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March
4, 2004
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: What causes oaks
to die when several feet of soil are packed around the roots and air is
pushed out? (E-mail reference)
A: That’s
a good question. Oaks are especially sensitive to soil fill over their
roots, with just inches, not feet of fill resulting in their death.
When the air is driven out of the root zone, anaerobic conditions then
exist and the free exchange of respiration gasses can’t be released.
The roots cannot pick up enough oxygen from the soil pores. In the absence
of this oxygen, the meristematic regions of the small roots are injured
because of inadequate aeration. When this occurs, alcohol, lactic acid
and other incompletely oxidized substances accumulate in the roots,
resulting in their eventual death. Basically, in the absence of oxygen,
the terminal electron transport system cannot operate, which then results
in less energy being produced, growth being reduced and finally death
due to the accumulation of toxic substances. It’s like the Great
Salt Lake in Utah; everything accumulates, nothing flows out. The result
is something that cannot support life as we know it (great for floating
things though). In nature, distribution of many species is restricted
by high oxygen requirements, which exclude them from flood plains or
areas where soil tends to be saturated. Those that are adapted to flooding
and can tolerate backfilling to a certain degree have a stem or root
system that interacts in some way to affect the gas exchange, or they
are simply tolerant of anaerobic respiration.
Q: After successfully
rooting some cuttings from my dieffenbachia (compacta), the parent and
some cuttings started to yellow all over, put out small and deformed leaves
and almost halted all growth. After trying everything, I discovered spider
mites everywhere. I rubbed each leaf, tapped the leaves to knock the mites
off and gently hosed everything down. I will spray with insecticides tomorrow
and repeat. Is the deformation permanent? Is higher humidity favorable?
How do I protect the rest of my house? For the winter, the whole "family"
is boxed up under a 16-hour florescent light, with the temperature set
at 80 degrees and 25 percent humidity. (E-mail reference)
A: I did mention
coffee in one of my responses to another insect control question. It
was in reference to using strong cheap coffee after it has cooled to
get rid of soft-bodied insects. The concentration of caffeine has a
detrimental effect on their nervous system, proving that anything can
be a poison if the dose is high enough! Your plant and offshoots sound
like they will survive, but the deformation will remain on those particular
leaves. To protect the rest of the house, mist the plants on a daily
basis especially the undersides of the leaves. Spidermites are as effectively
controlled with a spray of water as they are with insecticide/miticide
applications.
Q: I have recently
moved to a home with a neglected apple tree that is at least 12-years-old.
On one branch I noticed it was pealing almost like a snake shedding its
skin. Do you know what that could be? Do you think it's possible for me
to revive it? (E-mail reference)
A: Peeling bark
is sometimes a characteristic of older trees. It sounds like it has
been pruned very little over the years. I suggest tactful, focused pruning
this spring before new growth begins, with the idea that you want to
open the center of the canopy to allow for better air circulation and
sunlight penetration. If you don't know what you are doing, get somebody
else to do the pruning. Poor pruning has ruined many a good tree. No
more than 25 to 30 percent of the crown should be removed in any given
season.
Q: I recently read
a letter to you from a Jamestown resident with concerns about spotted
flies in his attic. I would greatly appreciate it if you could send me
the same information because these flies are a pain in the neck. Also,
do you have any suggestions on how to prevent them, or at least help control
them? (Jamestown, N.D.)
A: The flies enter
the house in the fall of the year as the temperatures begin to drop
close to freezing. If the temperature doesn’t drop too low where
they have settled in, they can go into a dormant or resting stage and
become active again when the temperature goes up. Or, they can lay eggs
and when the temperature goes up sufficiently, the eggs hatch and eventually
morph into pesky flies. To correct this problem for next year, go over
the exterior of the house and seal up the smallest openings with caulking.
To take care of the problem for now, the sticky strips that hang from
ceilings or rafters will do an excellent job without using pesticides.
Also, the botanical pesticide, pyrethrum, is a good knockdown product
to control flies. It can be found anywhere that garden or houseplant
products are sold.
Q: I've had my jade
plant for years. It sits in a nice sunny window and I water it every week
to 10 days. For over a year it has had some kind of pest on the leaves
that makes the whole area under the plant (table and floor) very sticky.
Recently, the problem has gotten worse and it now seems to be harming
the plant. I'm getting some leaf drop. Is it aphids? What should I do?
(E-mail reference)
A: It’s most
likely spider mites doing the damage. Spider mites are almost invisible
to the naked eye, while aphids, which can cause the same problem, are
easily visible. Check under each leaf to see if there is any stippling
(yellow dots) on them. If there is, that’s where the mite has
inserted its stylet and would be the cause of your problem. If you see
small white cotton looking pieces at the juncture of the leaf petiole
and stem, then it is an invasion of cottony cushion scale.
If it is the spider mite that is causing the problem, move the plant
to your bathtub and spray the top and underside of the leaves. That
will disrupt them as good or better than many insecticides. If it is
the cottony cushion scale, then take a cotton ball and soak it in rubbing
alcohol and wipe the scale off the leaves completely. Look along the
stem as well. If you see little brown bumps, it likely is an invasion
of San Jose scale. If that is the case, you are probably better off
dumping the plant, as control measures at this point are simply too
difficult to undertake.
Q: I have several
hackberry trees growing on my property, which consists of a 100 foot by
three mile section of abandoned railroad.The railroad was closed in early
the 60s and has quite a variety of good-size trees growing on it. It seems
the hackberry trees are beginning to take over on some parts of the property.
There are several small saplings coming up. Should I cut them down and
replace them with another species of tree? What is hackberry wood used
for? (E-mail reference)
A: I don't know
why you would want to cut down hackberry trees. To me they are attractive,
tough, disease-free (the witch's broom and nipple gall they get are
just cosmetic) plants that most people would be happy to have coming
up as volunteers on their property. The wood of the hackberry tree is
a tough, twisted wood, with excellent resistance to breakage. Good quality
wood is used for furniture, millwork and some athletic equipment. Lower
grade material is used for crating. Hackberry trees are one of the most
eco-friendly trees in North America. The fruits are relished by wildlife
because of their raisin/plum flavor. The branching system is such that
they are inviting to nesting birds and even those with decay hold up
well enough for owls and squirrels to move into. They also attract butterflies
with their nectar-rich foliage. The seedlings coming up are from the
consumed fruit of visiting birds. Think twice before cutting these trees
down. They are good for the ecosystem, as well as perhaps softening
what has to be an eyesore, an old, unused railroad track.
Q: I have a spider
plant that is huge. I am thinking about separating it into two pots. What
is the best way to do this? (E-mail reference)
A: Knock it out
of the pot. With a sharp knife or a pair of pruners, cut it in half
or quarters depending on the size of the crown, and replant.
Q: Some of the blue
spruce I planted last fall are getting reddish brown needles. The problem
is on the south and southwest sides of the tree. I purchased some Wilt-Pruf
to spray on them. Is it advantageous to spray them now? What temperature
is the minimum at which you can apply Wilt-Pruf? Will mulching at this
time of the year do any good? (E-mail reference)
A: Spraying Wilt-Pruf
at this time of year will help as long as the air temperature during
the day is in the upper 30s or lower 40s. Mulching will not do any good
at this time of year. Even though we have had a very cold winter, with
lots of snow, we have also had some very high light intensity days with
light reflection coming from the snow. This raises the internal temperature
of the needles on the south and southwest side of the evergreens to
the point where they begin losing moisture. Because the needles are
still frozen, the moisture can’t be replaced, resulting in discolored
needles. Wilt-Pruf now will prevent that from happening further.
Q: I have been collecting
cuttings and plants for years but I have a few questions. When growing
an aloe, do you keep it root-bound for flowers and better growth or should
you remove the pupsand and start fresh every few years? I have a few specimens
from California that do extremely well root-bound, but I don’t want
them to die. What are the best growing conditions for epiphyllum? I have
cuttings that have been growing for two years but are starting to grow
thin leaves, not the broad leaves like the parent plant. I have a starfish
plant (Stapelia gigantea) that I managed to grow from a cutting, and it
recently bloomed. Do you take care of it the same as a succulent? I found
out it is part of the milkweed family so I’m very confused about
how to take care of it. All of these plants are indoor and are located
on the east side of the house near a window. (Minot, N.D.)
A: You have obviously
developed cultural practices that allow you to maintain the aloe in
a pot-bound fashion. Aloe and other succulents should be repotted only
when necessary and then only into the next nominally larger container.
Be careful to adjust your cultural practices, especially watering, to
reflect this move. Repotting, in most instances, is done close to spring.
Epiphyllous is closely related to Christmas cacti. It will respond to
short day treatments to bloom. The undersized leaves could be caused
by insufficient light at this stage of development. Try supplementing
with additional plant lights to see if that doesn't increase their size.
I hope you got the odorless species of Stapella gigantea or else I hope
you have lost your sense of smell! It is a succulent and should be watered
minimally in winter, kept in bright, indirect light, summered outdoors
and watered moderately the rest of the year. Allow the potting soil
to go dry between waterings.
Q: Our ailing blue
spruce was planted in 1957. It is 15 feet from our house, 15 feet from
the corner of the neighbor's house and about 9 feet from the neighbor's
downspout. It is alongside our concrete driveway. The problem is massive
needle drop with dead or dying branches. Some years I have sprayed with
Malathion but it is so tall now that such spraying seems pointless. What
shall we do to save it? Is it doomed? (Moorhead, Minn.)
A: Call James Danielson
at (701) 729-7208, or Kelly Melquist at (701) 729-6899. Both are International
Society of Arboriculture certified arborists. They can give you an accurate
diagnosis and course of action. It may turn out that the tree has lived
beyond its ecological and genetic limits based on the location you describe.
When spruce trees get to be that size and age in suburban environments,
they become very susceptible to diseases and become difficult to sustain.
Trees at this stage commonly suffer from cytospora canker or rhizosphaera
needle cast. Hope this is the information you are looking for.
Do you have a gardening
or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension
Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu.
Note to e-mail correspondents: please identify your location (city and
state) for most accurate recommendations.
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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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