Freeze: Forage Friend or Foe

Urbana, Illinois (February 1, 2007)--Will the freezing rain and icy weather harm my alfalfa? What about my wheat crop? These are good questions in light of a recent ice storm and cold weather in western Illinois.

An alfalfa plant and its root system require an exchange of carbon dioxide and oxygen gases for growth even during winter months. When a uniform sheet of solid ice covers the ground and plant without any cracks or holes, the level of carbon dioxide around the plant and roots can increase and the amount of oxygen decrease. This decrease in oxygen can result in alfalfa plant tissue decline and death. However, plant stubble protruding through the ice will help encourage oxygen exchange. The temperature of the ice really does not harm the plant, but air temperatures less than 15° F can damage alfalfa crowns even when plants are well hardened off.

Injury from ice is less likely when good cultural practices are followed that promote healthy plant growth. Alfalfa plants and root systems are healthier when they receive proper amounts of fertilizer based on a soil test; when they are cut properly to allow carbohydrate levels in roots to accumulate in the fall; and when they are hardened properly.

Wheat plants also need oxygen during winter months and plants can suffocate when soils become waterlogged or flooded fields freeze. Wheat plants that are not completely dormant, which may be the situation in some locations due to the mild temperatures in mid December, are prone to suffocation after a few days without oxygen. Similar to alfalfa fields, wheat fields with plants protruding through the ice are more likely to permit oxygen exchange.

Disease is another issue facing both crops. Snow cover often insulators plants protecting them from desiccating winds and low temperatures, however, when snow persists and ice is present plants become stressed and more susceptible to disease. For example, snow mold on wheat is caused by several fungi that live under the snow near the soil. It is best to examine wheat plants under the snow or wait until after the snow melts to view symptoms. If snow mold is present, the wheat plant will be covered with slimy fungal growth, and brown or black circular fungal fruiting bodies, which look like small animal droppings, may be present. Wheat leaves will generally look brown, flaccid, and rotted. If the wheat crown is infected the plant can die. However, if the wheat crown is not infected, plants can recover and produce adequate yields even with substantial leaf loss during the winter.

Nothing can be done to save plants from ice damage. Using a tractor and disc to break up ice generally does not help. An application of fertilizer with the thought that it might melt the ice due to the salts in the fertilizer is not a good idea either. Fertilizer does not totally melt ice and fertilizer deposits on top of ice can lead to substantial runoff problems. At this time the best advice is to wait. See how long the ice and snow last and then assess any damage that may have occurred.