NDSU Crop and Pest Report

Plant Science

ISSUE 2   May 13, 2004


Dry and cold soil conditions result in poor seedbeds which brings with it concern for erratic crop emergence and poor plant stand establishment. Some crops such as small grains, canola, sunflower and soybean can compensate for low plant populations.

Crop will compensate for stand reduction through tillering, branching or increased head or kernel size. Listed below is the minimum stand of several crops to avoid major yield reductions when making decisions on tearing up the field and replanting. Remember that a replant decision costs dollars and extra time. The later replant also may put the development of the crop into a more stressful period of stress such as a high temperature, drought or risks of frost.



Minimum Stand

% of Normal Stand

Small Grains

8-10 plants/sq. ft.



12-15 plants/sq. ft.



2-2.5 plants/sq. ft.


Canola, Mustard

3-4 plants/sq. ft.



11-13,000 plants/A



40-75,000 plants/A


Field peas

3-5/sq. ft.


Dry Beans

45-60,000 plants/A
28-40,000 plants/A


Even stands below 12 plants per square foot of barley and oats have yielded near normal because they typically tiller more than spring wheat which typically tillers more than durum. Refer to NDSU Extension Circular A-934, "Replanting after Early Season Crop Injury" for further information. Also available on the web at:




Temperatures are expected to drop below freezing in areas of North Dakota this week. What type of damage will be result with some of our crops now just emerging and in a vulnerable stage and subject to frost damage? Temperatures below 32 degrees F will cause water in plant cells to freeze and resultant ice crystals will kill cells by damaging cell membrane systems. How different crop species react to freezing temperatures depends on where growth is taking place, where 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 day and night temperatures. The cool nights we have had recently may have helped in the hardening process.

There are considerable variety differences in all crops and no research has been done on the varieties we are currently growing.


Corn plants less than 6 inches tall (V5 or less) will recover from frost because the growing point is still below the soil surface and usually not damaged. Lethal cold temperature is a concern since a corn plantís growing point region is relatively protected from the effects of simple frost while it remains below the soil surface. Lethal cold temperatures (28 F or less) can penetrate the upper inch or two of soil, especially dry surface soils, and kill plant tissue directly, including coleoptiles and growing points. 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 proverbial "cork-screw" symptom and subsequent leafing out underground.

Historically very few corn fields have been destroyed by spring freezes. Very limited research has been done on this subject. Damage to seedlings could be (1) complete killing (2) injury so severe threat the resulting seedling is weakened to the point where it will never develop normal reproductive systems, (3) injury evident but seedlings remain vigorous and complete recovery can be expected.

Environmental conditions before or immediately after a low temperature greatly influence the extent of freezing injury. If the temperature drop is gradual, plants are in better condition to resist injury and can stand surprisingly low temperatures. Similarly, slowing 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 lessen the chances of recovery.

Small Grains:

Our 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 and 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 reduction.

Broad leaf crops that have their growing point at the top of the plant are more susceptible to frost damage than our 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 are easily damaged by frost in the 28 to 32 F range. Temperatures of 28 F for any extended period of time can completely kill soybean plants (stems and leaves).

During the early seedling stage (VE to VC), soybeans have some tolerance to temperatures of 29-30 F 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 F can be tolerated. Once true leaves emerge (V1 and V2) soybeans become more susceptible to freezing temperatures below 32 F for any extended period of time. Unifoliolate leaf stage is slightly more frost tolerant than first or second trifoliolate stages.


Sunflower in the cotyledon stages can withstand temperatures in the 25-26 F range for short periods if they are just emerging from the soil. Sunflower in the 2, 4 and 6 leaf stages become more sensitive with each development stage and terminal bud damage can occur. Itís known that if sunflower is in the 2-leaf or V2 stage then 26-27 F would be the lower limit. For the 4 and 6 leaf stages the 28-29 F 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 such as 33-34 F at nights and the seedlings become somewhat accustomed to the lower temps, then perhaps a little better tolerance to lower temperatures. Itís going from warm temps to extreme freezing temperatures all at once that are the most injurious. Wet soils and some dew also help in reduction of freeze injury. Cold and dry conditions help add more to seedling injury.


Flax is quite susceptible when it is first emerging. It can, in come cases, tolerate temperatures of 27 F early on. After the seedlings have passed the two-leaf stage and are hardened off by exposure, can withstand lower temperatures down to 18 F according to literature in Canada. Depends some on growing conditions the previous couple of days before a hard frost. Check to see if stem is turning black. Therefore, after 2-leaf stage and hardened off it can stand temps in low 20's and recovery is very promising.


Alfalfa will be damaged by temperatures in the mid to low 20's. Growth of alfalfa is from the tip of the stem. With frost damage the top will bend over and growth of the tip will cease. Plan to take the first harvest as soon as field dries up enough for good equipment performance.

Other crops:

Temperatures on 32 degrees F and below will kill buckwheat or drybeans, while canola and crambe will tolerate temperatures in the low 20's. Crops such as field peas or lentils have good frost tolerance since growing points remain below ground in the seedling stages.

Duane Berglund
NDSU Extension Agronomist



About three-fourths of the total anticipated corn acreage in North Dakota had been planted by the most recent crop report (May 9th). Certainly by now the vast majority of the corn is in the ground. Provided there is sufficient moisture in the soil to enable germination, we can predict fairly accurately the emergence of corn based on the number of growing degree days since planting. In North Dakota, corn requires between 120-125 corn GDDs (corn growing degree days use a base temperature of 50 degrees F) to emerge. Table 1 lists the average date of emergence of corn, based on long term weather data, for selected locations in North Dakota and the GDD accumulations for 2002-2004 for these locations.

Table 1. Average date of corn emergence for selected locations in North Dakota using long-term weather data1 and GDD accumulations for these locations for 2002-2004 for the first 10 days of May.



Average date of corn emergence1

GDD accumulations
1 May to 10 May






May 15
May 20
May 18
May 17
May 13
May 15




1-Based on historical weather data available at NDAWN assuming a 1 May planting date and 120 GDDs needed for emergence. The years of available data for a given site were typically 10, but varied from site to site.

Even with the cooler weather that is predicted to move into the state for the next few days, corn that was planted on or before 1 May should be emerging by the end of this week in all but the northeastern part of the state. GDD accumulations are well ahead of those recorded in 2002 and 2003. Corn emergence will be more or less in line with the long term average date of emergence, but much earlier than in 2002 and 2003.

If you wish to monitor GDDs for your farm during the growing season, go to the NDAWN website  at http://ndawn.ndsu.nodak.edu/application/corn-degree-days-form.html, select the weather station nearest your farm and enter your planting date in the form where requested. GDDs are also useful in predicting corn growth stages. Generally early in the growth of the corn plant, 85 GDDs are required for the appearance of each new leaf.



In the past couple of days temperatures have dipped below freezing in many regions of the state. How damaging were these cold temperatures on the emerged small grains? Freezing temperature damage to small grains is dependent on the stage of the crop, the actual sub-freezing temperature reached and duration of the low temperature, and environmental conditions that existed before the frost occurred.

Small grains are among the most frost tolerant of crops and from emergence to jointing, small grains can easily withstand temperatures of 25 F. After jointing, the growing point moves above the soil surface and is more susceptible to frost damage and temperatures of 28 degrees can be damaging. However, when temperatures are below 50 F for several days before the frost, small grain crops go through a hardening process and develop more frost tolerance. Prior to jointing, hardened small grains have been shown to withstand temperatures as low as 14 F.

Spring small grains are still very young and therefore fairly tolerant to cold temperatures. For areas of the state most affected by freezing temperatures, the winter wheat crop has not started to joint and will also be quite tolerant. However, the cold weather was quite intense in areas of the state and there could be significant damage. To evaluate damage by frost it is best to wait two to three days so injury is more easily observable. Check to see if there is any new growth. If there is no re-growth in the affected plants, split the stem and inspect the growing point The growing point should be white or cream colored. Darkening or softening, with a watery appearance of the growing point, indicates injury and usually precedes plant death.

Joel Ransom
NDSU Extension Agronomist - Cereal Crops



Given the very dry spring that we have had so far in almost every region of the state, there is concern that water will be limiting for crop production this season. Crops differ significantly in their water requirements, drought tolerance and water use efficiency. Crop selection can be one way of matching water availability with crop requirement, though predicting the amount of moisture that is likely to be available in a given season is more often guesswork than science. Nevertheless, with low levels of stored moisture in the soil and the limited rainfall this spring, the water requirement of the crop to be grown should be given some consideration.

Strictly defining the water use by a crop is difficult as water use is affected by the amount and timing that water is available. For example, a crop like corn is water use efficient (produces more dry matter per inch of water),

but also has a relatively high water requirement as it has a higher yield potential than most crops. Furthermore, crops differ in how water stress might affect them. Corn, for example is very sensitive to drought during the flowering process. Wheat on the other hand, is sensitive during early vegetative development. A crop that is stressed early in its growth cycle, may not be able to recover to the extent that it will be able to use the water that is available, even though rainfall during latter stages of development is plentiful. Bearing in mind the difficulty of precisely defining in absolute terms that water use and water use efficiency of a crop, the following tables may be useful in categorizing crops as to their requirements in relative terms.

Total water is not the only criterion to use in selecting a crop for a dry season particularly if you have moisture deep in the profile. Crops differ in their ability to extract moisture from depth. The rank in rooting depth for crops is: safflower (about 6 ft maximum) > sunflower > small grains = canola > soybeans = dry peas = dry beans (about 3ft maximum rooting depth).

Table1. Approximate acreage yield, water use and water use efficiency of some crops commonly grown in the northern Great Plains.


Average Yield/A

Average Water Use, Inches

Water use efficiency yield/A/inch H2O

Grain Corn
Sugarbeets (Sugar)
Spr. Wheat
Pinto Beans

5 tons
120 bu
400 cwt
3.2 tons
35 bu
40 bu
1500 lb
25 bu
2200 lb


0.2 ton
6 bu
20 cwt
0.2 ton
2.2 bu
2.7 bu
110 lb
1.7 bu
180 bu
5 bu

Source: J. W. Bauder and M. J. Ennen, NDSU Soil Science Department.

Table 2. Water use by selected crops in 1999-2000.


Water use, inches

Dry Pea
Spring Wheat
Dry Bean


Source: Crop Sequence Calc., USDA-ARS Mandan.

Duane Berglund & Joel Ransom
NDSU Extension Agronomists


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