Wild Winter Temperature Has Different Effects On Forage Crops

If plants were well established prior to the onset of winter and had the opportunity to harden and tiller, chances of survival are very good, but forage production may be impacted.

This year's unusual winter has led to questions for farmers and ranchers who grow forage crops in North Dakota. The lack of snow cover has left winter crops uninsulated from cold temperatures for much of the winter. Recent extreme temperature fluctuations have led to concerns about possible damage to winter annual cereal crops planted for forage late summer and early fall.

Two of the most common winter annual cereal crops grown for forage are rye and triticale. Cereal rye is the most winter hardy of the cereal grain crops and can grow at a temperature as low as 38 degrees Fahrenheit, according to James Rogers, North Dakota State University Extension forage crops production specialist. Winter wheat is less winter hardy than rye but more tolerant than barley. Triticale, a hybrid cross between rye and wheat will have more cold tolerance than wheat but less than rye. Triticale's cold tolerance is based on its wheat parentage.

"Optimal spring growth for cool season crops is 65-75º, but recent temperatures reaching into the 50s have stimulated top growth of these forages," Rogers says. "Then, with the sudden reversal of temperatures down into the low teens, plant damage and winter survival concerns arise. In general, however, if plants were well established prior to the onset of winter and had the opportunity to harden and tiller, chances of survival are very good."

Research from the NDSU North Central Research Extension Center in Minot reveals differences in freeze damage between rye and winter wheat.

On March 1, researchers at the center dug a sample of rye plants from a plot planted in July 2023. The plants were exposed to a high daytime temperature of 53º Fahrenheit on Feb. 26 followed by a high temperature of 7º on Feb. 27. The researchers then dissected the plant tillers by splitting the tiller beginning just above the crown to the top of the tiller, exposing the growth point, which was at the very base of the tiller, just below the soil line. The growth point appeared as a healthy dark green oblong mass sitting just above the crown of the plant at soil level.

"At this low location, the growth point is still protected by the crown, and any additional snow cover this spring will further insulate the growth point," Rogers says. "Top growth did show some browning of leaves from freeze damage, but other leaves were green, and new growth was evident. Additionally, roots of the plant were white and healthy, and new tillers were forming. As the growth point begins to elevate with warmer temperatures, the plant and grain formation will become more vulnerable to freeze damage."

As a contrast, researchers also dug up a sample of winter wheat from a plot planted in June 2023. They dissected the plants and found that the growth point of the wheat was at the very base of the tiller, similar to the rye sample, but the winter wheat plant had been damaged to a much greater extent by freezing temperatures.

"Some roots were white and healthy, but others were dark and brown indicating freeze damage," Rogers says. "This plant may still recover, but forage production will be reduced."

Winter-established cereal crops become more vulnerable to freeze damage at jointing and elevation of the growth point, which may cause the loss of individual tillers but not the whole plant. Tiller production is key to biomass production.

"It is still too early to determine the full extent of possible freeze damage, but optimism remains," Rogers says. "At this point, if the current snow cover dissipates, more damage may occur from ground heaving than from freeze damage."

To monitor growth points as spring approaches, cut a sample of tillers at the soil level and split the stem. Locate the growth point in the tiller. As the growth point elevates, the stem will be hollow beneath the growth point. When this hollow stem reaches the diameter of a dime (5/8 inch), the stem has elongated prior to stem jointing. At this point, plants can experience damage to the growth point at temperatures of 10-20º Fahrenheit.