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May
13, 2004
Spring Frost
Damage to Crops Could Be a Problem
Temperatures at freezing
or below for an extended period of time could damage some crops, according
to Duane Berglund, North Dakota State University Extension agronomist.
“Temperatures below 32 degrees will cause water in plant cells to
freeze. How different crop species react to freezing temperatures depends
on where growth is taking place, where the growing points are and if cells
have built in systems to prevent ice crystal formation.”
Seedlings hardened by continuous low night and day temperatures are more
resistant than seedlings hardened by alternating high and low temperatures.
The recent cool nights may have helped in the hardening process. Also,
the rain, which brought wet soils in the eastern part of the state and
snow cover in some northern areas, will help reduce or temper the threat
of a killing frost.
“There are considerable variety differences in all crops but little,
if any, research has been done concerning frost tolerances on the varieties
producers are currently growing,” Berglund says.
CORN-
Corn plants less than six inches tall (V-5) will recover from frost because
the growing point is still below the soil surface and usually not damaged.
Lethal cold temperatures (28 F or less) can penetrate the upper inch or
two of soil, especially if the soil is dry, and kill plant tissue including
coleoptiles and growing points. “Hopefully, the recent rains have
wet the soils adequately enough to provide a buffering effect to the cold,”
Berglund says. “Non-lethal injury by cold temperatures may cause
deformed elongation of the mesocotyl or physical damage to the coleoptile
in non-emerged seedlings, resulting in the “cork-screw” symptom
and subsequent leafing out underground.”
Historically very few corn fields have been destroyed by spring freezes
but very limited research has been done on this subject. Damage to seedlings
could be a complete kill, injury so severe that the resulting seedling
is weakened to the point where it will never develop a normal reproductive
system or plant damage is evident, but seedlings remain vigorous and complete
recovery can be expected.
Environmental conditions before or immediately after low temperatures
greatly influence the extent of the damage. If the temperature drop is
gradual, plants are in better condition to resist injury and can stand
surprisingly low temperatures. Slowly rising temperatures after a frost
and satisfactory soil moisture conditions are desirable to aid recovery.
Drought, wind and high evaporation are likely to aggravate the frost injury
and decrease the chances of recovery.
SMALL GRAINS-
Cereal grains will lose leaf tissue that freezes. New growth will follow
at the growing point before jointing is protected below ground. In some
cases, the eventual maturity date may be delayed. “In some areas
this has already occurred,” Berglund says. “New leaves have
emerged and the crop is growing. However, several frosts and destroyed
leaf tissue can and will greatly weaken the growing cereal grains and
may result in yield reductions.” Small grains are among the most
frost tolerant of crops. From emergence to just before jointing, they
can easily stand temperatures of 25 degrees or even colder if they harden
off. After the 6-leaf stage and at jointing, the growing point moves above
the soil line and the cereal crop becomes more susceptible to freezing
temperatures.
Broad leaf crops that
have the growing point at the top of the plant are more susceptible to
frost damage than grass species. Soybeans, for example, are quite sensitive
to frost. Dicotyledonous plants such as sugar beet, sunflower, soybean,
dry bean and flax are more easily killed by frost than are small grains.
SOYBEANS-
Soybeans are easily damaged by frost in the 28 to 32 degree range. Temperatures
of 28 degrees for any extended period of time can completely kill soybean
plants (buds, stems and leaves).
During the early seedling stage (VE to VC), soybeans have some tolerance
to temperatures of 29-30 degrees for short periods of time. If the seedlings
have been somewhat hardened off by cool temperatures for several days,
then temperatures as cool as 28 degrees can be tolerated. Once true leaves
emerge (V1 and V2), soybeans become more susceptible to freezing temperatures
below 32 degrees for any extended period of time. Soybeans in the unifoliolate
leaf stage are slightly more frost tolerant than soybeans in the first
or second trifoliolate stages.
SUNFLOWER-
Sunflower in the cotyledon stage can withstand temperatures in the 25-26
F degree range for short periods if they are just emerging from the soil.
Sunflower in the 2-, 4- and 6- leaf stage become more sensitive with each
development stage and terminal bud damage can occur. “It’s
known that if sunflower is in the 2-leaf or V2 stage then 26-27 F degrees
is the lower limit, Berglund says. “For the 4- and 6-leaf stages,
28-29 degrees is the lower limit. Also, the tolerance can be influenced
by the hardening off process. That is, if it is cool or cold for several
days with 33-34 F degree nights, the seedlings can become somewhat accustomed
to the lower temperatures and perhaps a little more tolerant. It’s
going from warm to extreme freezing temperatures all at once that is the
most injurious. Wet soils and some dew also help in the reduction of freeze
damage.
FLAX-
Flax is quite susceptible to frost damage if it is just emerging. It can,
in some cases, tolerate temperatures around 27 F degrees early on. Seedlings
that have passed the 2-leaf stage and are hardened off by exposure, can
withstand temperatures down to 18 F degrees, according to literature from
Canada. It depends somewhat on growing conditions a few days prior to
a hard frost. Check if the stem is turning black. Flax exposed to the
lower 20 degree temperatures should be fine if hardened off.
ALFALFA-
Alfalfa will be damaged by temperatures in the mid to low 20s. Alfalfa
grows from the tip of the stem. If frost damage occurs, the top will bend
over and growth will cease. Plan to take the first harvest early, as soon
as the field dries enough for good equipment performance, Berglund advises.
OTHER CROPS-
Temperatures of 32 degrees F or below will kill buckwheat and drybeans,
while canola and crambe will tolerate temperatures in the low 20s. Crops
such as field peas or lentils have good frost tolerance since growing
points remain below ground in the seedling stages.
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Source:
Duane R. Berglund, (701) 231-8135, duane.berglund@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
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