May 22, 2003

 

Heavy Frost Causing Producer Concerns

A recent heavy frost has some producers concerned about crop damage. The areas hardest hit were in western and certain northern areas of North Dakota. Temperatures on Tuesday morning reached a low of 22 degrees in Bottineau and 20.3 degrees in Golden Valley County.

We’re not expecting a significant percentage of loss but we’ll know more as the days go by," according to Kent McKay, Research Extension Center area agronomy specialist in Minot. "Temperatures below 28 degrees for a period of four to six hours can cause serious damage."

McKay, NDSU Extension Service forage specialist Dwain Meyer and NDSU Extension Service agronomist Duane Berglund have some advice for producers when scouting for frost damage.

Small Grains: "Small grains are very tolerant to temperatures as low as 22 degrees," McKay says. "Keep in mind that the growing point is below the soil surface until the five leaf stage. The only significant damage that could occur is if the frost was hard enough to collapse the stem which would cause the plant to wilt and most likely die."

In most instances, wilted, dark green and discolored leaves will be the normal appearance. Recovery is usually quick with a new leaf, normal green in color, emerging from the stem within two to three days.

For winter wheat the extent of time that the plants were subjected to the cold temperatures will be the issue, Berglund says. "In the worst case scenario, the developing spikelets will be injured to the point that no kernels will develop. The top of the head and awns will turn white."

Canola, Flax, Mustard: These crops can handle temperatures down to 24 degrees for a short period of time according to McKay. Canola is the most tolerant to cold temperatures. Plants with frost damage will turn dark green or black. "If plants do become discolored, growers still need to wait two or three days before any decisions are made. If the plant is still alive, a new leaf should emerge from the growing point located in the center of the plant."

The best indication that the plant has been killed is by observing the stem. If the stem below the cotyledons is wilted and doesn’t straighten out within 48 hours after the frost, the plant is most likely dead.

Pulse crops including field peas, lentils and chickpeas: Similar to small grains, the growing point is below the soil surface to the fifth node stage or about the 4-inch height stage. If the stem is collapsed or wilted for 48 hours with no regrowth apparent, the plant is most likely dead. The recovery period is usually quick for plants that have survived. A new leaf should emerge from the stem within three days.

Sunflowers: "Sunflowers, when in the cotyledon stages, can withstand temperatures in the 25 to 26 degree range for a short period of time," Berglund says. "Leaves in the 2-, 4- or 6-leaf stages become more sensitive with each stage and the terminal bud can be permanently damaged. It’s believed that when sunflowers are in the V2 stage, the lower limit is 26 to 27 degrees. Sunflowers in the V4 or V6 stage have a tolerance level of 28 to 29 degrees. If sunflowers become brown or black and the terminal bud is damaged, the plants will not recover."

Corn: "The key to assessing corn seedling viability is to find and observe the growing point," according to Berglund. "The growing point is where all new tissue originates and is protected below ground until the plant reaches the V5 stage. The death of leaf tissue above the growing point has only a small effect on corn growth and yield but it may slow the development process." The five-leaf stage is when corn is 6 to 8 inches in height.

The growing point can be found by pulling the entire corn plant, including roots and splitting it lengthwise. "If the growing point was below ground and is white or creamy in appearance, then injury did not occur," Berglund says. "However observations for frost damage are best made by waiting at least two or three days after the frost. At that time, if the growing point is white to yellow in color, full plant recovery is likely. Even plants with extensive leaf tissue damage will likely recover if the growing point is not injured. New leaves should appear within three to four days."

Alfalfa: "A variety of factors such as the maturity of the alfalfa, duration of freezing temperatures and soil water level will determine the scale of damage," Meyer says. "Generally it takes colder temperatures to kill an alfalfa stem. I have seen alfalfa survive a 14-degree frost with less than 30 percent stem kill."

A hard frost will cause the alfalfa stems to "shepherd hook" or act as a lazy stem. If the stem straightens after a warming period, then the stem is not injured and growth will resume.

"If the stem does not straighten out, then it has been killed and the plant will start to dry out or turn a whitish color," Meyer says. "The alfalfa should be harvested assuming enough growth has occurred. Nothing needs to be done if the alfalfa is less than eight inches. The alfalfa will recover from the active auxiliary buds on the lower portion of the plant or from the crown. I don’t recommend clipping the plant. It won’t hurt it but it won’t help either."

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Source: Kent McKay, (701) 857-7682, kent.mckay@ndsu.nodak.edu
Duane Berglund, (701) 231-8135, dberglun@ndsuext.nodak.edu
Dwain Meyer, (701) 231-8154, dwain.meyer@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu