Winter Storm Informaton

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Spring Frost Damages to Field Crops

Temperature 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 the cells have built in anti-freeze 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.

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 to 8 inches tall (five-leaf stage or less) will recover from frost because the growing point is still below the soil surface and usually not damaged. 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 that 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, slowly rising temperatures after a frost and satisfactory soil moisture conditions are desirable to aid recovery. Drouth, wind and high evaporation are likely to aggravate the frost injury and lessen the chances of recovery.

Our cereal grains will lose leaf tissue that freezes. New growth will follow as the growing point before jointing is protected below ground. In some cases the eventual maturity date may be delayed. For example, a 80 day corn that has a couple leaves froze off may in fact mature like an 84 day corn.

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. Soybeans may leaf out again after a light frost from axillary buds in the leaf axil. One of these branches will then become the main axis of the plant if the first growing point is killed.

Dicotyledonous plants such as sugarbeet, sunflower, soybean, dry bean, canola and flax are more easily killed by frost than are small grains. Sunflower in the cotyledon stage may often withstand temperatures as low as 26 degrees F. Sunflower in the 2, 4 and 6 true leaf stage becomes more sensitive to frost and bud damage may occur.

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. I feel that in the 2-leaf or V2 stage then 26-27 F would be the lower limit. For the 4 and 6 leaf stages then 28-29 F as the lower limit.

Also the tolerance also 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. Its going from warm temps to extreme freezing temperatures all at once 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 coming out of the ground. It can, in some cases, tolerate temperatures of 28 degrees F if it has a couple of true leaves. Depends some on growth conditions the previous couple days. Check to see if stem is turning black. After 2-leaf stage and hardened off it can stand temps in low 20's.

Alfalfa will be damaged by temperatures in the mid 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. Temperatures of 32 degrees F and below will kill buckwheat or drybeans, and temperatures of 29-30 degrees F for soybeans, while alfalfa, canola, crambe, flax and sugarbeet will tolerate temperatures in the mid 20's. Crops such as field peas or lentils have good frost tolerance since several growing points remain below ground in the seedling stage.

Broad leaf crops that have their growing point (terminal bud) at the top of the plant are more susceptible to frost damage than our cereal species. Beans for example are quite sensitive to frost. Beans may leaf out again after a light frost from axillary buds in the leaf axils. One of these branches will then become the main axis of the plant if the first growing point is killed.

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