Jerry Cherney, Leon Hatch and Ed Goyette

Dept. of Soil, Crop & Atmospheric Sciences

The immediate devastation from the January ice storm in the upper Northeast was obvious. The effect that the lingering ice has on survival of perennial forages, particularly alfalfa, is much less obvious. There certainly is the potential for severe winter damage, but damage can be increased or reduced by a number of factors other than the actual ice cover. Also, the worst part of the winter is often late winter, as far as conditions encouraging winter damage are concerned.

Last winter 1-2 inches of inches of ice covered central Wisconsin in late January and lasted till late March. Farmers were told with confidence that all their alfalfa was likely dead. Ice sheeting on top of alfalfa for more than 30 days should result in almost complete winter kill. Most of their alfalfa, however, actually survived the ice cover. On the other hand, winter damage in the state of Maine last winter killed most of their alfalfa and some of their orchardgrass. Vast acreages of alfalfa in southern Canada have been killed out in recent years due to ice sheeting and cold temperatures. Winter damage is just not very predictable.

Ice sheeting can result in winter kill by smothering plants over a period of time. Very low temperatures following ice sheeting can result in rapid killing, as cold temperatures are easily transferred through ice to the plants. The longer that ice remains, the greater the chances for damage. When alfalfa plants are covered with ice in laboratory studies, plants start dying after about a week, and most are dead in 30-40 days.

The survival of alfalfa is based on the plant’s ability to survive a specific combination of stresses in any given winter. Some of the stresses besides ice sheeting include cold temperature, fluctuating temperatures, lack of snow cover, high soil moisture, low soil fertility, and previous harvest management. Ice sheets formed on frozen soils with low soil moisture, followed shortly by snow cover on the ice, are less likely to do damage. The actual porosity or density of the ice will affect survival. For example, we have observed that ice now on fields in Clinton county is very hard and dense, while ice on fields in St. Lawrence county appears soft and less dense. If there is a snow layer between the ice and soil, chances of alfalfa survival are increased. A snow layer between ice and soil was considered the likely reason alfalfa survived prolonged ice cover in Wisconsin last winter.

Alfalfa varieties with a higher degree of fall dormancy will have a better chance of survival. The age of a stand will affect survival, as will the relationship of the alfalfa crown to the soil level. The older the alfalfa stand, the more likely that insect and disease damage may have weakened plants, such that less stress is necessary to kill them. The more harvests taken the previous season, the more prone the stand is to winter damage.

The mechanical force or weight of several inches of ice does not appear to have any effect on plant survival. Neither does the presence of alfalfa stubble sticking through the ice affect survival, according to past research. Stubble height will affect survival, however, by increasing the chances of snow cover.

Prior to spring, about the only method of estimating damage due to smothering from ice is to actually dig up frozen plants and put them in a greenhouse for evaluation. Plants will green up in a week or less, if alive. We are using a concrete cut-off saw to extract samples from ice-covered fields in northern New York, and it is a tedious process. While this provides an assessment of damage to-date, it does not tell us how much of the alfalfa alive now will actually survive the rest of the winter.

Although the ice storm gives the appearance of a uniform conditions, with ice covering everything, conditions are actually quite variable from the alfalfa’s point of view. Fields sampled at Miner Institute in Clinton county had about 1.5 inches of ice cover, usually with snow trapped between the ice and soil. Fields sampled in St. Lawrence county had 2-3 inches of ice cover directly on the soil surface. Some fields have an air pocket several inches thick between the ice and soil, due to snow melt between ice and soil. Some fields are frost-free, others have frost deeper than 6 inches. Snow cover above the ice in late January varied from a few inches to over 30 inches.

Scientists working for Agriculture Canada have developed a method for evaluating low-temperature winter injury to alfalfa. Roots and crowns are evaluated as soon as the soil thaws out in the spring. Three criteria are used: bud vigor, root resistance to peeling, and root interior color. Bud vigor is rated from 1 (obviously dead, brown) to 4 (firm, white or pink). The root surface is scratched with a thumb nail and rated 1 (low), 2 (medium), or 3 (high) for resistance to bark peeling. Root interior color is rated from 1 (brown) to 3 (white or cream). A combination of the three criteria results in an estimation of winter injury due to low-temperatures.

Grasses are less susceptible to winter damage than alfalfa, but it is possible that there may be winter damage to grasses due to the ice storm, particularly with orchardgrass. The full extent of the perennial forage crop damage from the ice storm will only be fully realized until first harvest in late spring.