Many livestock producers are questioning whether their alfalfa stands are at risk of winterkill. In early January, many fields were covered with an inch or two of solid ice.
Ice sheeting may raise the risk of winterkill in alfalfa. But snow cover and continued cold probably won't to worsen winterkill and may actually protect alfalfa. So the answer is: "It depends."
* How old is the stand? Alfalfa stands often become thin and less productive after the third year. Harsh winter conditions can exacerbate this decline with advancing age.
Plants that are one- to two-years old are generally more stress tolerant than older ones. That's because they've been exposed to less physical damage and disease.
* Plant genetics matter. Varieties vary in winter hardiness plus resistance to diseases and pests. Choosing a variety that resists diseases such as phytophthora and verticillium, bacterial and Fusarium wilts reduces the risk.
* Field fertility also matters. Soil pH below 6.0 stresses alfalfa plants and can exacerbate winter injury. A soil pH of 6.6 or greater removes this risk.
High exchangeable soil potassium (greater than160 ppm) reduces risk of winterkill and conversely, a low exchangeable K (less than 80 ppm) can make winter injury much more likely by reducing root health and fall carbohydrate storage.
* When did you take your last fall cutting? Leaving a 6- to 8-inch stubble in the fall may have helped catch snow before the icing. That snow layer may help insulate the plants.
Now, about ice sheeting . . .
Alfalfa stands typically don't survive well on poorly drained soils. If water accumulates and freezes on the plants and soil surface, ice sheeting can occur in low areas during a mid-winter thaw or from sleet and freezing rain.
Ice sheets essentially smother plants. The longer the ice remains, the greater the risk of economic damage.
This winter, however, at least in northern New York, that ice is on top of several inches of snow. So the alfalfa crowns and roots may actually be insulated from the polar cold and high winds.
If ice formed directly on the alfalfa crowns and soil, no such protection would occur. The plants would be at risk of smothering and loss. In lab research trials, alfalfa plants directly covered with ice began to die after about a week. Most were dead within a month.
To learn more, check out these website resources:
* Evaluating alfalfa winter injury: forages.org/page.php?pid=44.
* Calculate alfalfa winter injury risks: www.uwex.edu/ces/forage/pubs/winter.htm.
* Managing alfalfa stands after winter injury: www.uwex.edu/ces/crops/uwforage/StandEvaluationFOF.htm.
Information provided by Kitty O'Neil, a Cornell Extension field crops and soils specialist in northern New York.