Winter Injury to Forages, Wheat and Rye

Ohio is no stranger to a wide range of fluctuating winter conditions. After the recent spell of cold and snow in Ohio, we are now looking ahead to rain and warmer temperatures. While this relief from the winter elements may be appreciated by many, this flip of conditions can result in some challenges with our over wintering grain and forage crops.

Dennis Pennington, a wheat system specialist from Michigan State University shares some of the details on why crops such as wheat need the cold weather and why the break in cold temperatures can cause problems.

Pennington, on wheat states, “Winter wheat goes through a vernalization period where the plant hardens and adjusts to the colder winter temperatures. The hardening off period begins in the fall once temperatures at the crown (growing point, generally placed about 1-2 inches below ground surface level) drop below 48 F and continues as the temperature decreases. The hardening process causes a reduction in moisture content in the cells of the crown which slows growth processes and the accumulation of soluble carbohydrates, all of which help the plant to resist frost damage.”

Dennis goes on to discuss the hardening process, as he states, “The hardening process takes place over four to eight weeks and the level of hardiness is directly related to the soil temperature at the crown depth. Daylength also impacts hardiness, as shortening days in the fall induce wheat winter hardiness. Conversely, longer days in spring bring wheat out of hardiness. Cold tolerance is dynamic and can be lost if soil temperatures rise above the previous temperature that the plant hardened to. According to a study by D.B. Fowler from the University of Saskatchewan in 1982, if the crowns of the plants are exposed to warmer temperatures for as little as 50 hours, the cold hardiness can be decreased substantially. The loss of cold tolerance has several major implications.”

Winter wheat greening up in the spring. Some tip die-back is visible in this photo.

The two major implications that Pennington describes in his article are the following: First, if soil temperature decreases below the current level of winter hardiness, injury will occur. Secondly, once a crop loses winter hardiness, it will never reach the original level of hardiness and it will de-harden more quickly each time the soil temperature rises above the minimum survival temperature.

As pointed out by Pennington in his article, what you want to see is a steady line in the temperature, without large spikes in either direction. Whenever the temperature spikes up followed by a spike down below the original temperature, injury can occur.

Generally speaking, when looking at the crops that are over-wintering in the fields, snow melt can be a concern. Obviously, warm weather causes the snow to melt. Snow, however, serves as an insulator and can protect the crowns of plants against major swings in air temperature. Snow melting can also result in ponding in the fields. In cases where drainage is adequate, there should be little to no concerns, but where water persists, evident by ponding or high levels of field saturation, waterlogging may occur. Additionally, if the water persists, the crowns may absorb more water, which could be problematic should conditions become cold again as it would result in cell rupture when the water in the plant freezes and expands. Ice damage can also occur in areas where standing water freezes over dormant plants for an extended period of time, essentially suffocating them. There is really a wide range of problems that can occur when we have a significant amount of snow the melts off before we are safely out of reach of winters grasp.

An example of how far an alfalfa plant can be heaved out of the ground via several rounds of freeze/thaw cycles.

Another concern, especially in forages, is heaving. Now that the ground is exposed, should we get back into a freeze/thaw pattern, heaving could occur. Heaving occurrence can increase significantly in areas of fields where there is a lot of moisture, and with the recent snow melt, there are a lot of fields with excess moisture.

Getting closer to spring, these issues may not be anything to worry about, but certainly something to be aware of. Worrying about temperatures will do nothing to change them, and this area of crop production is unfortunately out of our hands but being aware of these concerns can help you assess damages should any occur. Getting out to scout alfalfa, wheat and rye fields in the spring is recommended, not only this year, but every year. Evaluating your fields as early as you can in the spring can help you make efficient and impactful management decisions and consequently, take action if warranted.

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