on pruning pin oaks

I have a big pin oak that needs to be pruned. Maybe 1/3 of the leaves have dropped. Is this a good time to prune or should I wait a week or two?

The American Horticultural Society’s Pruning & Training (DK Publishing,
1996) says to prune pin oak (Quercus palustris) as you would white oak,
that is, when the tree is dormant, in winter or early spring. Pin oak
can be trained as a central-leader standard, but if this is a mature tree
which was not trained this way, do not attempt it now. Established trees
should not need much pruning at all, so only prune what is dead,
diseased, or damaged, or any branches which are drooping, in order to
provide clearance.

The Sunset Pruning Handbook (1983) says the following:
“Pin oak is a pyramidal tree when it’s young. It forms a rounded top as
it matures. during the pyramidal stage, its lower branches are
down-sweeping. If you remove the lowest branches to gain walking space
beneath the tree, the limbs above will bend into a down-sweeping
position. When the tree is mature, the down-sweeping process will stop.
You can then cut off lower limbs to create a tree suitable for walking
under.”

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 brown rot on ornamental cherry trees

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

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.

Dracaena plant culture and care

I inherited a Dracaena from a co-worker. She had it for 4
years and it stayed nice and dark green the whole time, but it never
grew. I’ve had it a little over 6 months and it has almost doubled in
size. The trouble is that all the new leaves have lighter green streaks
and imperfections in them. I water the plant once a week, following my
co-worker’s instructions, letting the soil dry out on top. The plant is
about 7 feet from a window that is covered with blinds, so it gets its
light mainly from the ceiling fixtures which are 12-15 feet up. Any idea
what I’m doing wrong?

The most common problem with Dracaena is usually over- or under-watering.
Also, this plant is very sensitive to fluoride. Some varieties naturally
have variegated leaves, but if your plant used to be dark green and now
is not, that can’t be the reason. Dracaena needs moderate to bright
indirect light, temperatures of 65-75 degrees, and fertilizing every 2
weeks in spring and summer (balanced fertilizer), monthly feeds in the
fall. Keep lightly moist but do not over-water. According to The Complete
Houseplant Survival Manual by Barbara Pleasant (Storey Publishing, 2005),
pale leaves with faded variegation patterns signify too little light or
not enough fertilizer. In some office situations, plants may need
fertilizer every 2 weeks year-round. You may need a brighter site, as
well. If, however, you would describe the leaves as droopy and yellow,
that could be a sign of root rot from excess water (although I doubt
that’s it, since you have been letting it dry out between waterings.
Check anyway that the plant never has standing water at its base). Mature
plants can be re-potted every 2-3 years, and it sounds like your plant
might need a larger pot. The fact that it grew so tall so quickly almost
makes me think it’s striving for the light.

Clemson University Extension has a guide with general information on the care of this plant. To be certain of what the problem is, you might want to take pictures and bring sample leaves to a Master Gardener Clinic.

overwintering Datura and Brugmansia

I have a purple Datura that I grew from seed. Do you have any suggestions on how best to overwinter this plant? Basically I have found some contradictory information online but some of it suggests cutting down this year’s stalk (which seems a little drastic but I make no claims of being an expert). Any information you might have would be most appreciated.

Do you know for certain which genus and species your plant is? It sounds
like it could be Datura metel, which is grown as an annual. Datura
blossoms point up or outward, while Brugmansia is shrubby, and its flowers hang downward.
Some Brugmansias will overwinter in the Seattle area and are
semi-evergreen or evergreen. Others may die back to the ground and come
back in the spring. They are longer-lived than Datura. Datura is more
likely to act like a perennial or annual.

If you are growing an annual Datura, the best thing to do is save
seed from the fruit capsules in summer. Exceptions are Datura wrightii
and Datura inoxia, which can overwinter. In warmer winter climates, these
can be covered in the fall with twigs, straw, or pine needles. Growth may
resume in March or April. In colder winter climates, you would need to
overwinter the fleshy rhizomes in a container, covering them with earth.
Keep the container in a cool, dark garage or cellar. Expose the
rhizomes to temperatures of 53-64 degrees and daylight beginning in
March. This is much more difficult than simply planting new seed each
year, but plants which sprout from rhizomes grow faster and flower
better. (Source: Brugmansia and Datura by Ulrike and Hans-Georg
Preissel; Firefly Books, 2002)

problems affecting camellias

My camellia is potted and lives on an urban deck. In the spring, it was full of beautiful blooms and lush foliage. This summer it has been plagued with aphids and mealy bugs. I have sprayed two different times, 3 times each. My bush appears to continue to fail. It is dropping perfectly healthy-looking leaves and getting new growth, but it has few new buds and looks very “naked.” What is wrong with it? I have noticed small insects in the soil as well. I have added a watering of Safer-soap-with-water mixture but it seems to have had no improvement. Please help!

I wonder what kind of spray you have been using. Was it the Safer soap product?
Aphids seldom cause the demise of a mature plant. Aphids are attracted to lots
of leafy new growth, so it is best to avoid quick-release high-nitrogen
fertilizer. The best way to keep aphids in check is to encourage natural
predators like ladybugs, syrphid flies, lacewings, and parasitic wasps. Broad
spectrum pesticides will harm the helpful insects as well, so I would avoid use
of those. Mealy bugs are also a favorite of natural predators like those
mentioned above. Usually, regularly spraying jets of water to knock the aphids
and mealy bugs off the plant’s leaves should keep the damage in check. If
necessary, you can use insecticidal soap, but always test it on a small area of
the plant to make sure it does not cause any damage to the leaves.

It is possible there is something else going on with your camellia. Here is a
link to University of California, Davis’s Integrated Pest Management website,
with a list of problems affecting camellias. My own camellias do shed a certain number of healthy green leaves every year, but still manage to keep flowering. Excessive leaf drop may indicate overfertilizing, but it could also be a sign of too much or too little water.
Did buds drop from the plant, or did they simply not form? Failure to form buds
might be a result of cold injury (although since you had flowers in spring, this
seems to not be the problem), or it could also be a sign of overfertilizing with
a nitrogen-heavy product which encourages leafy growth at the expense of
flowers.

You may want to bring samples of the insect-affected leaves and the insects in
the soil to a Master Gardener Clinic for identification and diagnosis. You might
also mention the excessive leaf drop, which can be a symptom of Sudden Oak Death
(Phytophthora ramorum).

pesticides alternatives to control sod webworm

Our maintenance contractor has told us that our grass is infested with the dreaded sod webworm, and that we should attack it immediately with the insecticide Covert. A little research tells me that this product is very toxic. Question: true or false? What are some commercially available alternatives if this is a toxic product?

It would be best if you could avoid using pesticides to control sod webworm. If you can encourage natural predators in your garden (such as ants, ground and rove beetles, parasitic wasps, and particularly birds), this should cut down on the infestation, whereas pesticides may well have a deleterious effect on beneficial insects and wildlife. University of California, Davis Integrated Pest Management also suggest that reducing thatch, and proper irrigation and fertilization of lawns will cut down on infestations of sod webworm.

Covert is a synthetic pyrethroid (as opposed to a natural pyrethrin). You may have already looked at the
Material Safety Data Sheet for this product, but in case you have not
seen it, here is a link. This document lists the product as highly toxic to bees, extremely toxic to fish and aquatic life, and notes that it contains ethyl benzene, a confirmed animal carcinogen. The Northwest Coalition for Alternatives to Pesticides also has information about the toxicity of permethrin (an ingredient of Covert). Here is more on permethrin and pyrethroid insecticides. Essentially, synthetic pyrethroids last longer in the environment than pyrethrins. They may be less toxic than some pesticides, but they are not without health and environmental concerns. Since there are nonchemical methods of control, it does not make sense to take a chance using something which is potentially harmful.

Bt or Bacillus thuringiensis is registered for use on sod webworm, and you can find it as well as beneficial insects, Steinernema
nematodes from some gardening suppliers and well-stocked nurseries. Peaceful Valley Farm & Garden Supply has a large inventory of organic pest control products:

Organic Pest Control

Safer Caterpillar Attack

Parasitic Nematodes, Steinernema carpocapsae

Moth Egg Parasite – Trichogramma Wasp

I encourage you to pursue these alternatives to using the toxic product
suggested by the maintenance contractor. Toxic chemicals can harm birds
and beneficial insects, and using such products starts a vicious cycle,
since those creatures would actually help keep down the undesirable
webworm population.

managing encircling roots or stem girdling roots

I live in Wausau, Wisconsin. Our city planted small
maples two years ago near the street. They are now about 8-10 feet
tall. Both of ours show some encircling roots above the surface of
the ground under the mulch. The roots are about 1/2 inch diameter in one case
and a bit larger in the other. Is it too late to prune these
away? Any other suggestions?

The answer to your question will depend, to some extent, on the
type of maple tree you are growing. Silver maple will tolerate
root-pruning, but sugar maples are intolerant of it, and can be
more likely to break in windstorms if roots are pruned. There is
always some risk of loss involved in root-pruning a tree.
Source: Iowa State Extension.

Since encircling roots are not good for the tree, you probably will
need to prune, but it would be best to consult a certified arborist
in your area to make sure this is done correctly. University of Minnesota
has a guide (now archived) called “Stem Girdling Roots: The Undergound Epidemic Killing Our Trees” by Gary Johnson. Excerpt:

Removal is the most common treatment of encircling roots or SGRs
that have caused minimal stem compression. Roots may be removed
with wood gouges, saws, or pruners during the examination process.

When SGRs have caused extensive stem compression and are fully or
partially embedded in the stem, modify the removal treatment to
avoid damage to the stem. Embedded and severely compressing SGRs
are often left in place when they cannot be safely removed; there
is some belief that SGRs reduce the typically short life span of
urban trees by only a few years, and the potential damage
associated with SGR removal is not justified (Watson et al. 1990;
Tate 1981). A compromise is to prevent the SGR from growing and
further compressing stem tissues by severing it at the edges of the
stem. Remove the remaining root to a distance where it no longer
poses a threat to the stem and allow the severed SGR to decay with
time. Annual examination of the stem to assess for decay is
recommended.

The season during which SGRs are removed might influence the
success of the treatment. Smiley (1999a) found that summer removal
resulted in better diameter growth over two years than did fall
removal or a combination of summer and fall removal for red maple
trees under an irrigation system.

Regardless of treatment, do not backfill the examination area.
Lightly mulch the exposed roots but not the root collar flare or
stem area. Subsequent examinations will not require the
time-consuming removal of soil.

To find a certified arborist in your area, you can search your
local chapter of the International Society of Arboriculture.

removing pesticide residue from house plants

I just bought a Ficus lyrata that was heavily treated with pesticide. As the plant makes my eyes burn, how can I minimize the pesticide residues on the large leaves? Is the citrus-based Veggie Wash appropriate and not harmful to the plant, or is there a better solution? If changing the soil and pot is necessary, does Ficus lyrata like any particular soil?

Without knowing what pesticide(s) were used, it is difficult to say how the residues could be removed. Looking at The Complete Houseplant Survival Manual, I can see that you would do no harm to the Ficus lyrata by washing the leaves with a sponge dipped in soapy water and then rinsing them with fresh water (this is a remedy often suggested for spider mites). Ficus also tolerates insecticidal soap well, so I imagine that the citrus-based veggie wash would not harm the ficus either. Of course, if the plant is making your eyes burn, it makes sense to take precautions to protect yourself while you are working with it–wear safety glasses, gloves, and a mask, and don’t continue to work with it if it still bothers you.

Ficus lyrata is not picky about soil, any good potting soil will do, and it is
generally suggested that a smallish pot will help keep the plant from getting
too big.