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

Plant Answer Line Question

Keywords: Trees--Diseases and pests--Washington, Pinus, Master gardeners

Recently we noticed that one of our evergreen trees has a lot of needles that are turning yellowish brown and dropping off. I would say about 25% of the needles are affected, some in the middle of the branches, some at the ends. The needles are about 3 - 1/2 inches long and are in bunches of five - I think it is a pine.

Is this normal for that type of tree? Or is it more likely the tree is stressed for some reason and we need to deal with it?


This will be a lengthy answer and I will assume you live in the Pacific Northwest---the following information will not apply to other areas.

In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic.

Meanwhile, to learn about diseases common to pines in the Pacific Northwest, go to the Pacific Northwest Plant Disease Management Handbook and search using the term pine.
There are several possibilities with good photos. Remedies are included with each disease.

Insect information is more difficult to get, so following are the most likely-sounding pests:

1. Pine (Pinus) - Black pineleaf scale (Nuculaspis californica)

Pest description and crop damage
Mature scales are almost circular, 1/16 inch in diameter, and yellowish brown to black. Young hatch in spring and summer. Scale feeding is restricted to the needles and results in their becoming splotched with yellow patches. Heavy infestations cause premature needle drop and may result in death of the tree. Affected trees often display a thin crown, yellow or reddish coloration, and a shortening of the needles. This insect attacks various species of pine, ponderosa most commonly, as well as Douglas-fir and hemlock.

Biology and life history
This scale overwinters as an immature. The crawlers start to disperse to fresh foliage in spring. There may be one to three generations per year.

Management-cultural control
Trees under stress tend to be particularly susceptible to attack, as are trees growing in dusty conditions. Avoid creating these types of conditions.

Management-chemical control (home)
Dormant season:
Apply with enough water to cover the entire tree thoroughly.
1. horticultural oil. Apply during delayed-dormant period.
Growing season:
insecticidal soap

2. Pine (Pinus) - Eriophyid mites (Trisetacus spp.)

Pest description and crop damage
Eriophyid mites are tiny, wormlike, whitish or tan mites which feed under bud scales or in the needle sheaths, often between the needle bases. Symptoms of eriophyid mite infestations include yellowing, distortion, and stunting of new needles, and development of numerous buds where a bud has been infested (rosetting). Severe infestations may kill needles and cause needle drop, leaving naked branch tips. Rosettes may develop into witches' broom growths. Two-needle pines, particularly lodgepole or shore pine, are affected.

Management-cultural control
Prune out heavily infested growths.

3. Pine (Pinus) - European pine shoot moth (Rhyacionia buoliana)

Pest description and crop damage
Adult moths are reddish-orange with silver markings on the wings. The mature larvae are about 5/8 inch long and reddish-brown with black heads. The larvae of the European pine shoot moth feed on tips of branches, boring first into needles or bud bases, then into the shoots. Infested tips are covered with pitch-covered webbing, often develop a characteristic "shepherd's crook" shape, and may die back. Infested needles are yellowed near the twig tips and eventually turn brown and die. All pines are susceptible, especially two- and three-needle species.

Biology and life history
The insect overwinters as larvae in the mined buds, covered with resin-coated webs. The adult moth lays eggs on new shoots near leaf bases in the late spring. The larvae hatch and bore into the needles, which turn brown by summer. By midsummer, they are mining in the buds and cease feeding by August. There is one generation per year.

Sampling and thresholds: Check for yellowed leaves at shoot tips in midsummer.

Management-cultural control
Prune and destroy infested tips in spring, before adults emerge. Be sure to prune far enough down the branch to remove the insects.

Management-chemical control (home)
1. azadirachtin (neem extract)

Date 2017-05-26
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Plant Answer Line Question

Keywords: Crataegus, Trees--Diseases and pests--Washington

My Hawthorn tree has black spots on the leaves. Can you tell me what disease this might be? In general, what diseases affect Hawthorn trees?


To learn about diseases most common to Hawthorns in the Pacific Northwest, visit the Pacific Northwest Plant Disease Management Handbook and search on the word hawthorn. You will get a list of several diseases that commonly affect hawthorns; click on any of them for a full explanation.

Date 2017-04-22
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Plant Answer Line Question

Keywords: Malus, Trees--Diseases and pests--Washington

My Fuji tree is infected with Cherry Bark Tortrix. Can the branches, leaves, and bark be used as mulch? What should be done with the wood? Can it be stored, and burned in our fireplace?


The leaves and branches can be mulched. The wood can be used, but it is a good idea to strip the logs of the bark and store the wood barkless. Removing the bark will destroy most of the caterpillars in the process. The wood is easier to chop when the bark has been removed, too! If you cannot remove the bark, use a mallet to tap the bark where ever you see galleries. This will most likely squash the caterpillars that are still in the wood.

Date 2017-12-08
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Plant Answer Line Question

Keywords: Thuja plicata, Trees--Diseases and pests--Washington

I have noticed that my old cedar has a very large number of cones on it this year. There are also several areas of foliage that have turned reddish brown. This has all appeared in the past month or less. I live near the arboretum, and notice that there are several cedars in this area that all appear to have these characteristics. But not all of them do, some appear all green with fewer cones. I have not typically noticed this appearance in my cedar before, so I don't know if I am just noticing this for the first time, or whether there is indeed something different going on this year. I am concerned that there may be a disease that is affecting them?


Is your tree a true cedar (Cedrus) or a species of Thuja? The Thuja plicata (Western red cedar) in my garden also had a huge number of cones this year, and just like yours, it has some foliage turning reddish brown. This is probably cedar flagging, as described in this Washington State University Extension page. Flagging--the browning of older leaves and twigs--is a common occurrence on western red-cedar and related trees, such as arborvitae. It usually develops in late summer to early fall. Often, very hot, dry weather, followed by rain, will stimulate the sudden dropping of this older foliage.

If the browning were to be widespread, that might be more of a cause for concern. Additional links:

An image of a cedar suffering from cedar flagging

Cedar Flagging from Private Forest Landowners in British Columbia

Date 2017-01-06
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Plant Answer Line Question

Keywords: Cupressocyparis, Insect pests--Control, Trees--Diseases and pests--Washington

My Leyland Cypress is browning and has Cypress tip moth signs. I'm worried about the brown spots, and wonder if it can survive this attack? How can I control the pests, if it might survive?


From what I can determine, your Leyland cypress (x Cupressocyparis leylandii) trees are probably going to survive this attack unless they are weakened in some other way. x Cupressocyparis leylandii in California survive the Cypress tip moth, though they can be unsightly. Since California is a bit too dry for this tree, the conditions are not identical, but Natural Resources Canada does not indicate that infestations are fatal. Because you said you found evidence of tip moth (Cypress tip moth = Argyresthia cupressella), I will assume that is what the problem is, but a bit of browning, even in conifers, is not unusual right after trees are planted. Be sure that you are not overwatering, as one effect of that is the same as underwatering (i.e., tip die-back or yellowing) because too much water prevents the plant from taking water and oxygen into the roots.

The Organic Gardener's Handbook of Natural Insect and Disease Control (ed. by Ellis and Bradley, 1996, p.183) says about pine tip moth (Rhyacionia frustrana):

Handpicking works if only a few caterpillars are present. Pruning off and destroying infested tips in winter is a very effective control.

I would recommend a prune-and-wait-and-see approach. April is a bit late to prune (and puts root establishment in competition with shoot regrowth), but you may be able to slow the infestation down, so go ahead and do it. Watch the trees this season and then prune again in the winter next year. Be sure to destroy (burn or bag and put in the garbage) the debris so you don't reinfect your tree.

A good gardening resource is the UBC Botanical Garden Forum. Personal testimony/experience is valuable, especially if it's regional. (You might find it useful in the future.) Several people commenting about x Cupressocyparis leylandii note that it is not a very desirable tree; one of its parents, the Cupressus nootkatensis, also called Callitropsis nootkatensis or Chamaecyparis nootkatensis, or, for that matter, plain Nootka cypress) is better. One person recommended planting small trees in the beginning, since they grow very fast. This might save you some money, should you have to replace your trees. The site does not need a password; just click on "Search" in the upper right corner.

Below is some additional information from Oregon State University about cypress tip moth. This site recommends pesticides, but from everything I read, they are not effective without multiple treatments. Since this pest is generally not fatal to the trees, it is probably not worth it to use chemicals which would be dangerous and time-consuming to apply. If you know something about the life cycle of the pest, your observations will yield more information and any manual control attempts are more likely to be effective.

Date 2017-01-11
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Plant Answer Line Question

Keywords: Cedrus, Trees--Diseases and pests--Washington

What is the disease causing needle drop, and even killing in some cases, Cedrus trees in our area? Is there a fungicide recommended to help control the disease, and if so, what timing is recommended?


I can't be absolutely certain what the cause might be, but taking a look at some Northwest integrated pest management resources could provide ideas on the likely culprits.
Oregon State University's IPM site mentions Kabatina and Sirococcus conigenus. Here is what the print companion to the website (2008 Pacific Northwest Plant Diseases Management Handbook) says about Cedar needle blight:
"The fungi Sirococcus conigenus and Kabatina sp. have been associated with blighted needles of Atlas and Deodara cedars in both Oregon and Washington; however, Sirococcus is found most often. More of a problem in years with prolonged wet, cool springs. Infection is on or adjacent to needle bases on new shoots. The disease cycle is completed in 1 year, although spore dispersal from dead parts may continue (...) 10 months. The fungus overwinters in dead shoots. Conidia are dispersed by splashing water in spring and summer. (...) Temperatures of 60 to 70 F are most favorable for disease development.(...) Cultural control: Remove and destroy blight plant material and debris that is found under trees or caught in limbs. Chemical control: No chemicals are specifically registered for this disease on cedar." (The full information is available in the link above.)

Washington State University in Puyallup has a document indexing plant hosts of various pathogens, and for Cedrus they list Sirococcus species as well as Phomopsis.

There are discussions on the topic of Cedrus blights at University of British Columbia Botanical Garden's online forum which mention tip blight sometimes appearing in tandem with borers or mites.

Date 2018-03-14
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August 01 2017 12:36:01