|
October
21, 2004
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: Out of 40 dogwood
trees, only one small group is having problems. Dark spots began appearing
on the leaves within the last week. The leaves are now drying up and falling
off. The trees are about 4-years-old. They are watered from a well and
no pesticides have been used. (Dickinson, N.D.)
A: I don’t
know what to recommend. It appears to be a fungal leaf spot disease
of some sort. There is a plethora of problems with this species, so
anything and everything is possible. Send a sample to the NDSU plant
diagnostic lab for an accurate diagnosis and remedy.
Q: Creeping Jenny
is taking over our lawn. We are somewhat environmentally conscious and
have never sprayed our lawn with any type of weed killers. Is there a
safe, effective way to control this invasive weed? (e-mail reference)
A: The easiest control
is to purchase a rake with tines closer together than an average sand
rake. The tines are not flexible like a lawn rake. By raking the weed
with this close-tined rake, you actually pull it out quite easily and
you will be left with quite a mound of the stuff. You can compost it
as long as you don’t let it root in your compost pile. Otherwise
discard it. Repeated raking will control this weed nicely. Another option
is to discourage it from growing by altering the soil chemistry in your
lawn area. This is the last thing I’d recommend because it can
be a long-term control. Adding boron to the soil at a rate of 2 pounds
of borax (use regularly available Borax soap to supply the necessary
Boron) to 1,000 square feet of soil will increase the boron levels to
the point of toxicity to the creeping Jenny, but not the grass. If you
use the liquid Borax, use 20 ounces to the same 1,000 square feet. It
doesn’t matter whether you use one gallon of water to spread this
20 ounces across the 1,000 square feet or 100 gallons. The constant
amount is 20 ounces of liquid Borax soap spread across 1000 square feet
of ground. In both examples, this is a one-time application. Do not
repeat it every year. This treatment will not kill the creeping Jenny
right away like pouring boiling water on it will. It will start to weaken
the plant and the roots will have increasing trouble rooting and growing.
It starves the plant to death and the length of time it takes to die
could be several years (depending on how well you kept it fed and healthy
before). Combine the raking with the borax and you have a control that
is both effective and safe. If all of this is not to your liking, you
can try to solarize the plant to death. Spread clear plastic sheeting
over the area to be treated, seal the edges and attempt to cook it slowly,
assuming your creeping Jenny is growing in full sun. If this isn’t
the case, then the elimination of all light via thick black plastic
will do it. You need to keep it covered until just before the snow flies.
Q: We have many ant
hills in our yard. They are the small ants (much smaller than carpenter
ants). We have many oak trees and our soil is very sandy. The ants are
causing problems on newly seeded areas and are a pest when they get on
backyard beverages! We live on a lake, so I am looking for an organic
way to control them. All pesticides I read about are too toxic for the
lake, our children and our new puppy. (e-mail reference)
A: Any pesticide
will have some toxicity to non-target organisms. The question comes
down to the dose and longevity. Try a boric acid solution. Mix a cup
of water, 1/2 cup of sugar, 1 1/2 teaspoons of boric acid and shake
well. Fill small bottles with cotton balls and saturate the cotton with
the toxin. Poke small holes in half the lid so ants can get in. Turn
the bottles on their side in heavily infested areas. The ants will bring
the bait back to the nest and eventually kill off the colony. Some people
have claimed success with sprinkling boric acid around each ant nest.
If you have any
large ant nests, try the boiling water approach. Another idea is to
mix mint tea with Safer’s or Schultz’s insecticidal soap.
Follow the mixing directions on the bottle and then put the mix in a
spray bottle. It kills ants on contact and repels survivors.
Q: I think I overwater
my two spider plants. They were such beautiful plants, but now I have
one plant that may not make it and the other plant is all brown on the
bottom. Do you have any suggestions on what I can do to save the one stalk
that I have? I was thinking of watering it just once a week. Should I
put plant food in it? Also, my apartment is very hot. (e-mail reference)
A: Spider plants
are able to tolerate high temperatures, so don’t worry about that.
Water the plant as needed, but do not allow the container to stand in
water after irrigation. Hold off adding fertilizer until new growth
is evidenced.
Q: My lawn has large
patches of strawberries and clover. Broad-leaf weed treatments have not
been effective. I could use a vegetation killer and reseed, but what about
the strawberry-clover-grass combo areas? (e-mail reference)
A: I am willing
to bet that what you are calling strawberries is actually a weed that
looks like it. Potentilla bears yellow flowers while strawberries have
white flowers. Strawberry plants are very susceptible to broadleaf herbicides.
If you haven’t, give TRIMEC a try. It is a three-way compound
that is very effective in controlling just about any broadleaf. If that
fails, then the plants have built up resistance to the active ingredients
or it wasn’t properly applied. You would then have to resort to
a total herbicide such as Roundup.
Q: I have a number
of hollyhocks in my garden that have had their leaves turn a rust color.
The leaves eventually dry up and look terrible, but don’t fall off.
The stock of the plant has rust/brown, elongated, oval shaped marks on
it. What can be done to eliminate the problem? I don’t want it to
spread to my other flowers. (Fargo, N.D.)
A: Rust fungi are
host specific and need an alternate host to complete their life cycle.
However, they don’t carry over to hollyhock. This species of plant
has what is known as an autoecious rust because this type has only one
known infective stage and is not known to have an alternate host.
To control the problem,
cut the plants back to ground level, collect all the leaves and other
debris and destroy them. Avoid crowding the plants, water only in the
early part of the day and avoid splashing on the foliage. Early in the
season, apply a fungicide for protection. Chlorothalonil and Mancozeb
are two examples.
Q: I have a flowering
crab and an apple tree that are losing their leaves. The leaves turn yellow
and then fall off. Both trees blossomed last spring and have new growth.
I sprayed with a broad spectrum fungicide thinking it could be scab or
rust. (Tioga, N.D.)
A: It sounds like
a bad invasion of apple scab. Once the leaves are contaminated and showing
symptoms, there is nothing that can be done, but I doubt you will lose
the trees from this one event. Completely clean up under and around
the trees this fall. Next spring, spray the trees with lime sulfur.
When they bud, spray with Captan, Mancozeb, or Benomyl. Also spray after
every rain. Do not fall in love with a particular fungicide because
resistant strains may evolve if you do. Alternate between at least two
fungicides and introduce a new one the following year.
Q: I have a couple
of mature spruce trees in my yard. I think they are Norwegian spruce.
The bark became scaly on the outside and this week my seven-year-old grandson
began to peel the bark off of one tree. I stopped him and explained the
function of bark. Unfortunately, he later returned to the scene of the
crime and proceeded to peel quite a bit of bark from the tree. He did
not break the inside layer. Will this damage the tree? (e-mail reference)
A: Tar and feather
your grandson! I’m kidding because what he did won’t harm
the tree. I suggest telling your grandson that the tree is helping us
stay alive by providing air for us to breathe and that thanks to all
the trees in the world, he could be born and enjoy his parents, grandparents,
friends and pets. Even if the tree doesn’t complain, it makes
the tree sad to have its outer skin peeled off. An approach like that
may work better than telling him not to peel the bark.
Q: Can I root a crepe
myrtle tree from a stem or cutting? (e-mail reference)
A: Yes you can.
Take cuttings from the current season’s growth and dip it in a
rooting hormone powder. Stick the cuttings in a sand/peat mix (50/50)
and keep moist. The cuttings should root in four to five weeks or sooner.
Q: Some of my daffodils
are in a bed that has become shaded as the trees around it have grown.
I would like to move
them to an area with more sun. When is the best time to dig them up? Do
I have to do anything special to the bulbs before I replant them? (e-mail
reference)
A: Move them after
a good frost hits your area. Replant only healthy, firm bulbs and discard
the others.
Q: Over the past few
years the lower leaves of my tomato plants have turned yellow and fell
off. Eventually there was hardly any foliage and the plant produced very
few tomatoes. I tried adding powdered milk to each plant when I put them
in the ground. I thought this was working because they all looked good
and then I noticed that the yellowing returned. (e-mail reference)
A: Hearing about
using powdered milk on tomato plants is a first for me. Use Miracle-Gro
or something similar at planting time for tomato and other vegetable
plants. Avoid overhead watering; rotate the planting site, make sure
the soil is well drained and that the plants get full sunlight. Also,
try to select resistant cultivars.
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.
###
Source: Ron
Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
|
