Horticulture In North Dakota:
Seasonal Tidbits and Tips
Extension Report No. 21, October 1999
Ronald C. Smith, Extension Horticulturist and Turfgrass Specialist
Causes of Winter Injury to Landscape Plants
Most landscape plants grown in North Dakota are hardy enough to withstand all but the
lowest temperatures on record. There are basically two causes of winter death to what are
considered hardy landscape plants:
- Desiccation - this frequently happens to evergreens when the sunlight intensity
is high, causing the plant tissue to become physiologically active. Water is lost at this
time and cannot be replaced because of the frozen soil water.
- Freeze-thaw cycles - common on herbaceous plantings that were not given mulch
protection before winter. It occurs during our typical February/March thaws and refreezes.
The crown of the plant is heaved, causing roots to be exposed to the fluctuations of air
temperature. The root system has a lower tolerance to temperature extremes and may be
killed by a lethal low temperature.
Other causes for physical damage to woody plants are wet, heavy snows, or freezing
rains and sleet. Expect this to show up on soft-wooded trees like silver maples. The
weight borne by the branches causes rip and tear breaks to take place. Immediate clean-up
of broken branches by cutting back to a crotch or healthy branch is the best action.
Winter desiccation can be minimized by planting sensitive species in sheltered
locations, providing companion plantings that are more resistant to winter desiccation, or
by screening with burlap, evergreen boughs, or discarded Christmas trees. All of these
measures will slow the loss of water from the valued plant material.
Spraying commercially available anti-desiccants on the plant foliage in late fall and
again in late winter will provide adequate protection. The clear, protective film slows
water loss from plant tissue exposed to the elements.
The common term "sunscald" is a poor one, as it leads to misunderstanding by
many beginning gardeners. This is desiccation that is confined to specific locations on
newly planted, thin-barked trees. Wrapping with paper, burlap, or PVC tubing is needed
before the onset of winter, to be removed the following spring once the frost is out of
the soil.
Checking the herbaceous plantings as winter grinds to a close to see if re-setting or
re-mulching is needed, will cut down on loss. Covering the plants prone (new transplants
mostly) to heaving with a light organic mulch once the soil has initially frozen will help
to minimize this type of loss.
Rabbit and Mice Damage
Prolonged snow cover throughout North Dakota can cause rabbits to damage trees and
shrubs through the winter months. The severity of damage can vary from slight to total
girdling of the stems or trunk. In some cases, as with single-trunk trees, a complete
girdle almost always results in the death of the tree. With shrubs such as raspberries,
the season's crop is lost, but the plants are not. Cut the girdled branches back to ground
level, and new growth will surge forth in the spring.
Where a tree has been completely girdled, and the plant has high value to the owner,
bridge grafting can be attempted, as explained in publication NCR 274, Home Propagation
Techniques. Generally if the tree is just one or two seasons old, it is better to simply
replace the plant entirely than to attempt a patch-up job.
Take preventative measures before winter arrives with proper protection.
Mice or voles will also cause heavy damage during extensive snow cover, with the
evidence not showing until snowmelt the following spring. The treatment is the same, as is
the prevention. It has been found that moth balls or crystals will help to repel these
rodents if they are spread at the base of vulnerable plants prior to freeze-up or snow
cover. Since these materials give off obnoxious fumes from either naphthalene or camphor,
handle with care, and keep away from children and pets.
Deicing salts are used throughout our region in an attempt to control ice build up on
paved surfaces. The most economical material for cities and counties to use is sodium
chloride, which is mixed with sand. As the spray drifts onto plant tissue, it can cause an
acceleration of the dehydration of plant tissue, sometimes to the point of death. Screens
of burlap will help to protect the non-tolerant species - evergreens, both broad-leaved
and needle. On turf areas, a good wash-off with a garden hose spray will keep the grass
from suffering salt stress. Subsequent rains will leach the salts from the soil.
The Proper Time to Prune
A major portion of the landscape can be pruned during the late winter or early spring
months. Doing it
on a mild winter's day will often help to chase the blahs and blues of this long season,
and get the juices flowing for spring planting. Besides, it is great exercise, waking up
(or rediscovering) working muscles!
Grapes: Anytime in March or early April. Refer to circular on proper
technique.
Fruit Trees: Anytime from March to early April.
Shrubs: Spring flowering shrubs should be pruned right after
flowering, if there is desire to appreciate the flowers that spring. Otherwise, prune them
while they are dormant. Avoid pruning in late summer, as this may result in a flush of
growth which would not harden off in time to prevent winter injury.
Evergreens: Arborvitaes, yews (eastern part of the state) and junipers
are best pruned before new growth begins in early spring (April or May). A follow-up
pruning can be carried out in June or early July to shape up the new growth.
Shade and Ornamental Trees: Like fruit trees, the best time for most
is in late winter or early spring while still dormant. Maple, elm, black walnut, and birch
bleed heavily when pruned in the spring. This doesn't cause a problem for the tree as much
as it does for the pruner who worries about the excess sap flow. Better to wait until
these trees have completely leafed later in the spring before pruning.
Starting Garden Transplants
Late winter is the time most nervous gardeners – both beginners and experienced
– begin or at least contemplate growing transplants for their gardens. Many fall into
the trap of starting too early, to only end up with weak, spindly seedlings from too much
heat and too little light. Seedlings like this should not be moved into the garden,
but disposed of, and begin again with a fresh planting.
Before sowing seeds for garden transplants, make sure of a constant source of light,
controlled heat (bottom is best) source, and the ability to control watering. The light
source is most important, and can be easily met with cool and warm white fluorescent lamps
or "grow lamps." Seedlings develop best under a 12-hour lighting regime, with
night temperatures 10 degrees cooler than day – between 65 and 75 degrees Fahrenheit
for daytime.
Most seed packets and seed catalogs provide good information on germinating seeds and
growing them on to transplants. Some require light (like petunias) and should not be
covered; the ones that require darkness (like Calendula) should be covered enough to
exclude light. The seeds can be germinated in any container that is clean, but the soil or
medium should be well-drained, pasteurized material, from a commercial source, not
back-yard garden soil.
Back up from the last expected killing frost date anywhere from four to 10 weeks to
arrive at the date of sowing. For example, Calendula would be sown around the 15th to 20th
of April; petunias, needing 10 to 12 weeks to develop after germinating, would be sown
around the end of February or first part of March.
Most home gardeners are better off making bedding plant purchases at a local retailer
than attempting to grow their own seedlings. People always start with good intentions but
are unable to maintain the commitment adequately to produce decent transplants for their
garden.
A Few Words About Fruit Flies
Many calls come during the winter months about small bugs flying around in the kitchen.
When they can be captured and not crushed with a good smack, they inevitably turn out to
be the red-eyed characters we studied in entomology classes known as fruit flies. While
their presence is an annoyance, they cause no harm.
These little pests originate from fresh fruit sources, where decay and fermentation is
taking place. Other than over-ripe bananas or apples sitting out in a basket too long,
other most likely spots are the above-water line in a slow-moving drain or dirty garbage
containers. Location of the breeding area is often difficult and requires a good
detective's mind.
Techniques to eliminate the breeding sites vary – a stiff brush or stick can be
used to scrub the slime from inside the drain pipe; a chlorine bleach soak and scrub will
eliminate them from garbage containers. Anywhere slimy water collects, a potential problem
exists.
In most instances, the fly population is just a temporary annoyance, with the flies
disappearing on their own without a source ever being determined.
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Early Spring's Frantic Activities
Banding and Horticultural Oils
Cankerworms are plant defoliators that emerge in the spring shortly after the trees
leaf out. They are commonly found feeding on the foliage of fruit and elm trees. These
larvae are among the most easily recognized, being commonly called "inch worms"
by kids who discover them, and as loopers or measuring worms by others. The larvae are a
striped light green brown or black, with only two pairs of abdominal prolegs present (as
compared to three pairs of prolegs on the fall larvae, which will be hatching and feeding
at the same time). The adult female moths (wingless) hatch from the soil around the base
of the trees and begin crawling up the trunk in April to lay eggs.
Because of the wingless, crawling characteristic of the female moth, she is vulnerable
to being trapped with a sticky material known as "Tanglefoot." These bands
should be in place before April 1 to maximize effectiveness in trapping. The bands must be
at least 2 inches wide to be effective.
The cool, wet springs of 1992 - 1994 saw very little cankerworm activity, due to the
delay in hatching, predatory action, and parasites destroying the egg masses.
Should a tree or trees become heavily infested with cankerworm larvae, a spray program
with Dipel or BT will very quickly kill them from this bacteria and not affect other
active predators working in the area.
Another arsenal to depend on in controlling scale, aphids, and mites, is horticultural
oil – often mistakenly sold as "Dormant Oil." Through improvements in
refining, these so-called dormant oils can now be safely used on most woody plant species
to control many insects.
These oils work by three modes of action: asphyxiation – the blocking of oxygen
diffusion to eggs or scale adults; interaction with fatty acids within the insect cells
that lead to disruption of cellular metabolism and eventual death; finally, by disrupting
the normal feeding patterns of aphids and leafhoppers.
The only possible disadvantage to using horticultural oils is the slight risk of
phytotoxicity. If they are used between the temperatures of 40 and 95 degrees Fahrenheit
and when the foliage is dry, along with avoiding use when bud elongation is taking place,
no toxicity to the plants will be experienced. Some plants are sensitive and should never
have horticultural oils sprayed on them. These would include: sugar maples, beech,
hickory, and Douglas fir. With Colorado blue spruce, the oil sprays are not
toxic, but will cause them to lose their blue color.
Disease Management – Late Winter or Early Spring
The purpose behind disease management at this time of year is to reduce the amount of
inoculum that has overwintered, thus reducing the potential for problems during the
current year.
Apple
Fire blight – prune out all blighted twigs and branches. Make cuts in dry
weather, 8 or more inches below the visible canker. On trees with fire blight the previous
season, a spray of Bordeaux mixture or copper sulfate will cut down on the survival of the
remaining bacteria. Sprays of streptomycin or terramycin during bloom are advisable on
susceptible cultivars.
Apple Scab – Select scab resistant cultivars; on scab susceptible plants,
spray before bloom, during bloom, and after at set intervals. Start with lime-sulfur when
the tree is dormant, then move into Captan and Benomyl when the tree begins
leafing out, and beyond.
Cedar-Apple Rust – This is an alternate host fungus, consequently the
removal of junipers (commonly and incorrectly called cedars), or a least the close
monitoring of them to remove the fruiting bodies of the fungus to interrupt the life
cycle. No fungicides are labeled for cedar-apple rust control.
Sooty-Blotch & Fly Speck – These are very descriptive terms for topical
diseases that show up on fruit during cool, wet growing seasons, (ie. 1992–94). While
the aesthetics of the fruit are reduced, the eating quality is not. Captan or Orthocide
can be used as a preventative, starting in early July, and ending 30 days before fruit
harvest.
Cherry and Plum
Black Knot – Survey and prune out all diseased branches while still dormant
in late winter or early spring. The use of lime sulfur spray at this time will also help
in the control of the disease.
Brown Rot – Captan, Benomyl, and sulfur can all be used
according to label instructions for control. While good sanitation is a good measure for
all disease control, it is especially so for this one. Be sure to rake up and destroy all
infected fruit.
Plum Pockets – Lime sulfur is a good one to use for the control of
this disease when the trees are dormant.
Raspberry
Anthracnose – Again, lime sulfur or Orthorix just before bud
break is effective.
Strawberries
Gray Mold and Leaf Spot – Controlled by Benomyl and Captan as
new growth begins, and again when the plants begin flowering.
Crabgrass and Other Annual Weed Control in Lawns
Let's first identify why spring treatments of turf weed problems fail:
- Misidentification of the weed: Annual weeds in North Dakota include,
but are not limited to; crabgrass, annual bluegrass, barnyard grass, wild buckwheat,
shepherd's purse, the foxtails, and lambsquarters. Often these weeds are visibly seen, and
a preemergent is applied to no avail. Perennial weeds (dandelion and broadleaf plantain)
are difficult to control in the spring because of the surge growth taking place.
- Waiting too long: Weeds are most vulnerable when they are beginning
active growth, and that's precisely when the pre-emergent herbicides work. As the weed
seeds begin to germinate, the herbicide is effective; once established, the effectiveness
is reduced or eliminated, depending on the herbicide.
- Failing to repeat applications: Seed germination is a progressive
phenomenon, not a sprint out of the starting block. A repeat application two weeks later
will provide more satisfactory control than any single one will. Crabgrass seed germinates
from May until August, thus assuring survival as a pest.
- Impatience: This relates to timing. Mature, toughened plants getting
through the mid-summer heat will not respond to herbicides nearly as well as
well-nourished, lushly growing weeds. Get the weeds growing well, then zap them.
Most annual weeds can be controlled when herbicide applications are made at the
seedling stage. When the weed is allowed to continue development, a chemical messenger
formed in the plant tells it to go from a vegetative to a reproductive stage. Herbicide
control is less effective at this stage. When the plant has completed its life cycle, and
the seeds are produced, the cycle is ready to be repeated, and chemical control is no
longer effective on the senescing plants. Figure on these hypothetical numbers:
Germination to seedling stage = 100% control; vegetative stage = 75% control;
flowering/reproductive stage = 30% to 40% control.
Although weeds cannot be eliminated from life, most homeowners create problems for
themselves by poor cultural practices. Mowing too short, poor watering cycles and
duration, no fertilization or poor timing of fertilizer applications, and selecting the
wrong grass for a particular site. Mow between 2.5" and 3.0"; water deeply
(4" to 6" soil depth) two to three times/week; if a single treatment of
fertilizer is to be applied, make it in late August or early September, if two, make it in
the spring in May after the grass has begun active growth; Kentucky
bluegrass/perennial ryegrass/fine leaf fescues are the best general combination to grow
across the state. Salty, dry sites need fairway crested wheatgrass and creeping alkali
grass; shaded, damp areas need fine fescue and rough bluegrass combinations.
Chemical Control of Annual Weeds in Lawns
Pendimethalin - (Lesco Pre-M, Scott's, Weedgrass Control, Halts Crabgrass
Preventer and others). One of the most visible, economical, and effective products on the
market.
Dacthal - Provides excellent control; often found in combination herbicides
Tupersan - This one allows the overseeding of desirable grass species while
providing excellent control of grassy weeds. Not as readily available, and more expensive
than the others. Popular with landscapers in the business of installing lawns.
Acclaim - Excellent postemergent control of grassy weeds, low potential for
turfgrass injury.
Spring Lawn Care for Procrastinators
With all the other spring chores needing to be done, lawn care sometimes takes a back
seat in priority. In some ways this is good, as initiating lawn care too early is often
the source of problems later in the season. This is especially true if the lawn needs
compaction relief or dethatching. While the two operations to correct these problems
– aeration and power-raking – are best done in the fall, if these problems are
serious enough to prevent turfgrass cultural practices from being effective, then carrying
out either or both operations in the spring – once the grass has begun active growth,
usually early May – is an acceptable time to address these concerns.
Although thatch sounds like a public enemy to be eliminated, it only becomes one when
it accumulates
in excess – beyond 1/2" in thickness. Thick thatch may be soft and springy to
walk upon, but it predisposes the lawn to poor water, fertilizer and pesticide
utilization, makes it vulnerable to drought, and the roots do not penetrate deeply (if at
all!) into the soil below. Other problems, like diseases and scalping when mowing, will
eventually prompt the homeowner to do something about it.
Dethatching should be done when the soil is moist with a machine that can be rented
locally for that purpose. The lawn mower attachments that tout dethatching capabilities
are useless and destructive to both the lawn and mower. Usually fertilizer, and sometimes
crabgrass control or reseeding is carried out after the dethatching is completed.
Thatch or not, most lawns would benefit from an annual aeration. This is especially
true where the turf areas are growing in clay soils. The pulled cores can remain to
gradually disintegrate, be raked out, or broken up with a power rake (vertical mower).
Because the root zone then has an abundance of air, the grass plants will be able to more
effectively take up water and nutrients. The result: a fertilization effect.
Transplanting Trees and Shrubs Within the Landscape
When the need arises, and the plant material is not too large for the homeowner to
handle, transplanting trees and shrubs to better locations for aesthetics or the
survivability can be carried out. The best time to move plants is when they are dormant
– early spring before leafout, or in the fall after leaf drop.
Branches are tied up to cut down on interference and possible damage while digging and
moving. The soil should be moist when the digging commences, and as much soil should be
moved with the roots as can be comfortably handled.
Start by digging a trench around the tree with a spade, coming out about 10" to
12" for each inch of caliper on the stem about 4 feet up. Once the trench is
complete, undercut the roots with the spade, lay a piece of burlap on one side of the
trench with about half of it rolled to tuck under the rootball. Gently rock the rootball
back, and slide the burlap under, roll the ball back in the opposite direction, and pull
the burlap up around the ball. Secure the burlap tightly with a twine or rope, then lift
gently by the ball and move to the new site. Try to avoid breaking the ball of soil during
this whole process. If it should break, don't panic! Chances are the transplant will still
survive if the task is completed quickly.
Set the transplant at the same depth in the new location and water in completely. Carry
on some top pruning – no more than 1/3 of the branching system – to balance out
with the reduced root system. Homeowners often attempt to move plant material that is too
large for them to successfully handle. Anything above 3 inches in caliper should be left
to a professional.
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Extension Report No. 21, October 1999
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