Researchers offer solutions for alfalfa winterkill

By Kylene Orebaugh

Winter precipitation can be good for spring crops. But what happens if the weather gets too cold or the standing water or snow sticks around too long on alfalfa fields or if the crop is drought-stressed prior to winter weather? Some research shows winterkill could be a problem.

What is winterkill?

As one of the most important legumes in agriculture, alfalfa is commonly fed to livestock and horses since the cool season legume is highly coveted for its protein value. Put quite simply, alfalfa plants can be killed by cold temperatures.

Killed plants will have gray roots that may appear to be water logged. Once the water is gone, the root tissue turns brown, looks dehydrated and stringy.

The plants can also have frozen crowns, as well as a soft mushy taproot (located just below the crown). Some plants will initially green up, but then die. Those plants with second leaves normally are not affected by winterkill.

Winter hardiness in alfalfa is determined by a couple of things, Dan Undersander, University of Wisconsin-Madison, Extension forage specialist writes.

--Freeze tolerance. Currently, researchers think the plasma membrane (the structure around the perimeter of the cell, just inside the cell wall) is the primary site of injury. Cold-adapted plants have evolved mechanisms to allow either supercooling of the cell solution or to initiate ice formation in the extra cellular spaces rather than inside.

--Cell rupture. Damage can occur when the extracellular ice grows and crushes tissues, causing plant damage.

--Dehydration. Damage from the cell membrane breakdown during the thaw release toxins which kill the tissue. This is why plants often look healthy until spring greenup, Undersander said.

"Consequently, superior cold tolerance of alfalfa relates to factors controlling the location, the growth rate and the propagation of ice within the plants and among molecular changes that will help stabilize membranes and proteins in the dehydrated state," Undersander said in his paper, "Understanding Alfalfa Winterkill."

For a photo of freeze injury visit http://www.uwex.edu/ces/crops/uwforage/StandEvaluationFOF.htm.

To evaluate stands, estimate the number of live plants per square foot. Extension professionals say the best way to do this is to dig up and count the plants in a 1 to 2-square foot area in several parts of the field. Second year stands should have around 10 to 12 plants per square foot, while third year stands about half that. When making counts, consider only those plants that appear healthy and have vigorous shoot growth. Make a further inspection of the taproots, and condition of new buds and shoots. Healthy plants will be vigorous and symmetrical.

Degrees of damage seen

In late April, forage specialists around the High Plains area were seeing varying levels of winterkill. Some stands were killed outright, while others suffered varying degrees of damage.

"The winterkill from this past winter was located mostly in low spots within fields," Bruce Anderson, professor of agronomy and Extension forage specialist from the University of Nebraska said. "It also was on heavier-textured soils with poorer drainage."

In many areas, the Easter freeze of 2007 followed by dry conditions left many stands weakened. This left the perfect set up for winterkill. However, late winter and early spring weather conditions did not help matters much, either.

"In all probability, abundant rains late last season sent some of this alfalfa into winter with water-logged soils. Other areas may have developed ice following a winter rain or snow melt that froze before it could drain away," Anderson said. "These conditions can cause alfalfa plants to essentially suffocate over winter due to an inability of the soil to exchange air gases with the atmosphere. The roots need oxygen to maintain respiration over winter and toxic gases that are produced during respiration need to dissipate."

So what should producers look for? Careful inspection of fields at this time is important and actually getting out in the field to look at the stand as well as individual plants is a good idea. This should give producers a good idea if the whole field or just parts of it are affected.

"Most of the field will green up as expected but low areas will stay brown or sometimes green up very slowly and with thinner stands," Anderson said. "(Next) determine if the field as a whole is worth salvaging or if it is better to plant to a different crop, like corn."

Solutions for the surviving stands

In late April, the Kansas Department of Agriculture market news reported alfalfa production was projected to be down. Demand was also anticipated to be strong for new crop alfalfa of all grades. Similar reports came from other surrounding states. So with the strong demand, what should producers do to keep customers happy and have supplies to feed their own livestock? Anderson suggested a couple ideas.

--Reseeding young stands with alfalfa.

--Interseeding with another crop.

--Wait until late summer to replant alfalfa stand.

--Plant another perennial grass.

Only young stands should be reseeded, Anderson said.

"Fields only one, or maybe two years old can be reseeded directly, which usually is the best solution in order to keep the field all under similar management," Anderson said. "Older stands may have problems establishing a new stand due to autotoxicity problems with planting alfalfa after alfalfa."

If the stand is older, consider seeding with another legume to produce some hay.

"In these situations, it might be better to seed red clover if an all-legume hay is desired. Autotoxicity won't affect red clover," Anderson said.

He also suggested oats and Italian ryegrass, but they come with planting stipulations, and both need good moisture levels.

"Most producers who desire increased yield for this year should plant a summer annual grass after first cutting," Anderson said. "Sorghum-sudan grass, cane, pearl millet, foxtail millet, and teff all are possible options."

Another solution to replace winterkilled alfalfa is to wait until August to replant. Producers could replant with alfalfa or another perennial grass like orchardgrass, brome, fesuce or wheat grass.

Kylene Orebaugh can be reached by phone at 620-227-1804 or e-mail at kscott@hpj.com.

6/2/08
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Date: 5/29/08

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