managing black spots on roses

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

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.

diseases affecting English laurels

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.

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.

managing mummy berry on blueberries

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.

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.

yellow houseplant mushroom called Leucoprinus

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.

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.

Michael Kuo’s website, MushroomExpert.com has information about Leucoprinus. 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.”

diseases that affect peony plants

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.

Garden Tip #34

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.