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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Powdery mildew and Euonymus

Have you heard about a problem with Burning Bush
(Euonymus alatus) getting a mildew this year? The
leaves have turned yellow green with small spots of
lighter yellow discoloration.

 

Powdery mildew is a common and usually not life-threatening
problem with Euonymus. Make sure the plant has good air
circulation, and be sure to clean up and destroy fallen
leaves which are infected. However, the symptoms of this
fungal problem would be whitish coating on the leaves, rather
than yellowed leaves. This makes me wonder if it is a
different problem such as scale (which is actually an
insect). Check and see if there are small bumps on the leaves
or stems. Scale can cause yellowed leaves. If your plant has
a small infestation, you can try scraping the scales off with
your fingernail, prune out the most infested parts of the
plant, and then apply dormant oil to the trunk and branches
before growth starts next spring, or apply superior oil
during the growing season. There are also other fungal and
bacterial problems that could be causing the spots.

See this fact sheet from Penn State for more on Euonymus scale.

Here is an archived link to additional information, which comes from
University of Illinois Extension. Excerpt:

Burning bush (also called Winged Euonymus): Euonymus alatus

Cold injury – Winter injury may be caused by very low
temperatures as well as drought stress. With excessively low
temperatures, the moisture in the cells freezes (due to
chemical compounds in plants, moisture freezes at various
degrees below freezing). Drought stress already has resulted
in limited moisture in the plant cells. Dry, freezing winds
during the winter reduces the moisture level even farther,
often resulting in dead plant tissue. Diseases can help
magnify or increase susceptibility to winter kill. Nectria
canker kills the sapwood tissue thus reducing or even cutting
off moisture to tissue further out on the plant. Winterkill
also makes plants more prone to infectious diseases and
insect problems.

Dieback/canker – See bridal wreath spirea. In addition
Botryosphaeria dothidea will infect and kill for similar
reasons.

Winged euonymus scale – Lepidosaphes yanagicola occasionally
occurs in the southern half of Illinois on burning bush. It
is an armored scale. And will attack several trees as well.
This scale can cause premature leaf drop, branch die back and
cause the plant to become more prone to winter injury. It is
found between the “wings” – the bark ridges. It does not move
to the plant’s leaves. The scale over winters as an adult and
lays its eggs in June. Eggs may be laid for up to a month.
Mating occurs before frost.

Euonymus scale – Unaspis euonymi – females are black and
males are white. The scale causes the foliage to develop
yellowish green spots. Heavy infestation results in early
foliage drop and often stems are killed. Eggs survive by over
wintering in the female body. The eggs hatch about early June
in Northern Illinois. Crawlers emerge and move onto new
growth or can be blown by wind to other plants.

Since I cannot diagnose the problem remotely, it makes sense
to take plant samples to a Master Gardener Clinic.

growing Allium from seed

Could you tell me how to grow Allium from seed?

 

I will assume you are propagating ornamental Allium. According to the American Horticultural Society’s Plant Propagation (edited by Alan Toogood; DK Publishing, 1999), Allium seeds may be sown any time from late summer to early spring. Seeds should be collected when the flower heads turn brown and before the seedpods open. If you tug gently on the flower stalk and it comes away easily from the base, the seed is ripe. Cover the spot where the stalk was removed with soil to prevent entry to pests. With smaller flowering Allium, you can shake seeds directly into a paper bag (without removing stalks). Sow the seeds fresh, or store them at 41 degrees F, and sow in the spring. Germination time is usually 12 weeks, but in some cases it will take up to a year.

The Royal Horticultural Society says that Allium cultivars may not come true from seed, so you may want to consider alternate methods of propagation, such as by offsets or aerial bulbils.

pruning and training Wisteria

Is it all right to cut off the hanging pods from the Japanese
Wisteria? Will cutting them have any adverse affects to blooming next
year? Some are hanging so long that we keep walking into them! Maybe I should cut them and bring them inside for decoration.

 

Cutting off the seedpods on your Wisteria is not a problem, just be
careful not to cut the stems back too far (unless you are intending to
prune, which you can certainly do if you need to control growth) as there
may be buds further up which will be next spring’s flowers.

Fine Gardening online has a helpful illustrated article on wisteria pruning which includes the following:
“Some seedpods may be left on the vine for winter interest, but just know that if you bring them inside, warm temperatures will cause them to explode.”

You may find the following links to general information on care and
pruning of Wisteria helpful:

 

 

Excerpt from an article, “Pruning Vines,” by Donald Hodel and Dennis Pittenger:

Pruning wisteria extensively during the dormant season may
encourage rampant vegetative growth the next spring.
Instead, in July prune out the long, straggly growth
except those branches needed for climbing. This is more
likely than anything else to induce flowering. Shoots
should be cut back one-third to one-half their length.
This will induce them to produce the short spurs that will
bear next season’s flower clusters.

diagnosing rhododendron problems

The edges of the leaves on one of my rhododendrons are turning brown and
crispy. This condition advances toward the midline until the leaf dies. My older, more established rhododendrons are looking fine. All have flowered this spring.

 

We can’t diagnose the problem via e-mail. However, what you describe could be a couple of things.

It might be marginal leaf necrosis which can be caused by cold damage, and made worse by wind and drought; by drought while the plant is in active growth; by high
amounts of salt in the soil, often due to overuse of soluble fertilizers,
and seen often if plant is located close to the house, where the eaves
prevent rainwater from reaching the soil. Other causes are poor drainage,
planting too deep, root damage, root weevils, nutrient deficiency, or
disease. (Source: How to Identify Rhododendron and Azalea Problems,
Washington State University Cooperative Extension, 1984).

There are descriptions and illustrations of rhododendron problems on the HortSense website of Washington State University Extension.

For comparison purposes, see the lists of diseases and problems affecting
Rhododendrons from University of California, Davis Integrated Pest Management Online. To get a definitive answer, it may be a good idea to take samples of the
affected leaves to a Master Gardener Clinic for diagnosis.

groundcover plants for walkways

I am building a stone walkway. What can I plant in the cracks
that will take the sun and that I can walk on?

 

Creeping thyme would be ideal for your needs. It will do well in sun, and
can withstand foot traffic. Colorado State University Extension has useful information on groundcover plants for dry conditions.

Leptinella, or brass buttons, is another option.

Chamaemelum nobile likes sun and will withstand light foot traffic.

The website for Stepables, a company specializing in groundcover plants,
allows a search by plant characteristics.

ivy and other clinging vines

My question is about ivy for growing up a brick wall. What would you recommend? How do Boston ivy and English ivy compare for this purpose? We live in New Jersey.

 

First of all, it is important to know that clinging plants, such as
Boston ivy and English ivy have the potential to “damage old, soft mortar
and strip off pebbledash”. (Gardening with Climbers by Christopher
Grey-Wilson and Victoria Matthews) It is also suggested that these
vines have a “structurally sound surface and must be prevented from
reaching under house eaves and roof tiles and into window casements.”
(The New Royal Horticultural Society Dictionary Manual of Climbers and
Wall Plants edited by JK Burras and Mark Griffiths)

The New Jersey Invasive Species Strike Team has a factsheet on both English ivy (Hedera helix)and Boston ivy (Parthenocissus).

In addition to taking this information into consideration, it would also
be important to identify the amount of sunlight and the extent to which
the side of the house will be exposed to harsh winter winds and
temperatures. Neither Boston nor English ivy is recommended for full
sunlight. Boston ivy will give you more fall color and interest and will
withstand cold winters. (Simon & Schuster’s Guide to Climbing Plants by
Enrico Banfi and Francesca Consolino)

If you want to consider an alternative vining plant, you might want to install a trellis. That way you will not have to rely solely on vines which cling to the brick. You could try Clematis or some the honeysuckle species that are native to the northeastern U.S. There are several listed in this article (now archived) by William Cullina, “Alternatives to invasive or potentially invasive exotic species,” from the New England Wildflower Society:

  • Lonicera ciliosa (Orange Honeysuckle)
  • Lonicera dioica (Limber Honeysuckle)
  • Lonicera flava (Yellow Honeysuckle)
  • Lonicera sempervirens (Trumpet Honeysuckle)

ornamental grasses that tolerate salt water

What ornamental grasses can I plant near salt water, and is there a local nursery that specializes in grasses?

 

As far as nursery sources, I think a full-service nursery is your best bet for finding ornamental grasses. The only “specialist” in grasses I could find is Walla Walla Nursery, which seems a long way from Seattle to go.

King County’s interactive native plant guide also includes a page on marine (salt water) shoreline plants. At the bottom of the page, note the three native grasses which are recommended:

  • Lyngbye’s sedge (Carex lyngbyei)
  • tufted hairgrass (Deschampsia cespitosa
  • dunegrass (Elymus mollis)

The following list of plants according to their salt tolerance comes from University of Minnesota Extension (link no longer available), but there may be some ornamental grasses that will do well here.

From the lists:

  • Calamagrostis acutifolia ‘Karl Foerster’ (Karl Foerster reed grass): high tolerance
  • Schizachyrium scoparium (Little bluestem): high tolerance
  • Elymus arenarius (Blue Lyme grass): high tolerance
  • Pennisetum alopecuroides (Fountain Grass): high tolerance
  • Festuca ‘Elijah Blue’ ‘Elijah Blue’ fescue: moderate tolerance

In her book Gardening at the Shore (Timber Press, 2006), Frances Tenenbaum lists a number of ornamental grasses (in addition to dune grasses):

  • Festuca glauca
  • Miscanthus sinensis
  • Muhlenbergia capillaris
  • Stipa tenuissima [now renamed Nassella tenuissima–in my experience, this grass is aggressive, seeding itself everywhere; the seedheads stick to people and pets who walk past it]

There are many attractive cultivated varieties of some of the plants listed above, and most local nurseries will carry them.

common tomato problems and diseases

I was just outside checking on the slow ripening progress of my
tomato plants and noticed something that has me concerned. There seems to be a fungus or mold at the very base of my “super fantastic” tomato plant.
Other than this issue and the slow ripening the plant seems to be
doing okay. I haven’t noticed this fungus/mold before so I don’t know
if has just appeared and is spreading rapidly or if it has been
there all along. Do you know what it is? Will it spread through
the entire plant? Will it spread to the other tomato plants and
veggies in this bed? Should I remove the entire plant?

 

This sounds a lot like Fusarium wilt, but it could also be Verticillium
(another fungal problem) or even walnut toxicity (do you have any black
walnut trees within 50 feet of your plants?). It might even be excessive
watering which is causing the problem.

According to The Organic Gardener’s Handbook of Natural Insect and
Disease Control edited by Barbara Ellis (Rodale, 1996), you can cut open
a stem near the soil line and look for internal discoloration.
Verticillium affects the whole plant, while Fusarium will start by
infecting individual shoots and then spread. Tomato Fusarium only affects
tomatoes, while there are numerous plants which are susceptible to
Verticillium. The best thing to do if your plant is suffering from these
fungal diseases is to destroy them, so you may want to take a sample to a
Master Gardener Clinic for diagnosis before you do anything drastic.

General resources on tomato problems:

Recognizing Tomato Problems from Colorado State University Extension.

Vegetable MD Online from Cornell University.

University of California, Davis Integrated Pest Management has
excellent pictures of the insides of the stems, for comparison.

early leaf coloration in vine maples

We planted a clump of vine maple last fall and because we were in a hurry (landscaping a new home), we just put in without amending the soil. It is dealing with extremely sandy soil, though we did give it fertile mulch, and gets full sun all day long. It looks okay, but the leaves have been very red all summer, basically what I would expect it to look like in the fall. We’ve been watering a lot to make up for the sand. What’s the story on vine maples? We had a lot of them at our old house, but they were mostly under fir canopies or at least were not in full sun. Any tips on helping this one out?

 

I wonder if the leaves on your Acer circinatum are evenly red, and if they look scorched at all. Leaf scorch is a problem for maples in conditions of stress.
See this information from the HortSense database of Washington State University. Excerpt:

“Leaf scorch on maple has many possible causes. Plants that are under
stress, such as drought or heat stress, may not provide sufficient water
to the leaf margins, causing the edges of the leaves to turn brown and
dry. In some cases, scorch may spread to areas between veins or entire
twigs may die back. Trees placed near heat-reflecting surfaces, such as
buildings or pavement, often suffer from heat stress. Excessive salts
from overuse of chemical fertilizers may cause leaf scorch. Scorch may
also be a symptom of damage to the roots or stem.”

If the leaves are not scorched in appearance, it is possible their early
coloring is the result of some other type of stress, or perhaps the leaf coloration has to do with their being in full sun, in an exposed site. You may find this information from University of British Columbia Botanical Gardens (no longer available online) interesting: “The formation of red pigments in the autumn provides protection, preventing the too-rapid breakdown of chlorophyll which could occur in exposed (read: excess light) areas. As you can clearly see in the leaf in the upper right, the bottom-right corner has the pattern of the leaf above. Where the leaf above shaded this leaf, no red pigments were produced. Where the leaf was exposed, bright red anthocyanins were formed. To take this to a broader perspective, vine maple trees in shaded forests and under low light conditions have little need to produce red pigments, as the breakdown of chlorophyll can occur at a modest pace. However, vine maples in exposed sites turn flame orange and red, so that the pigments produced will slow the rate of chlorophyll breakdown.”

An article (no longer available online) from Minnesota Department of Natural Resources discusses premature fall color in maples. Excerpt:

“Each August brings a few trees that begin the fall color frenzy ahead of
schedule. In addition to signaling the change of seasons, these trees are
sending a clear signal that they are suffering from some form of stress.
Stress can have a wide variety of causes, be mild or severe, or, benign
or fatal. In any case, professional tree ‘care givers’ should be aware
that the trees are talking to you. Are you listening?
“Maples are probably the group of trees that most commonly exhibit
premature fall color. Sensitive to changes in their environment, maples
commonly show early color in years when summer rains are heavier than
normal and raise soil moisture to or above field capacity during the
period from mid to late summer. The maples that show this characteristic
the best are the several species of soft maples (silver and red) that
commonly inhabit the shrubby areas around wetlands. These trees commonly
begin to show deep, rich purples as early as the first week in August.
Maples in communities also commonly display early color due to stress
mechanisms more common to the urban environment. Sugar maple, in
particular, shows early color due to the stress induced by infection from
Verticillium wilt. This disease may occur in nursery grown stock in
commercial trade. It is difficult to detect because it is soil-borne,
difficult to culture, and commonly not tested-for in the nursery. In
addition, Verticillium wilt is a relatively weak pathogen that does not
do well on young, vigorous nursery stock. Trees can be infected for many
years without showing external symptoms of the disease. When they do
begin to show symptoms, one of the first is premature fall color followed
in succeeding years by a progressive, if not slow, crown decline and
dieback.”

Maples in communities that are planted ‘just-a-little’ too deep often
show premature fall color. Again this is more pronounced in years with
wet summers. The likely mode-of-action is decreased soil oxygen content.
Planting too deep ‘smothers’ roots reducing oxygen in the root zone. So
does over watering whether natural or artificial. The bottom line is
stress-induced premature fall color. Remember that stress is (1) caused
by many factors, (2) cumulative, and (3) potentially fatal if left
untreated.