ISU Extension Agronomist Notes Some Alfalfa Winterkill Showing Up

Some alfalfa fields in northeast Iowa are showing signs of winterkill; ISU Extension agronomist points out some options.

May 05, 2013

As alfalfa fields wake up from winter and start greening up, the extent of winter injury to stands becomes obvious. For the past two weeks, some farmers in northeast Iowa have been reporting fields that are looking a little thin or have areas that didn't survive winter very well.

CHECK ALFALFA STANDS: Reduced alfalfa stands are showing up, having suffered from winterkill. Evaluate stands for density and for root health. Iowa State University has information online to help you evaluate alfalfa stands and other forages, too. It includes a table on alfalfa plant counts per square foot. An alternative method is to use stem counts. Once alfalfa plants reach 6- to 8-inches tall, you can count the number of stems per square foot for a better estimate of stand potential.

In late April, Brian Lang, Iowa State University Extension field agronomist in northeast Iowa, investigated some hayfields in Dubuque and Delaware counties. There was some alfalfa winterkill, with the majority occurring on south facing slopes of alfalfa fields seeded in the spring of 2012. There was also some Italian ryegrass winterkill on south facing slopes. The winterkill was rather spotty, anywhere from a few square yards to a few acres. Spotty enough in some cases to interseed, and in others widespread enough to start over or rotate the field to corn.

Interseeding alfalfa into alfalfa is okay within the first year of a seeding, says Lang. The nature of the kill on the alfalfa plants was tissue damage at or just below the crown of the plants. "When squeezing the taproot and crown, it should be firm," he points out. "The dead plant's crown and/or taproot just below the crown was soft and spongy. When sliced open, the tissue from the winterkilled plants was soft and yellow (maybe stringy) not firm and cream colored as it would be on healthy plants.

Evaluating alfalfa stands for number of live plants and for root health

When evaluating alfalfa stands, you can conduct a stand count to measure the density of the stand. Also, be sure to check the roots to see how healthy they are, advises Lang. Steve Barnhart, ISU Extension forage specialist, has posted information on stand evaluation of alfalfa and other forages in the ICM Newsletter here.~~~PAGE_BREAK_HERE~~~

That article includes a table showing alfalfa plant counts per square foot. "An alternative evaluation method that is more accountable then plant counts is to use stem counts," says Lang. "Once alfalfa plants reach 6- to 8-inches tall, we can count stems per square foot for a better estimate of stand potential. A University of Wisconsin publication explains the stem count method. To summarize, alfalfa stands averaging 55 or more stems per square foot are excellent stands.

More reports of winterkill of alfalfa and other kinds of forage seedings

Ryegrass: There have been a few more reports of ryegrass winterkill in northeast Iowa.

Orchardgrass: There are some reports of injury to orchardgrass from minor setbacks in growth to possible winterkill. "Orchardgrass varieties have a wide range of winterhardiness," says Lang, "so we could easily lose some stands to winterkill while others are just fine. When choosing an orchardgrass variety to plant, it is important to select among the more winterhardy varieties with medium-to-late maturity and good rust resistance."

Alfalfa: Alfalfa fields are greened-up enough now to tell the good from the bad. Even 'good' stands will likely have yield reductions in 2013 of approximately 10% of 'normal' because of the effects of the drought, winter conditions and a late start this spring, says Lang.

New seedings: There are more reports now coming in of winterkill to new seedings and the winterkill is not limited to the south slopes.

Older stands: More injury is being noticed on older stands beyond the obvious ice sheet problems. Combinations of stress factors are resulting in variable and patchy injury to plants across alfalfa fields.

Potential stress factors in alfalfa. The more stresses an alfalfa stand is exposed to, the greater the risk of winter injury:

1) Ice sheets in lower areas of fields

2) Wheel tracks.~~~PAGE_BREAK_HERE~~~

3) Harvest frequency

4) A fall cutting that does not allow enough time to replenish carbohydrate reserves going into the winter

5) Lack of stubble left in fall for cover/insulation during winter

6) Lack of insulating snow:

a) Too much ice too long especially in low areas of fields. Stubble reduces the chance of this kind of injury.

b) Fencelines and leeward slopes (usually south and east) are more protected. Usually! But not so much this past winter with south slopes.

c) Air temperatures too cold too long are often tied to windward slopes (usually north and west) that lack snow cover. Or it can be tied in with ice formation (ice conducts cold air temperatures; ice is not an insulator).

9) Inadequate pest management during the season (i.e. potato leafhopper)

10) Too difficult to really know in 2012, but at what point was drought stress too severe when combined with other stresses?

What to do? Evaluate your forage stand this spring, then sort out options

Lang offers the following "short list" of options to help you deal with injured alfalfa stands. Those options include:

1) New seedings of alfalfa can be interseeded with perennial forages including alfalfa. Autotoxicity with alfalfa is a minimal concern if you interseed within the first year of establishment.

2) Start over with a new seeding again. Autotoxicity with alfalfa is a minimal concern within the first year of establishment.

3) Older stands could be interseeded with Italian ryegrass in an attempt to boost yield in this last year of production for that stand. Most of the yield contribution will be with third and fourth crop of hay.

4) Rotate failed new seeding field or an older stand to corn silage.

5) Keep a somewhat questionable alfalfa stand for first crop harvest. Then rotate the field to a shorter season corn silage hybrid.