Monday, April 21, 2014

Winter Injury in Perennial Forages

Two weeks ago Rory Lewandowski described in this blog how to evaluate forage stands for winter injury. So our question is, “Have you walked out into your forage stands yet this spring?” If not, you may be in for a rude surprise.
The hard freeze lst week was cause enough for concern for us to check a few fields. There is some frost dieback of the top leaves, particularly in orchardgrass (see photo).

Notice the yellowish tinge to the orchardgrass in the foreground compared with darker green tall fescue in the background that suffered less frost injury.
But the more serious problem we observed when looking around was severe heaving damage in alfalfa, particularly in the Wayne county, OH area. Some fields showed heaving of 70% of the stand.
Plants with crowns heaved up 2 or more inches out of the ground are probably already dead like in the photo above.
Heaving is usually more severe in areas with less than ideal internal and surface soil drainage and on soils with high shrink/swell potential. Tiling will likely help improve the alfalfa production potential of those soils, but heaving can still occur on certain soil types even when with tiling.

Heaving is also more likely where a mid to late fall harvest was taken. Fall harvesting can weaken plants and the removal of plant residue late in the fall can dramatically increase the potential for heaving, because the residue serves to moderate soil temperature fluctuations and catch snow that also insulates against wild temperature swings during the winter.

Plants heaved 1.5 inches.
 Some plants will be heaved 1 to 1.5 inches above the soil surface or less. These plants may on casual inspection appear normal and be greening up. But closer inspection will reveal crowns above the soil surface, which will likely limit the productive life of the plant.

Heaved plants will desiccate more quickly, be injured by wheel traffic, and crowns may break or be cut off at the first harvest. Some of those plants may survive through the first harvest, but their yield potential is compromised and they will likely disappear from the stand at some point during the growing season.
Plants heaved to varying degrees, starting to greenup.

Can anything be done to help heaved stands? Dan Undersander has written a very useful fact sheet about heaving that can be found here. He suggested that if the majority of plants are heaved an inch or less, that the taproot may not be broken and the stand has a better chance of being salvageable for this year. In this fields, delay the first harvest to allow more recovery time and raise the cutter bar sufficiently to avoid scalping the crowns. He also states that the stand should not be rolled or cultipacked, as this will only damage the crowns.

We also observed severe winter injury in some perennial ryegrass varieties and even in some white clover varieties in our trials. Time will tell how much they will recover, but the winter damage was quite substantial in some varieties, including an older perennial ryegrass check variety we use in our trials.

Literature Cited
Undersander, D. 2009. Heaving in alfalfa fields. Agronomy Advice. Agronomy Dept., University of Wisconsin. Available online at

Saturday, April 12, 2014

Evaluate Alfalfa Stands for Winter Injury

                       Rory Lewandowski, Extension Educator Wayne County
            As alfalfa stands break dormancy and begin growth, growers should make plans to take some time to evaluate the health of those stands and determine if there was winter injury.  Some early bud growth was observed the last full week of March in the southern half of Ohio.  This evaluation is especially important in those areas of the state where we had periods of near zero to below zero temperatures this winter combined with little to no snow cover during some of those cold temperatures.   After doing a quick literature review, it appears that there is general agreement that temperatures in the 5 to 15 degree F range as measured at the alfalfa crown can begin to damage the plant and prolonged exposure to these and lower temperatures can kill the plant.  Generally, the soil temperature at a 2 inch depth is associated with the temperature of the alfalfa crown.  Snow cover is an important component of protecting an alfalfa plant from sub-zero temperatures since even a cover of 4 inches of snow can provide 10 to 15 degrees of protection.  Once again, the concern is for those areas that experienced periods of zero and subzero temperatures without a 4 inch or greater snow cover.  For many areas of the state, however, soil temperatures at the 2-inch depth remained at or above 26F even through the coldest days this winter.
            An alfalfa stand health evaluation and winter injury assessment needs to be done by getting out into the field and doing a combination of stand counts and digging up some plant roots.  Generally that evaluation should be done when there is 3 to 4 inches of growth from the plant.  Evaluation involves selecting random sites throughout the field and counting the plants in a one foot square area.  Check at least one site for every 5-10 acres, and like soil sampling, more random sampling is better.  In addition to counting the plants per square foot, a count of the total stems per square foot is also useful because healthy plants can often produce more stems per plant thereby compensating for potential yield loss from fewer plants per square foot.   After counting the plants, dig up all the plants in a one foot square area for every 5 to 10 acres and examine the crown and roots of the plants.
            The winter survival rating determined by the plants per square foot is based upon the age of the stand.  The following table is from a 2012 article on the Iowa State University (ISU) Integrated Crop Management web site by Stephen K. Barnhart, ISU Extension forage specialist.

__________________Plants Per square foot_____________________
Stand Age
Consider reseeding
Year after seeding
Less than 8
2 years
Less than 5
3 years
Less than 4
4 years and older
Less than 3

            As mentioned previously, counting the total stem number in a square foot is another method of evaluating winter survival and yield potential of a stand and has been promoted by Dan Undersander, Extension forage specialist at the University of Wisconsin.  Here is a summary of that system:

Stem number/square foot
Expected result or action
Over 55
Stem density not limiting yield
Some yield reduction expected
Less than 39
Consider stand replacement
            Source: Undersander et al 2011, University of WI Extension publication A3620

While plant and stem counts are useful, to get a true determination of stand health, plants must be dug up so that crown and root tissue can be evaluated.  To do this you must split the crowns/roots.  The inside should be a creamy white color.  If it is yellowish brown to chocolate brown color the tissue is damaged or dying.  If more than 50% of the roots show these symptoms, reduce your stand counts and yield potential. 
            One other weather condition that can have a detrimental impact on alfalfa stands is freeze/thaw cycles. These cycles that typically occur in February through March often present the greatest danger of winter injury in Ohio. There is the potential during these cycles to physically lift or heave alfalfa plants out of the soil.  This heaving exposes the crown of the alfalfa plant making it more susceptible to temperature and physical injury.  In some cases, heaving breaks the root system, effectively killing the plant.  Heaving tends to be more of a problem in wet, saturated soils and clay soils.
            Although winter temperatures and snow cover amount are primary driving factors affecting alfalfa winter survival, there are also management factors that growers can control to decrease the chance of winter injury.  Those factors include:
·         Selecting varieties with good winter hardiness and disease resistance.
·         Maintaining soil fertility levels.  Potassium in particular is associated with enhancing alfalfa tolerance to winter injury.
·         Improving soil drainage.
·         Harvest management: more cuts is generally associated with a higher risk of winter injury, particularly if the last fall cut falls in that mid-September  to mid-October time frame.