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August
17, 2006
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: I have a white
flowering dogwood. It had very heavy, beautiful blossoms, but when the
leaves came out, they wilted. They were stunted as well. The tree gets
ample water. I did two things differently this year that may have affected
the tree. I put some Job fertilizer tree stakes in the ground in early
spring, before the leaves came out, and sprayed the lawn with Weed-Be-Gon
liquid weed killer. This also was done before the leaves came out. I was
careful not to get the canopy wet, but I did spray the lawn under the
tree and near the drip line. Could this have caused my problem, and do
you think the tree will survive? (e-mail reference)
A: The fertilizer
stakes are close to being useless. Research has shown that they do not
provide significant benefits to trees or shrubs. Most trees and shrubs
do not need supplemental fertilization unless they are in very poor
soil. The herbicide is the likely culprit because flowering dogwoods
are very sensitive to any kind of broadleaf herbicide. The active ingredient
in Weed B-Gon (2,4-D) is mobile in the soil. The 2,4-D could have been
taken up by the root system of the tree, resulting in the problems you
are witnessing. As to whether the tree will survive, only time will
tell. Just have a little patience.
Q: I have two beautiful
hydrangea bushes that yield big, gorgeous blooms. However, when I cut
them and put them in cold water, they wilt, droop and shrivel within 24
hours. Is there a trick to keeping them fresh? (e-mail reference)
A: For fresh-cut
flower arrangements, take long stems and strip off all the leaves. Cut
the bottoms of the stems under lukewarm water. Place the stems in water
up to the blossoms. It is helpful to finish by misting the flower heads
so they will absorb more moisture.
Q: I have two apple
trees. One tree is eight to 10 years old. It has produced apples every
other year for the past three or four years. I planted another tree within
75 feet of the first. I thought the new tree would help in the polarization
process (both are honey crisp trees). Do I need to spray these trees with
any chemical? If so, with what and how often? (Fergus Falls, Minn.)
A: If both are of
the same apple species, you shot yourself in the foot. A different species,
such as a sweet sixteen, would have been better. Also, I am against
spraying unless it is needed. I never spray my apple trees.
Q: Our two ash trees
in our south Fargo yard have developed a powdery, light-green funguslike
growth on some of the lower leaves. Some leaves are curling into a ball
shape that is sticky. Any thoughts? (e-mail reference)
A: Two thoughts.
It could be powdery mildew or likely some insect with a piercing-sucking
mouth part that is causing the foliage to curl. The mildew is not going
to be overly destructive, but the insect should be brought under control
if possible. Contact Kelly Melquist, a certified arborist, at (701)
729-6899 to set up an appointment. He is very busy these days, so I'd
be surprised if he could get to you in less than two weeks.
Q: Is a golden ash
suitable for the rainfall and alkaline soils of the Jamestown area? (e-mail
reference)
A: Not likely because
golden ash hardiness runs from zone 5 to 7. Besides, this species is
more susceptible to ash borer than the natives. Also, the fact the foliage
is yellow on new growth sometimes drives people crazy because they like
the green color. The same problem exists with the golden honeylocust.
It’s a novel idea, but poor in practical application. It does
tolerate alkaline soils and limited rainfall. Who knows? Perhaps with
continued global warming, Jamestown and the rest of the state south
of Interstate 94 might become zone 5!
Q: We have what I
believe is a twisted or corkscrew willow on our property. Sadly, the tree
seems to be dying. It has branches from the core that appear to be dying.
I love this tree. Is this a tree that should not be planted in our zone?
Our backyard does have underground sprinkling. Is this a problem? Do I
remove the tree and replace it? What would be a good replacement? (Saint
Cloud, Minn.)
A: The corkscrew
willow is hardy enough to grow in your area. The moisture content of
the soil shouldn't be a problem, but the direct impact of the water
from the sprinkler system could be the cause of the problem. You can
replace this tree with another one just like it, but have the irrigation
system checked out before doing so. If the water is spraying directly
onto the tree, have the sprinkler heads adjusted.
Q: Please tell me
if I can deadhead my irises and cut the stocks or do I have to let them
die naturally. (e-mail reference)
A: Deadhead the
iris flowers, but leave the foliage alone.
Q: We purchased a
Canadian chokecherry tree last year that looks great in our yard. Since
then, we have acquired a puppy and are concerned about the tree being
poisonous to the puppy. Do we have to worry about the dog eating the cherries,
leaves or any other part of the tree? Also, we plan to have children,
so we are wondering if this tree will be harmful to the kids. (e-mail
reference)
A: All parts of
the chokecherry are poisonous to pet and humans, except the edible flesh
of the fruit. However, poisoning cases are very rare and steps can be
taken to keep animals and children away from this and other trees and
shrubs that would fall into this category.
Q: I just moved into
a house that has two flowering crabs in the backyard (my mother told me
that is what they are). They both look OK from a distance, but when you
get closer, you can see little holes in the branches and bark. The holes
look like someone has drilled into the bark. There also are little eggs
on some of the leaves that ants are feeding on. I would like to know what
kind of bug this is and what I can do to stop it. (e-mail reference)
A: This sounds like
bark beetles, borers or possibly scale insects. You can send photos
if you wish or get a product called Bayer Advanced Tree and Shrub Insect
Control and use that as a drench around the base of the tree. The product
is translocated systemically through the vascular system of the plants,
killing the insects that may be feeding on the plants.
Q: I have an apple
tree in my yard that has been producing apples for about 10 years. This
year, I noticed some leaves were turning black. After the leaves get infected,
the whole branch (leaves and branches) turn black and look rotten. I've
cut a few branches off to try to stop this unknown problem, but to no
avail. I have another apple tree in my yard that’s doing fine. Any
help would be much appreciated. Thanks. (e-mail reference)
A: This is probably
sooty mold that is the result of aphids or mites feeding on the leaves
and new growth. Their honeydew causes a saprophyte to form under certain
conditions. This causes the disgusting, sticky and sometimes smelly
mold on the leaves and branches. Treat the insect or mite and the mold
will disappear. Left unchecked, the mold will cause the tree to decline
and eventually die from insufficient photosynthetic activity.
Q: Your Web postings
are very helpful. Is there a spray that I can use to kill grass in my
ornamental poppies and peonies? Also, my hollyhocks seem to get brown
leaves from the bottom up. Lastly, my petunias never seem to bloom profusely
and last the summer. Any suggestions? Thanks for your help. (e-mail reference)
A: Glad you find
the postings useful. It would help me if you could give me a better
description of where you live and what the site is like. Is the area
shady or sunny? What is the moisture content, wind exposure and soil
type? What type of cultural practices do you use? I do have some answers
based on what you have told me. Hi-Yield Grass Killer is a common product
on the market that contains sethoxydim. If you cannot find that particular
brand, then check any grass killer brand on the market that has sethoxydim
as the active ingredient. Hollyhocks are wonderful hosts to a plethora
of fungal diseases, but I don’t know which one you are referencing.
Protective fungicide sprays are needed to keep the fungal diseases in
check, before any symptoms show. I suggest hand removing the symptomatic
foliage and spraying the rest of the plant with a locally available
fungicide. Petunias need full sunlight, plenty of moisture and ample
fertilization in well-drained soil in order to show their best.
Q: I have just discovered
what look like tiny marshmallows on my maple trees. They are sticky. What
is this? (e-mail reference)
A: You are being
plagued by the same insect pest that we have in our area, the cottony
maple scale. What you are seeing is the adult female producing her egg
sac, which has some 1,000 to 1,500 eggs. The eggs are or soon will hatch
the scale nymphs, which are about the size of a period at the end of
a sentence. They will migrate to the foliage, insert their stylets into
the underside of the foliage and begin feeding. The result of this massive
feeding is the production of copious amounts of honeydew secretions
from the insects. They then will migrate down onto the woody stem tissue
just before leaf drop and cover themselves with a dark scale for the
winter. These will be fertilized females that will produce egg sacs
next year and repeat the cycle. The best control we have been able to
recommend is the use of a product called Advanced Tree and Shrub Insect
Control, which is a systemic insecticide that is applied as a soil drench
around the trunk of the tree. The material then is translocated throughout
the vascular system of the tree and kills the feeding insects. It is
supposed to have a longevity of 12 months after application.
Q: I enjoy reading
through the advice you have given others on your Web site. I have two
crotons at work. I have moved to a new desk that has lots of bright light,
so the leaves are taking off. There is a lot of vigorous growth and the
leaves are five times as large as the existing leaves underneath the plant.
I'm happy with this, but the new leaves do not have the tricolor effect
that the leaves on the plant had when I purchased it. How do I get the
plants to go from green to the red/yellow/green hues it used to have?
(e-mail reference)
A: Try backing off
on the direct sunlight by about 50 percent. The different colors should
return after that. Crotons are tropical subcanopy plants that can get
by with some direct or mottled light, but when given a generous amount,
will tend to fade in color.
Q: Why are the cottonwood
trees in our city losing leaves and sometimes their branches? The leaves
are still green for the most part. This is happening all over our city
and no one seems to know why. (Valley City, N.D.)
A: A couple of maladies
can cause this to take place. I have a laundry list to select from,
which could be any or all causing the problem. The problem could be
happening because of the extended drought conditions. Cottonwoods and
hackberry trees often will drop leaves and branches as a means of conserving
water. It could be called “drought dormancy.” This dormancy
keeps the trees from dying during a stress period. Twig girdlers and
twig/branch pruners are two insects that will attack trees under stress.
Their egg-laying activity or larval feeding can cause twigs to drop.
Petiole galls and twig galls are caused by insects and their feeding
activity. The galls weaken the tissue surrounding the stems or twigs.
There might be a few more that I cannot think of at this time, but these
are the major causes of this problem.
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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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