North Dakota State University Extension Service - Burke County |
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Burke County AgAlert |
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May 13, 2004 FROST/SNOW? What can impact injury? How different crop species react to freezing temperatures depends on where the growing point is and how much growth has taken place. Seedlings that have been acclimated or "hardened" by cold temperatures will be more tolerant to extremely cold temperatures. Wet top soil and/or snow is desirable if a hard frost occurs. Snow will actually insulate the crop from freezing temperatures. Fields with heavy residue are more prone to be colder under sub-freezing conditions than fields that lack residue. Fields that lack residue will radiate some heat reducing the impact of an extended frost. Most early seeded, cool-season crops can withstand temperatures as low as 25 F for a short time. If temperatures dip below 25 F for several hours that’s a "freeze" not a frost and damage will be more significant. If temperatures drop below 20 F, frost damage to all crops will be severe. CANOLA: The growing point is above ground once the cotyledons emerge. Canola in the cotyledon stage can withstand temperatures as low as 22 F; especially if the plants have been hardened to sub-freezing temperatures. If temperatures fall below 25 F for an extended time there most likely be some level of injury. When evaluating frost injury, a waiting period of three to four days is needed to see if the growing point is alive. If the growing point is a light green fleshy color, the plant is alive. If the growing point is black or a dark green color, then most likely the plant is dead. The stem of dead plants will be wilted, black in color, and will be laying on the soil surface. A good sign that the plant will recover is that after 3 days a new leaf will be emerging in the center of the growing point. Often the older leaves or cotyledons will wilt or even die and the overall appearance of the field will look tough, if the growing point is alive the crop will recover. Tame mustard is not as tolerant to a hard frost as canola; however, it is more tolerant than flax. FLAX: The growing point is above ground once the cotyledons emerge. Flax that is in the cotyledon stage is not as tolerant to a hard frost (below 25 F) as canola. Flax that is in the 2-leaf stage and has hardened off can stand temperatures in the low 20's. Similar frost evaluations and injury symptoms for flax are described in the canola section. FIELD PEAS AND LENTILS: Field pea and lentil have similar emergence as small grains. The growing point is below the ground with the seed piece until the peas or lentils are in the 4th node stage or 4 inches high. Peas are very tolerant to a hard frost and are more tolerant than other broadleaf crops. If temperatures fall below 20 F, stems/plants will wilt and appear to be severely injured; however, recovery should be fast due to the fact the growing point is below the ground. SMALL GRAINS/CORN: Small grains/corn in the 1 - 4 leaf stage can handle temperatures in the low 20's without major injury. If temperatures fall below 20 F, that is considered a severe frost. Emerged leaves might wilt or even die, however a new leaf should begin to emerge 3 to 4 days after a severe frost has occurred. Small grains in the jointing stage (4 ½ leaf barley, 5 leaf wheat) or corn that is in the 5 leaf stage will be more sensitive to a frost for the growing point is now above the soil surface. Once the crop hits the jointing stage, the growing point is above the ground and the length of the frost is the question, not how cold it was. Winter wheat is also very tolerant to cold temperatures, especially if it has been hardened off. As long as the winter wheat has not reached the jointing stage, minimal injury should occur. ALFALFA: Alfalfa seedlings can handle temperatures in the 20's. If 6 to 8 inches of the top growth is injured and has an apparent "shepherds hook" the crop will reinitiate growth from the crown. This means that a salvage harvest needs to done for the crop will drop all its leaves and if not harvested the first cut will be lost. Dan Folske |
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