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May
18, 2006
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: The leaves on my
petunias are turning yellow and drying up. This happens every year. They
are in planters or hanging baskets. The plants get fed about every two
weeks with Miracle-Gro. Is there something I can do to stop this? The
problem starts at the bottom of the plants and by midseason about half
of the leaves are gone, but still producing flowers. I have asked several
garden centers what might be causing this problem, but they have no idea.
I have purchased a liquid to mix in my sprayer to stop mildew and mold
spores, but that hasn't helped. I have tried spraying the plants with
a mixture of milk and water, but that hasn't helped, either. (e-mail reference)
A: Could they be
planted too deeply or in too much shade? Are you using pasteurized potting
soil? Are the hanging baskets free-draining? These are all the reasons
I can think of as to why the leaves are turning yellow. Otherwise I
have no idea what the cause may be.
Q: I have Colorado
blue spruce that I planted along with another one about 20 feet away last
spring. One of the trees looks very ill. Many of the needles at the ends
of the branches are brittle and falling off. The other tree is fine. Both
have the same exposure. I have started watering the trees every two weeks.
Could it be that I am watering too much? What is the best watering plan
for these trees? (e-mail reference)
A: The problem could
be that the tree is planted too deeply, has too much mulch around the
base, suffering from borer activity or the rootball dried out at planting
time and never recovered.
You are about right on with your watering plan, but don't make the soil
continually soggy.
Q: I read an article
on pruning clematis, but I’m not sure the advice is appropriate
for the Fargo area. The author wrote that no matter where you live, it
is best to let your clematis stay unpruned and dormant until spring. If
you have a plant such as a jackmanii, you should then cut the entire plant
down near the ground. Do I need to prune above a pair of leaves? I would
appreciate any advice you can give me. (Fargo, N.D.)
A: The advice you
read is probably something that the author has done every year with
good success. However, there is plenty of clematis that never gets pruned
until this time of year, but still does OK. The Jackmanii group blooms
on new wood, hence the advice to cut the plant down to ground level,
which assumes the owner wants blooms to that extent. Otherwise, cut
them where you wish. They will bloom on the new wood produced.
Q: We had some willow
and cottonwood trees cut down this spring. I would like to know what the
best method is to kill the sprouts. Removing the stumps is not an option
right now. (e-mail reference)
A: Spray any sprouts
that come up with Roundup. Drill holes in the stump and fill them with
saltpeter.
Q: My daughter works
for a florist and gave me a large plastic bag filled with peace lilies
in pots. We were in the process of getting ready to move, so I left them
in the plastic bag for about three months before I got to them. The tops
are brown, but most of the bulbs are still green. I want to set them out
at our new house, but we haven't finished building it. How should I store
the bulbs until I am ready to plant? (e-mail reference)
A: Store the lilies
in a cool, dark and dry place. I would suggest dusting them with powdered
sulfur until you can get them planted.
Q: I have a problem
with one of my African violets. It is a large, double pink violet. It
has white spots on the leaves. It is not in direct sunlight and I don’t
get water on it when I water. I have 12 other violets (different varieties)
that don’t have this problem. Can you help me? (Garrison, N.D.)
A: If it bothers
you, move the plant away from the direct sunlight and snip off the affected
foliage. I don't believe it to be a disease, just a reaction to the
direct sunlight.
Q: Our weeping willow
has several round bulges/ knots in various places. Some are an inch or
so across, others are about 3 inches. (e-mail reference)
A: Those bumps or
bulges could be cysts formed by insects or midge having laid eggs at
the trouble spots. The eggs cause cell proliferation in the tree, which
surrounds the developing larvae. Cut a bulge open and see what it contains.
Usually, this is nothing to worry about.
Q: Our healthy and
vigorous little leaf linden is being attacked by squirrels. The squirrels
are peeling and stripping the bark. How do we deal with this problem?
Will the squirrels permanently damage the tree? (e-mail reference)
A: Whatever possesses
these little varmints to do this at certain times is beyond me. While
such activity is not going to do the tree any good, I doubt it will
kill the tree, but I wouldn't put up with it. If you can, purchase a
product called Squirrel Control. It can be purchased on the Web at www.critter-repellent.com/squirrels/squirrels-in-my-trees.php.
I cannot attest to the efficacy of this product, so the best course
of action may be live trapping. Call your local Department of Natural
Resources office and see if it has any traps you can rent or borrow.
After trapping, move the squirrel to another location where it won't
be as destructive.
Q: I am from Charlotte,
N.C., but now living in North Dakota. I would love to have a magnolia
tree, but there is not enough love here in zones 2 and 3 to keep it warm
and alive! I would like to inquire on the viability of a dogwood or cherry
tree. How about wisteria? If you have any suggestions on any plants/shrubs/trees
that are from the southern region that may work here, please pass them
along. (Bismarck, N.D.)
A: What a change,
from Charlotte to Bismarck! Welcome to our fine state, even if it isn't
as warm as your former address. The pagoda dogwood might grow in Bismarck
in a protected location. The recent introduction of the snow mantle
dogwood by our woody plants researcher, Dale Herman, also may work for
you. The chokecherry is the only tree form that can grow in North Dakota,
but we are finding out that it is susceptible to black knot fungus,
which debilitates the tree. Wisteria is too marginal to recommend for
our region, but clematis vines do beautifully in most landscape situations.
Go to www.ext.nodak.edu/extnews/hortiscope/tree/treecntnts.htm
for a list of trees that you may want to consider.
Q: We bought our new
house three years ago and planted raspberry plants. On the other side
of the fence are four spruce trees belonging to our neighbor. I've heard
of a raspberry fungus that can affect pine or evergreen trees. Now I'm
worried that I need to dig up the raspberry bushes to not pose a threat
to our neighbor’s trees. What should we do? We can live without
the bushes and I'd feel awful if our neighbor's beautiful spruce trees
died due to fungus. (e-mail reference)
A: Don't worry.
Spruce trees are capable of defending against anything that raspberries
can catch as far as fungus or other pathogens. While there are some
common maladies that can affect broad populations of plant species,
they are not common. The pathogen that will attack spruce usually will
not attack raspberries because they are two different plant families.
Enjoy your berries and your neighbor's spruce!
Q: I have gall on
my Colorado spruce. I'm impressed with your knowledge and look forward
to your helpful response. Thank you. (Saint Paul, Minn.)
A: Thank you. I'm
glad somebody is impressed! It comes from living so long and enjoying
the subject matter. Those growths are probably cooley gall aphid galls,
which in reality are adelgids. These are pin-head size insects that
hide on the underside of the branch near buds. When the new growth begins
in the spring, these insects swell upon feeding on the new growth by
sucking the sap out of the needles. At the same time, they inject in
their saliva a substance that behaves like a growth regulator. This
causes plant cells to swell and enclose the insects, which gives them
protection from predators and any sprays. At the end of the spring season,
the galls dry and then crack, which allows the aphids to crawl out onto
the needles. The insects then go through another molt. Wings appear
and the aphid flies off to another tree. This time it is a Douglas fir,
where no galls are formed when the insects feed on the fir’s foliage.
The damage is mostly cosmetic, so no controls are necessary. Cutting
the galls off will not control the insects because they already have
departed. Removing the galls by pruning is a choice the homeowner makes
for aesthetic concerns. If control is desired, spray the underside of
the branches with dormant or horticultural oil prior to bud growth.
Q: A friend of mine
gave me a leaf of a plant she had. She instructed me to stick it in dirt
so it would grow. The plant has done extremely well, but I don't know
what it is! She told me she thought it was a cathedral plant, but all
my searches for such a plant have come up empty. The plant reminds me
of a Christmas cactus, but instead it has long "branches." From
the branches come leaves that are long and sort of notched, such as a
segment of a Christmas cactus leaf. It's supposed to bloom, but mine has
not. I don't remember what kind of flower it's supposed to have, but I
think she told me the flower is supposed to come off the leaf. If you
could give me any ideas as to what this plant might be, I'd really appreciate
it! It appears to have spider mites. I have used a cotton ball and some
rubbing alcohol to remove them, but now they are back. (e-mail reference)
A: This sounds like
a close relative to the Christmas cactus, which is epiphyllium, but
I cannot be sure. Spider mites are best controlled with a blast of cool
water because they hate it. After the weather gets nice for the season,
summer the plant outdoors to allow natural elements to get to it. Summer
it on the north side of your house.
Q: I just received
a prairiefire flowering crab tree. It is about 8 feet tall, but is in
the same bucket as when it was purchased. It has started to flower profusely.
When is the best time to plant this tree in the ground and what is the
best way to do it? (e-mail reference)
A: Get it planted
as soon as possible. If possible, hire a teen to assist you. An 8-foot
tree in a bucket is too much to handle, unless you are into weightlifting!
Dig the hole as deep as the container and twice as wide. Set the plant,
container and all, into the hole. Make sure the surrounding soil is
just even with the crown of the plant, which is where the stem becomes
the root system. After that, carefully cut the container off (I assume
it is a HD poly type), remove the sides, but leave the bottom on. Don't
worry about the bottom part. Backfill with the soil removed, firm by
hand and slowly soak the soil. Water it well once a week during the
summer.
Q: My daughter lives
on a farm near Milnor, N.D. She has a small tree in her front yard that
has hard, charcoal stuff on the branches. They have cut the branches off,
but then it just comes back on other trees the next year. Can you tell
me what it is and what to do about it? (e-mail reference)
A: I'm going to
make some assumptions, which are that the tree is deciduous, it is a
chokecherry, and black knot fungus is infecting it. This is a difficult
disease to control once it has become established. My usual advice is
to get rid of the tree rather than continually fight it. Lime sulfur
applied in the early spring before leafing is a control measure. Apply
a Bordeaux mixture when it leafs out. These sprays are most effective
when used as a preventative, not a cure.
Q: Two years ago we
bought a house with a beautiful silver maple in the backyard. We needed
to put an addition on the back of the house and took extra care to try
to protect the tree. We laid down 24 inches of mulch to protect against
construction traffic. The tree seems healthy, but I have noticed this
spring that a few smaller branches are without buds. What should I be
watching for to make sure this tree stays healthy? Is there anything I
should do to help it along? (e-mail reference)
A: Look for major
branch decline, which is called crown decline or dieback. Get a core
aerator and aerate your entire lawn area where the tree is planted.
This will help get air to the roots in case the soil was compacted during
construction.
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Source: Ron
Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
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