keep the tree pruned for good air circulation in the canopy. Avoid excessive nitrogen fertilizer. While the tree is in bloom, check it frequently for symptoms, and destroy any diseased parts as soon as you notice them.

I found sources for less toxic (but still not hazard-free) versions of these fungicides from Peaceful Valley Farm & Garden Supply, but they may be available at your local garden center as well. Some of these require a pesticide handler's license.

Lime Sulfur Fungicide

Copper Sulfate

Date 2018-06-27
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Plant Answer Line Question

Keywords: Magnolia grandiflora, Trees--Diseases and pests

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.

Date 2017-12-08
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Plant Answer Line Question

Keywords: Betula, Trees--Diseases and 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.

Date 2017-08-15
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Plant Answer Line Question

Keywords: Trees--Diseases and pests, Ribes

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.

You may find this blog post by a Seattle gardener of interest.

Date 2017-05-25
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Garden Tip

Keywords: Biological control, Insect pests--Control, Pesticides and wildlife, Trees--Diseases and pests

Gypsy moth is often in the news and with it comes the promise of aerial spraying of Btk by the department of agriculture. While the idea of the government spraying pesticides over an entire neighborhood may be frightening, a gypsy moth out-break would be devastating to the trees of the Emerald City or any city. Gypsy moths defoliate over 500 species of trees, both deciduous and evergreens.

Bacillus thuringiensis var. kurstakiis a bacterium that affects only caterpillars. It is considered an acceptable pesticide by organic gardeners, provided it used only when really needed. The major caterpillar pests in our area include:

  • the larvae stage of the gypsy moth;
  • cutworms that feed in winter and spring on primroses, chives and other perennials;
  • tent caterpillar often seen later in the spring on apple trees;
  • keep in mind that sawfly larvae which can strip a flowering red currant bare in a few weeks are not caterpillars, and Btk will not control them.

Btk will kill caterpillars of butterflies, which is why it must be used with caution only when pest populations are high or the potential damage is intolerable. Btk is typically sold as "caterpillar killer" where other pesticides are sold.

Date: 2007-04-20
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Garden Tip

Keywords: Reference books, Woody plants--Diseases and pests, Integrated pest management, Trees--Diseases and pests

A reference book is available to help gardeners solve pest problems. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide (University of California, $42.00) diagnoses common diseases, insects and environmental stresses with color photos and suggests appropriate solutions. This book also has a chapter on how to get your plants off to a healthy start with proper planting techniques.

The Integrated Pest Management approach tell us the most important fact to remember about plant problems is that poor growing conditions like soggy roots or bone-dry roots inevitably leads to pests and diseases. Select the right plant for the garden conditions to avoid problems later.

Date: 2007-04-03
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Garden Tip

Keywords: Tree identification, Trees--Diseases and pests, Trees--Care and maintenance, Trees

Silvics of North America Online by United States Department of Agriculture Forest Service, 1990.

Property owners with woodlots and tree lovers alike will find the Silvics of North America an informative and authoritative reference source on trees. Two hundred, mostly North American native trees are described including native habitat, associated trees and shrubs, propagation details, growth rate, and information on the major pests that may damage the tree. Many entries have information on the root development, which can be helpful in learning if a chosen tree will tolerate construction, or be appropriate for planting over water utilities.

Date: 2007-07-12
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