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Search Results for: Plant diseases--Diagnosis | Search the catalog for: Plant diseases--Diagnosis

Plant Answer Line Question

Keywords: Plant diseases--Control, Fungal diseases of plants, Paeonia, Plant diseases--Diagnosis

I planted some peony bulbs last year and they grew nicely until they reached about 10 inches high. One was in the ground, and the other is planted in a medium sized pot outside. The one in the ground is now dead, and the other one is not looking good. It gets dark spots on the leaves, and then the leaves die. Can you help?


Without additional details, it is difficult to say what may be wrong with your peonies. The Penn State Extension has information on different diseases that can affect peony plants. What you describe sounds somewhat like peony leaf blotch or measles, as shown in Iowa State University's Plant Pathology webpage on peony diseases. Here is an excerpt:
"Peony leaf blotch is also known as measles or stem spot. Warm, humid weather provides optimal conditions for infection by the causal fungus, Cladosporium paeoniae.
The leaf spots are glossy and purplish-brown on the upper sides of leaves. On the lower sides, spots are chestnut-brown. Infection is generally more pronounced at the margins of outer leaves. Leaves may become slightly distorted as they continue growing.
Fungal infections on young stems first appear as elongated, reddish-brown streaks. As plant growth continues, infected tissue near the crown may darken and become depressed. Stems on the upper portion of the plant may show individual, raised spots. To manage peony leaf blotch, cut the stems at ground level in the fall or early spring. Rake the area before new shoots appear. Fungicides are available to help control the disease, but must be used in combination with other management practices. Also, providing good air circulation and avoiding wetting the leaves when watering can help reduce disease severity."

There are other possibilities, including peony blight, also known as Botrytis blight. The Royal Horticultural Society discusses this problem:
"Peonies collapse at soil level and the stem bases are covered in grey mould. In a severe attack the leaves are also affected and the plant may be killed or so badly weakened it fails to sprout again next spring. Infections also occur frequently behind the flower buds just before they open.
This is a disease that affects both herbaceous and tree peonies. It is caused by a fungus (Botrytis paeoniae) related to grey mould (Botrytis cinerea), which may also attack peonies in a similar way.
Wilt is encouraged by high humidity which builds up around dense clumps of peonies. Increase the circulation of air by thinning out overcrowded shoots. Also avoid over-feeding, especially with nitrogen-rich fertilisers, which encourages lush, disease-prone growth.
Cut out all infected stems well below soil level, as soon as you notice them. Don't put infected material in the compost bin but burn it or put it in the dustbin, preferably in a sealed bag. If whole plants are badly affected lift and destroy them in their entirety along with the soil surrounding the roots. This total destruction is essential as the fungus can produce black resting bodies (sclerotia), which survive for long periods in the soil ready to re-infect new peonies.
There are no fungicides available to amateur gardeners at present."

I recommend taking plant samples to your local county extension agent for diagnosis.

Date 2018-06-14
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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: Plant diseases--Diagnosis, Hydrangea

Why are the leaves of my oakleaf Hydrangea turning brown around the edges and falling off?


We do not diagnose plant problems, especially without a sample. It might be wise to bring a sample to your local Master Gardener clinic. You can locate a Master Gardener Clinic within Washington State here.

However, based on my personal experience with my own oakleaf Hydrangea (Hydrangea quercifolia), it is a semi-deciduous shrub that will hold on to its leaves through winter, only to replace them with fresh growth in the spring. All my Hydrangea's old leaves have turned reddish-brown and look very ratty. Once new growth resumes in spring, I cut off most of the tattered leaves. (Don't do it too early, in case there is a late frost.)

If you have new growth, do not worry about your shrub, but if you do not have new growth or it is the new growth that is turning brown then you should take a sample leaf into one of the Master Gardener clinics (linked above).

Date 2017-08-15
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Plant Answer Line Question

Keywords: Prunus laurocerasus, Plant diseases--Diagnosis

I am losing leaves on my improved English laurel. They turn bright yellow and fall off. I have heard that some loss is normal, but I have one bush losing at least 15 leaves. They have been in the ground now for 4 weeks.

Second question if I could? When a plant turns yellow from the bottom but the top looks normal and wants to bloom what is the problem. Too much water, etc. It just a small flowering plant and the bottom is getting yellow like it is not happy but the top wants to grow fine.


I will take your second question first: When the oldest leaves turn yellow, but the top of the plant still looks fine, that is usually a symptom of nitrogen deficiency. When nitrogen is deficient in the soil, plants will move nitrogen from the oldest leaves to new leaves, resulting in yellowing, or chlorosis, of the oldest leaves. The Sunset Western Garden Problem Solver recommends using a fertilizer containing nitrogen according to directions on the label for the kind of plant you have. You did not mention what kind of plant it is. The fertilizer will give the plant a quick boost. For longer term health, blood meal or fish meal scratched lightly into soil surface around the plant (follow package directions for amount), topped with a one-inch layer of compost will improve the nitrogen content and overall quality of the soil.

(Adding an inch of compost to planting beds in early spring is a good annual practice for replenishing soil nutrients and keeping plants happy.)

You wondered if too much water could be the problem. Overwatering can produce nitrogen deficiencies in the soil by leaching nitrogen down through the soil and away from plant roots. Different plants have different water requirements. Do you know what kind of plant it is? Without knowing what kind of plant it is, and without seeing it, we can only give possible explanations.

Now back to your first question. There are lots of different patterns of yellowing of leaves and each has a different cause. Is it just the bottom, oldest leaves, or newest leaves, or all leaves, or just the edges of leaves, or just between the veins. I would need to know more before even hazarding a guess. But to get an accurate diagnosis for the problems both of your plants are suffering, we recommend you take samples of each, of good leaves and bad and a little bit of soil from around the root zone of each plant to your local Master Gardener Clinic. You can find a Master Gardener Clinic on the King County Master Gardener website.

Date 2018-04-11
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Plant Answer Line Question

Keywords: Plant diseases--Diagnosis, Juniperus

My Sky Rocket junipers are declining. To me it looks like mite damage accompanied by winter damage. The top of the plant is still healthy looking. There are spider mites present. It does not resemble phomopsis, but could be phytophthora. Please let me know what you think.


I checked Diseases of Trees & Shrubs by Sinclair, Lyon and Johnson and Juniper virginiana does not get phytophthora (or at lease this good authority does not list that disease.) It does list a number of other diseases including blight, canker, phomopsis, among many others.

The HortSense website of WSU Cooperative Extension mentions Juniper webworm, which creates heavy webbing, which could resemble mite webbing.

Of course it could be winter damage, like you guess or nitrogen deficiency if the Ph is high (near a lot of concrete?), or salt damage (from melting ice in past winters?).

You should take a sample in to a Master Gardener clinic. If they do not know the cause, you can ask that they "submit it to the diagnostic center at the Center for Urban Horticulture."

Locate a Master Gardener Clinic within King County at this website.

Date 2017-05-26
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Plant Answer Line Question

Keywords: Seed borne plant diseases, Plant diseases--Diagnosis, Cyclamen

I am a collector of Cyclamens and grow most of my collection in pots. I believe my C. purpurascens are infected with Botrytis, though I have not had this confirmed by any tests. Last year was particularly bad and I had to remove nearly every leaf from both my plants. This summer, as the new leaves emerged, I sprayed the leaves and surface of the grit with a sulfur solution, which seemed to dramatically reduce the infection rate. Now, the infection seems to be back. Can you suggest some methods of control? Do I have to have it confirmed first? I repotted them early this summer, and sterilized the pots and replaced the grit at that time. What else can I do?


What you have done to control Botrytis is what is recommended by the Pacific Northwest Plant Disease Management Handbook. It does indicate the Botrytis can be seed-borne and grow systemically in the plant. Your real solution may be to obtain plants that are certified disease free.

However in researching Botrytis online, I found an article, "Botrytis Blight of Flowering Potted Plants" in Plant Health Progress, from Plant Management Network International. This article was written by a researcher at Cornell University who suggested that Cyclamen are also susceptible to Fusarium wilt and that the symptoms are quite similar. Therefore, I do think it would be wise to take a sample of your diseased plants to a Master Gardener clinic for confirmation. The Master Gardener clinics in Thurston County can be found at their website.

Date 2017-08-15
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Plant Answer Line Question

Keywords: Plant diseases--Diagnosis, Master gardeners, Acer

I have an uncommon maple (Acer ukuruduense) that I planted two years ago, and which one year ago started sending out long stems from the base, so that now it has a vase shape. One month ago the main (original) stem turned black almost to the ground (the bottom two feet or so are still green), and all its leaves turned brown and fell off. Some of the buds still seem viable, but it seems to be dying at the tips. The rest of the plant is so far showing no signs of trouble. I have not been able to figure out what is going on.

1. What is causing this?
2. What, if anything, did I do wrong, and what can I do differently?
3. Might this problem spread to other trees: I have several other small maples in the vicinity.

Other information: The tree is so far just surrounded by bare dirt. This year I watered it frequently with a soaker hose throughout the summer, but last year I was not watering it regularly. It is in full sun, which it is supposed to like.


I am sorry to hear about your diseased maple. Your rare species was mentioned in 2 of our 3 books on maples. However, none of the books describe pests or diseases species by species. The books only give information on "general maple problems." The Gardener's Guide to Growing Maples by James Harris states that maples are "generally trouble-free," but the following can cause problems:
Verticillium wilt, which can kill a tree in a few days, or branch by branch over many years; it is a soil borne fungus that is quite common in Seattle (sorry);
Fusarium, which is another soil borne fungus;
Botrytis, which is a fungus, worst on seedlings, but can also cause die-back on established plants; this fungus favors warm humid conditions;
Die-back, which is not a disease; new growth in fall is not hardened off by winter-time and is killed by cold temperatures.

Take a sample branch into a Master Gardener clinic for a diagnosis (insist they submit it to the CUH diagnosticians if they do not know).

If it is Verticillium you can only slow down the disease by reducing all stress on the tree (keep it well watered and mulched). If your other maples are healthy and established they should be okay, but all are vulnerable to this nasty fungus.

Date 2017-06-09
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Plant Answer Line Question

Keywords: Verticillium, Plant diseases--Diagnosis, Acer

I want to test the roots of our Japanese Maple for Verticillium wilt. Are there places which could test for that?


There is information about Verticillium wilt and how to manage it on the Washington State University Extension's HortSense website.

To have a sample from your Japanese maple diagnosed, you can take samples to a free Master Gardener Clinic, or you can send samples (for a fee) to WSU Puyallup Research and Extension Center:
go to "How to Submit a Sample," scroll down to "Plant Problem Diagnosis," then you can download a form by clicking on "Form C1006."

My personal experience with this disease is that the Japanese maple lived with it for quite a few years before totally succumbing, at which point we had it removed by an arborist.

Date 2017-06-09
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Plant Answer Line Question

Keywords: Powdery mildew diseases, Plant diseases--Diagnosis, Rhododendrons--Diseases and pests, Master gardeners

My rhododendrons have a problem. What appears to be a white powder covers the buds and spreads up the leaves. What is it, and what can I do to stop it?


I cannot be absolutely certain without seeing the plants, but it sounds as if your rhododendrons could have powdery mildew.

Here is an article from the Washington State University Cooperative Extension which describes this disease. One preventive measure you should certainly take is to clean up all the fallen leaves and twigs under your rhododendrons, because the fungus which causes powdery mildew can overwinter there.

You could bring in a sample to a Master Gardener Clinic, and ask if they can diagnose the disease as well (they are at the Center for Urban Horticulture and other locations--see their website.

Date 2017-08-15
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Plant Answer Line Question

Keywords: Passiflora, Plant diseases--Diagnosis, Plant diseases, Master gardeners

I have a passion flower that I brought in for the winter. It has lost all leaves and has sticky little brown spots on it . How do I get rid of the brown sticky things? And how do I get the leaves to grow back. Would putting under a grow light for the winter help.


I read up on Passionflower cultivation and pests in the book Passiflora: Passionflowers of the World by Torsten Ulmer & John M. MacDougal, Timber Press (2004).

Under the section, Overwintering, it says that in winter, passionflowers suffer from lower temperatures, shorter days, and low light, and therefore this season is the most critical period for these plants. Before night temperatures drop below 10 degrees C, the more sensitive container plants, such as Passiflora quadrangularis and P. vitifolia, should be taken indoors. Depending on their resistance to cold, other species will need to be taken to their winter quarters later on; for now, though, these plants should just be cut back and thoroughly scrutinized for pests. Unlike many other decorative plants, passionflowers keep their foliage in winter, with the exception of certain herbaceous species such as P. incarnata, P. lutea, and P. bryonioides. Do you know if your plant is any of those three (so we will know if its loss of leaves is normal and not a sign for alarm)? [This is from p. 49.]

About the brown sticky spots, it is extremely difficult to make a diagnosis or suggest a treatment, sight unseen. If your plant was not supposed to lose its leaves, and the leaf drop is a sign of severe stress, then those spots could be the result of the plant's health being poor (as in low resistance to disease). The spots could be bacteria, viral, fungal or even from some insect (although I read through the list of these and could not tell what it might be).

Your plant would be a great candidate for the Master Gardeners to whom the public can take their plants for advice and diagnosis of problems. I found a Master Gardeners of Ontario, which you can search for your particular region.

Date 2018-04-11
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Plant Answer Line Question

Keywords: Plant diseases--Diagnosis, Clematis

I have a client whose Clematis I just renovated. The client called to say the ends of the cut stems were frothing! What could be causing this?


My best guess (and it is only a guess, since I am basing it solely on your description) is that it could be slime flux. According to the Royal Horticultural Society, "pruned stems may fail to reshoot and ooze a sticky substance--this is known as slime flux." To confirm this theory, ask the client if the frothy ooze was pinkish orange in hue, and if it had an unpleasant odor. Here is more about this problem from the Daily Telegraph's garden advice column by Helen Yemm excerpted below:
"This is not so much a disease as a condition that affects some trees and shrubs in spring. Bacteria enter the plant through cracks in the stem - which may well be caused by a combination of adverse weather conditions - and then attack the sap as the plant springs into action early in the year.
Slime flux is often fatal but it depends where the damage is. Everything above the oozing wound will certainly die and should be cut down. However, the plant may well shoot out from below and recover.
Slime flux will not spread to other plants as diseases do, nor will it contaminate the soil like clematis wilt. However, its occurrence would indicate that, for some reason, the general growing conditions in that part of the garden have become unsuitable. If you do lose your clematis, then perhaps it would be a better idea to plant a new one in a less exposed spot."

Date 2017-08-24
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Garden Tip

Keywords: Insect pests--Identification, Plant diseases--Diagnosis, Plant diseases

National Gardening Association's Pest Control Library is a pictorial guide to diagnosing pests and diseases. Every article has a color picture to help confirm if the pest in question looks like the bug eating your plant. Major plant diseases are also included and organized by the part of the plant it infects: leaf, fruit, roots or all parts.

Date: 2007-07-13
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May 31 2018 13:14:08