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Search Results for ' Fungal diseases of plants'

PAL Questions: 12 - Garden Tools: 2

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

PAL Question:

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?

View Answer:

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.

Season All Season
Date 2008-01-10
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Keywords: Euonymus, Fungal diseases of plants

PAL Question:

I am considering using Euonymus 'Green Spire' for a hedge. My experience with Euonymus japonicus is that every year it seems to get mildew and drop leaves. Is this likely to happen with the 'Green Spire' as well? Do you have any suggestions about how to treat the mildew or avoid it?

View Answer:

'Green Spire' is a variety of Euonymus japonicus. This plant can suffer from a fungus, Oidium euonymus japonici, which occurs only on Euonymus japonicus, and is found wherever the host grows. Clemson University Extension says that fallen leaves and heavily affected branches should be disposed of. Plant in a sunny site which is not overcrowded, and do not water from above.

According to University of California, Davis's Integrated Pest Management site, variegated forms of Euonymus are less susceptible to mildew. Preventive measures are the first step, but if your plants already have mildew, this resource lists less toxic fungicides, such as Neem oil, jojoba oil, baking soda spray, potassium bicarbonate, and biological fungicides: "With the exception of the oils, these materials are primarily preventive, although potassium bicarbonate has some eradicant activity. Oils work best as eradicants but also have some protectant activity."

Season All Season
Date 2006-10-05
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Keywords: Fungal diseases of plants, Mushrooms, House plants

PAL Question:

I have a potted plant with a fungus growing in the soil. It is bright neon yellow and grows like a mushroom, but with no cap on top. The plant is in the basement near a window. The soil is damp and I've avoided watering for awhile to let it dry out. What do you think the growth is, how to get rid of it, and will it be harmful to my plant? I keep plucking them, but they grow back.

View Answer:

I have had questions about the yellow houseplant mushroom before, and I am guessing you are seeing the same thing. It is called Leucoprinus birnbaumii. Bio.net's pages have additional information about it. Excerpt:

"Your shrooms are most likely Leucocoprinus birnbaumii. This harmless (to your plants) fungus is a common contaminant of potting mixes. Pick off the mushrooms before they can shed spores, and try watering your plants deeply but less often so that the soil does not stay soggy. Also, these guys can cause real internal upset if ingested, so make sure the kids and pets don't get to them."

Michael Kuo's website, MushroomExpert.com has information about Leucoprinus as well. Excerpt:

"This little yellow mushroom and its close relatives are the subject of many frantic e-mails to MushroomExpert.Com, since it has a tendency to pop up unexpectedly in people's flower pots--even indoors! The brightness of its yellowness exhibits some rebelliousness, but it often creates a striking contrast to the green houseplants that surround it.

"Leucocoprinus birnbaumii won't hurt you, unless you eat it. It won't hurt your plant. It won't hurt your pets or your children, unless they eat it. There is no getting rid of it, short of replacing all the soil in your planter (and even then it might reappear). Since it makes such a beautiful addition to your household flora, I recommend learning to love it--and teaching your children to love it, too.

"You might also impart the idea that mushrooms are very, very cool--but shouldn't be eaten. Perhaps your child would like to become an awesome and famous mycologist some day. I would love to encourage your child's interest in mushrooms by putting his or her drawing of Leucocoprinus birnbaumii on this Web page (at least temporarily).

"Leucocoprinus birnbaumii is probably poisonous; do not eat it. Handling it, however, won't hurt you."

Season All Season
Date 2007-06-20
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Keywords: Fungal diseases of plants, Insect pests, Lonicera

PAL Question:

I noticed my honeysuckle, which is intertwined to look like a topiary bush with the greens and flower all bunched up at the top, to have yellowing of the leaves and drop off. Why are the leaves yellowing? It smells lovely and is green on the outside, but if you look under the canopy you can see many yellow leaves. Is it a disease? Should I use a fungicide?

View Answer:

There are a few possibilities. It might be a kind of leaf blight, as described by Iowa State University Extension.

Leaf blight is a fungal problem, but the control methods described above are not nontoxic, so you may want to look for a safer fungicide (example here), and also try to prevent the ideal conditions for fungus. Avoid wetting the leaves of the plant, and make sure there is good air circulation around the plant (by siting it properly, and by pruning to keep the plant's shape open).

Yellowed leaves could also be caused by scale, which is an insect. Do you see small bumps on the leaves and stems? If so, here are recommendations from The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale, 1996):

"Minor infestations can be controlled by scraping the insects off the plant with your fingernail, and by pruning out the most infested parts of the plant. You can also use a soft brush and soapy water to scrub scales off the stems, or you can apply dormant oil to the trunk and stems of the plant just before growth begins next spring, and use superior oil during the growing season."

Because I'm not certain which type of problem your honeysuckle may have, you should bring a sample to a Master Gardener Clinic.

Season All Season
Date 2008-02-07
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Keywords: Fungal diseases of plants, Huckleberries, Gaultheria shallon

PAL Question:

We have 5 acres that are covered in 50-year-old fir and cedar forest, with lots of salal and evergreen huckleberry. The huckleberries have what looks like mummy berries that I have seen in photographs of blueberries before. They have a dry grey peeling that feels like old garlic skin with a very hard brown inside. There doesn't appear to be any problem with the foliage. These bushes are naturally growing, and are all over through the property. Mulching and cultivation would be nearly impossible on this scale, and I'd really prefer not to spray if possible. Can you suggest a safe method of control that would be possible on this large scale? Or is this something that nature will take care of on its own? Or do we even need to worry about it since we don't harvest the berries? I can live with a few shriveled berries. I just don't want it to spread wildly or kill off half of our underbrush.

View Answer:

If mummy berry is what you are seeing (and it does sound like it), it is caused by a fungus which overwinters in the fallen berries, so anything you can do to collect them might help. The following, from Ohio State University Extension, describes the life cycle of this fungal problem.

The Organic Gardener's Handbook of Natural Insect and Disease Control by Barbara Ellis (Rodale, 1996) recommends removing the berries and in spring, cultivating around the bushes to bury any fallen mummies, or adding mulch to cover fungal spores.

Beyond the good hygiene of removing the fallen fruit, there may be a chance that wettable sulfur spray might help, as described in this information from McGill University. Excerpt:

"Clean cultivation can reduce the incidence of mummy berry disease. This practice destroys the fallen mummified fruit, which harbors the inoculum for the next season's infection. Wettable sulfur sprays have also been effective in reducing mummy berry infection. In New Jersey, researchers used three sprays roughly one week apart with the first spray timed for leaf emergence in the spring."

However, I found Ohio State University contradicting this information, indicating that organic fungicides such as sulfur and copper were ineffective against mummy berry.

Here is additional information from National Sustainable Agriculture Information Service. Excerpt:

This fungus overwinters in mummified berries that have fallen to the ground. Sod or moss directly under the plant will contribute to spore production. To control this fungus, remove infested fruit ("mummies") from the plant, rake and burn mummified berries, or cover the fallen berries with at least two inches of mulch. Cultivation during moist spring weather will destroy the spore-forming bodies. Strategies that lead to early pollination of newly open flowers may be useful in managing mummy berry disease in the field, since studies show that newly opened flowers are the most susceptible to infection and that fruit disease incidence is reduced if pollination occurs at least one day before infection.(Ngugi et al., 2002)

The fungus survives the winter on dead twigs and in organic matter in the soil. The disease is more severe when excessive nitrogen has been used, where air circulation is poor, or when frost has injured blossoms. Varieties possessing tight fruit clusters are particularly susceptible to this disease. Remove dead berries, debris, and mulch from infected plants during the winter and compost or destroy it. Replace with new mulch, and do not place mulch against the trunk of the plant.

I'm afraid there is not an easy solution for such a large expanse of huckleberries. Then again, if you are not concerned about harvesting the fruit, then you can probably just let it be. Since the fungus seems to be a problem primarily for plants in the blueberry family, I do not imagine it will harm other plants on your property.

Season All Season
Date 2007-10-11
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Keywords: Prunus laurocerasus, Fungal diseases of plants, Bacterial diseases of plants

PAL Question:

I have some laurel bushes that are developing black or dark brown leaves. It starts at the top and then works down. Trimming them off seems to help but then another bush develops the problem. I want to take care of this before it gets out of control. A neighbor had an entire laurel die--it was probably 15 feet tall.

View Answer:

While I cannot diagnose a plant problem via e-mail, it might be a bacterial or fungal problem, or an environmental disorder. I am assuming your laurels are English laurels (Prunus laurocerasus), not Mountain laurels (Kalmia). According to the Oregon State University Extension's Plant Disease database, English laurel can suffer from leaf spots and shothole. Excerpt:

Cause: Shothole symptoms are commonly observed on Prunus sp. and can be caused by a variety of factors. The bacterium Pseudomonas syringae pv. syringae and several fungi including Cercospora sp., Blumeriella sp., and Wilsonomyces carpophilum (Coryneum blight) can cause leaf spots and shothole on cherry laurel (English laurel, Otto Luyken, or 'Zabeliana'). Copper spray injury and boron toxicity can also cause leaf spotting and shothole. When symptoms are advanced, it is not possible to identify the cause specifically.

Cherry laurels (English laurel, Otto Luyken, or 'Zabeliana'), P. laurocerasus and sometimes other Prunus sp. including cherry and plum, commonly show shothole symptoms resulting from cultural or environmental stress. Research has failed to identify what specific stress is responsible. Both container- and field-grown laurel can develop symptoms.

Symptoms: Necrotic leaf spots with circular to irregular margins. Bacterial spots are brown surrounded by a reddish border with a yellow halo. Abscission layers develop around necrotic leaf spots causing the injured tissue to drop away, leaving holes and tattered areas in the leaf (as if someone fired a shotgun at the leaf-thus the name shothole). After tissues drop, most often it is difficult to determine specifically what caused the initial injury. Observations of early symptom development, signs, and symptoms on other areas of the plant may help make an accurate diagnosis. Note the holes in the leaves.

Cultural control: No management practices have been shown to help reduce physiological shothole. For disease-induced shothole, try the following cultural practices.

  • Avoid overhead irrigation.
  • Remove and destroy fallen leaves.
  • Do not plant near other flowering or fruiting Prunus sp.

If the problem is shothole, this is usually an environmental disorder, and infected parts of the plant should be removed and destroyed.

Here is more information from U.C. Davis Integrated Pest Management on bacterial blight, which in laurels usually affects only the leaves.

If you want to be sure of what the problem is, I suggest bringing samples of the affected leaves to one of the Master Gardener Clinics in our area.

Season All Season
Date 2007-10-11
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Keywords: Rosa, Plant diseases--Control, Fungal diseases of plants

PAL Question:

What can I do about black spot on my roses? I heard that burying banana peels in the soil might help.

View Answer:

According to The Organic Gardener's Handbook of Natural Insect and Disease Control (edited by Barbara Ellis; Rodale Press, 1996), there are several steps to dealing with black spot on your roses. First, avoid wetting the leaves, and do not handle the plants when foliage is wet. Prune the plants to make sure there is good air circulation. Make sure the roses are in sun, and are not shaded by large shrubs or trees. Avoid using high-nitrogen fertilizers, and only fertilize based on a soil test's indications. If you expect an appearance of black spot (based on past experience), spray plants weekly with sulfur or fungicidal soap. Once you see symptoms, it is hard to control black spot. Remove and dispose of any affected parts of the plant (don't compost). Make a solution of 1 teaspoon baking soda in a quart of water, and spray the infected plants well.

University of California, Davis's Integrated Pest Management website says the following about black spot (Diplocarpon rosae):

"The fungus requires free water to reproduce and grow, so leaves should not be allowed to remain wet for more than 7 hours. (When hosing off aphids, do it in the morning so leaves have a chance to dry by midday.) Provide good air circulation around bushes. Remove fallen leaves and other infested material and prune out infected stems during the dormant season. (...) Miniature roses are more susceptible than other types, although a few varieties are reliably resistant to all strains of black spot.(...) A combination of sodium bicarbonate or potassium bicarbonate plus horticultural oil (as discussed above under "Powdery mildew") or neem oil has also been shown to be effective in reducing black spot."

Brooklyn Botanic Garden has information on natural disease control, including the following:
"Baking soda (sodium bicarbonate) is non-toxic, readily available, and very inexpensive. It can be effective against powdery mildew and somewhat useful against black spot. If you repeatedly spray leaves with bicarbonate, though, it will eventually reach the soil below, where it can accumulate and lead to slower plant growth. Bicarbonate can form insoluble particles with calcium and magnesium ions when it concentrates in the soil, making these important nutrients unavailable to plants. High levels can also prevent plants from absorbing iron and can lead to chlorosis.
Bicarbonate is most likely to build to damaging levels in drought-stressed areas where there is little rain to flush it away. It is also likely to build up when applied in a small area, and when used in conjunction with drip-type irrigation. Garden situations are so complex that it is hard to predict the point at which you will see adverse effects. Stop applying bicarbonate sprays, however, at the first sign of plant damage or lower quality blooms."

Brooklyn Botanic Garden also mentions a beneficial bacterium which may provide some help:
"Preliminary research shows that the beneficial bacterium Bacillus laterosporus (sold as Rose Flora) is as effective at protecting black spot-susceptible rose cultivars as some chemical fungicides. It probably protects against black spot through competition, but this agent is still relatively new and experiments detailing its mode of action have not been completed. As a ground spray, it can help control new sources of black spot infection. As a foliar spray, it seems to be more effective when mixed with the antitranspirant sold commercially as Wilt-Pruf. The powdered formulation can cause eye irritation, so use eye protection when mixing solutions and applying."

About the practice of using banana peels to control black spot on roses, I found the following item on Gardening Folklore from Ohio State University Extension, which suggests the peels might be a good fertilizer, but does not say they will control the fungal problem.
Excerpt:
"Placing several banana peels in the planting hole was popular among rose growers in the 18th century, but they had no idea why the peels seemed to yield healthier roses. Today, we know that banana peels contained many useful nutrients, including calcium, magnesium, sulfur, phosphates and sodium. The peels rot quickly which means these nutrients are readily available to the plant."

Some sources recommend using compost tea or milk sprays on black spot-affected leaves, but Washington State University Horticulture Professor Linda Chalker-Scott dismisses these methods as ineffective. She also states in an article in Master Gardener magazine (Spring 2009) that baking soda sprays may only be of limited efficacy in combatting black spot. Studies have shown that it works better when combined with horticultural oil.

To sum up, I would pay attention to the cultural practices (not wetting the leaves, etc.). You can try a baking soda spray (always test on a small area of the plant first), but it may not have lasting power as a treatment. Prof. Chalker-Scott mentions that coarse organic mulch (such as wood chips) reduces incidence of black spot, so you may want to adopt this mulching practice.

Season All Season
Date 2008-05-03
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Keywords: Rosa, Insect pests--Identification, Fungal diseases of plants

PAL Question:

I have several roses that bloom just fine but one particular rose bush produces buds that never open. Why is this happening?

View Answer:

It is possible that your rose has a problem with insects like thrips, which can cause buds not to open. If you see tunneling in the buds (holes in the petals), it could be caused by beetles. There is also a possibility that a disease is causing the problem. Fungal infections like botrytis blight can result in buds which do not open, but you would probably notice signs of the fungus during warmer temperatures, such as gray-brown fuzzy growth, and blotched petals or drooping buds. The Northwest Center for Alternatives to Pesticides published information in their Journal of Pesticide Reform, Summer 2004 issue, describing various rose problems, and organic solutions.

Here is a description of botrytis blight from University of California, Davis Integrated Pest Management. This is a brief excerpt:
"Botrytis blight, caused by the fungus Botrytis cinerea, is favored by high humidity. Affected plants have spotted flower petals and buds that fail to open, often with woolly gray fungal spores on decaying tissue. Twigs die back and large, diffuse, target-like splotches form on canes. Reduce humidity around plants by modifying irrigation, pruning, and reducing ground cover. Remove and dispose of fallen leaves and petals. Prune out infested canes, buds, and flowers. Botrytis blight is usually a problem only during spring and fall in most of California and during summer along coastal areas when the climate is cool and foggy."

The Olympia Rose Society also has information on these potential causes of failed buds. Below is their description of thrips:
"Buds do not open, or flowers are deformed. Petals have brownish yellow streaks and small dark spots or bumps. White and pastel roses are particularly susceptible. Thrips (are) tiny orange insects with elongated bodies. Thrips feed at the bases of rosebuds and on the petals of open flowers. They seem to be attracted to light-colored blossoms."

The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) suggests encouraging natural predators of thrips and, if the infestation is severe, spraying weekly with a safer insectidical soap or pyrethrin-based product. This same resource suggests that if your roses have botrytis blight, you will see the buds turn brown and decay instead of opening, and you should pick off and dispose of any diseased buds. They recommend spraying with sulfur once a week during the growing season.

A few things that are always a good idea when growing rose:

  • make sure there is good air circulation around your plants
  • don't water from above the plants (keep the leaves dry)
  • always clean up around the plants--don't let leaf debris or any diseased buds lie on the ground under the rose bushes

This site has many pictures of rose pests and diseases for you to compare with what you are seeing on your plant. Since I cannot diagnose the problem without seeing the plant, I recommend that you take samples of the affected buds to a Master Gardener Clinic.

Season All Season
Date 2008-11-01
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Keywords: Photinia, Fungal diseases of plants

PAL Question:

I have a 75-foot long Photinia x fraseri hedge that is losing leaves. The leaves have dark spots on them. I wonder if it is a mold or fungus. I have not removed trimmings in previous years and air circulation has not been optimum. Some plants have lost almost all their leaves but there is new growth there too. The hedge is about 4 feet tall and is about 20 years old. I was thinking it could use some sort of fertilizer and mulch after I clear out all the old prunings. Any suggestions?

View Answer:

There are a few possible reasons your hedge is dropping leaves. In my own experience with Photinia, they were constantly dropping leaves throughout the year. Some of the leaves had dark spots, but some were just older foliage, reflecting this plant's tendency to shed older leaves. According to Washington State University's Landscape Plant Problems (2000), spots on Photinia leaves can be caused by a fungus called Entomosporium mespili, but they can also occur in fall and winter with no disease present. The fungal spots tend to have purple black edges and ash grey centers. Virginia Cooperative Extension has descriptions and images of this fungal disease.

There is another leaf spot of unknown origin, simply called 'physiological leaf spot,' described by Washington State University Extension as follows:
"Physiological leaf spot occurs on Photinia in western Washington. The symptoms resemble those of early fungal leaf spot infections. Small red to purple spots appear on the leaves, but do not develop the dark centers characteristic of fungal leaf spot infections. This problem is more common than fungal leaf spot. It causes little damage to plants, although some leaf drop may occur. While the cause of this problem is unknown, leaf spotting appears to be more severe on plants in low-lying or shady areas. Cold temperatures appear to be involved."

If you want to know for certain what the spots are, you should bring samples to your local county extension agent so that they can identify the cause.

Improving air circulation and removing and disposing of all fallen leaves are always good garden hygiene practices. Avoid getting the leaves wet when you are watering the garden, and avoid summer pruning. The American Horticultural Society book Pruning & Training (DK Publishing, 1996) recommends pruning in spring, though hedges will need to be clipped two or three times a year.

I don't recommend adding fertilizer, as it could cause your hedge to grow more quickly than you want to prune it. Mulching lightly with compost would probably be beneficial. In general, Photinia is a tough and vigorous plant, and the leaf spots are unlikely to cause its demise.

Season All Season
Date 2008-11-13
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Keywords: Fungal diseases of plants, Fungi, Prunus

PAL Question:

I have a 50-year-old Italian plum tree. The limbs have oyster-shaped growths on them. These growths will not come off--they are hard. Is it a fungus or disease? Or is the tree just getting old?

View Answer:

Hard fungal growths on trees are called conks, a type of bracket fungus, and they are not a good sign. According to The Sunset Western Garden Problem Solver, these growths "indicate a hazardous condition from decay inside." Usually by the time they are seen, decay inside the tree is substantial and you may need to get an arborist's help to keep the tree from breaking and dropping branches, and to assess whether it is a danger to structures or people. The Pacific Northwest Chapter of the International Society of Arboriculture provides a listing of local certified arborists. You can also get an arborist referral from Plant Amnesty.

Season All Season
Date 2010-02-26
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Keywords: Rosa, Fungal diseases of plants, Pesticides and the environment

PAL Question:

I heard somewhere that the fungicide Rose Pride was less toxic to beneficial insects than plain baking soda. Is this true? I'd like to continue to use it in my garden.

View Answer:

Rose Pride is the chemical Triforine. I was not able to find any articles which suggest it is safer for beneficial insects than baking soda. Pesticides Action Network's Pesticides Database indicates it is toxic in varying degrees to some forms of aquatic life. It is on the PAN List of "Bad Actor" pesticides, which means it belongs to a group of pesticides classified as most toxic (because they are known or probable carcinogens, reproductive or developmental toxicants, etc.). The Extension Toxicology Network also has a profile for this pesticide. Here are excerpts:
"In the United States, triforine is marketed for use on almonds, apples, asparagus, blueberries, cherries, hops, ornamentals, peaches and roses. Triforine is a 'restricted use' pesticide (RUP) with an EPA toxicity classification of I (highly toxic). Check with specific state regulations for local restrictions which may apply. Products containing triforine must bear the Signal Word 'Danger' on their label.
Triforine and the formulated product Saprol are considered of low hazard to honeybees and to the predatory mite Typhlodromus pyrii. It is also of low hazard to earthworms at recommended dose rates."

My comment would be that "low hazard" is not the same as no hazard, and since there are many other areas of concern with this highly toxic product, it would be best to find an alternative. Locally, the Woodland Park Rose Garden converted a pesticide-dependent landscape to an organic one, and the roses look better than ever.(See an article about the garden from the Seattle Times.) Many gardeners are learning to live with a bit of black spot on their roses, and manage the disease by maintaining good garden hygiene. Don't leave fallen leaves on the ground. Give your roses good air circulation, and keep the leaves dry when you water your plants. Mulching with wood chips can help, too, since they may prevent water from splashing up onto the leaves.

When deciding whether to treat a garden problem with pesticides, the "Precautionary Principle" provides an important perspective:
"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically."

Season All Season
Date 2010-02-27
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Keywords: Failure to fruit, Fruit trees--Cross-pollination, Pyrus, Fungal diseases of plants

PAL Question:

I have a 'Rescue' pear which has gotten pear rust. It is about 3 years old. I also have an 'Orca' pear tree that so far this season does not have rust. Last year we had terrible rust. We thought maybe it came from a secondary host, because there were Juniper bushes. Now those bushes are all gone and I did clean up the leaves from last year to try and avoid contamination from the rust.

Also, I have never gotten any pears on either tree. The Orca tree is a bit older, about 5 years old. They both were bought from Raintree Nursery.

View Answer:

Sorry to hear about your pear with rust, and about the lack of fruit. Washington State University's HortSense website says there are two types of rust that affect pears in our area:
"Two pear rusts which occur in Washington are Pacific Coast pear rust and pear trellis rust. Both require an alternate host. The rust fungus causing Pacific Coast pear rust is also found on hawthorn, apple, crabapple, serviceberry, quince, and mountain ash. The alternate host is the incense cedar (Calocedrus decurrens), which develops witches' brooms. Infected fruits of pear are deformed and drop prematurely. On the surface of the fruit, yellowish spots with cup-shaped pustules develop. Leaves and green shoots may also be infected. Symptoms are most obvious after flowering and before July. Pear trellis rust may also infect pears, causing reddish to orange blotches on leaves. The alternate host is juniper, which develops elongate, swollen galls along branches."

The only controls they recommend are cultural:

  • Avoid susceptible varieties such as 'Winter Nelis'.
  • Collect and destroy fallen fruit beneath trees.
  • Plant resistant varieties such as 'Bartlett'.
  • Prune out and destroy rust-infected tissues in pears and alternate hosts.
  • Remove alternate hosts in the vicinity of pear trees, when practical.

Here is an article from British Columbia Ministry of Agriculture and Food on managing this disease in the home orchard.

It sounds as if you are doing everything you can to prevent a recurrence. The web resource above also states that fungicide is probably not a worthwhile approach to managing rust on pears or junipers.

As for the lack of fruit on your trees, Raintree's pollination chart shows that 'Rescue' and 'Orcas' should cross-pollinate. It is possible that the 'Rescue' pear is not mature enough, or that its bout with disease slowed it down. Here is an article about failure to produce fruit, from MSU Extension. It mentions possibilities such as immature tree(s) and frost damage to flower buds.

I have an 'Orcas' growing without other pears in the garden, and yet it produces fruit, so I wonder if something else may be happening. Do you have a good number of bees and other pollinators in your garden? Do you or nearby households use pesticides that might interfere with pollinators? Here is information on protecting and encouraging pollinators, from U.S. Fish and Wildlife.

I also recommend contacting Raintree to see if they have any advice.

Season All Season
Date 2010-05-01
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Keywords: Soilborne plant diseases, Fungal diseases of plants, Verticillium, Maple

Garden Tool:

Verticillium wilt is making an appearance now as trees and shrubs begin to leaf out. Maple trees are especially susceptible. The sudden wilting and death of one or two branches in an otherwise healthy looking tree is the one obvious symptom. If this soil- borne disease attacked early in spring, tree branches may not have leafed out at all. Cutting into an affected branch typically reveals dark streaks. Control is difficult, but sometimes a tree can be preserved for a few years by cutting out the diseased wood and eliminating environmental stress such as drought. Make sure to disinfect pruning tools between cuts to avoid spreading the fungus. No fungicides for verticillium are registered for homeowners in Washington. For more information read Washington State University Cooperative Extension online article.

Season: Spring
Date: 2007-05-23
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Keywords: Fungal diseases of plants, Solanaceae (Potato family)

Garden Tool: Information on trendy colorful potatoes is available from Oregon State University. If we have a cool wet growing season watch out for the dreadful Late Blight! Read about how to control this fungal disease from Pacific Northwest Plant Disease Management Handbook.

Season: All Season
Date: 2003-03-19
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December 12 2014 11:33:49