Dave Wilson, Research Agronomist
Now that the snow is gone across ‘certain areas’ of PA and to the south, we are able to see the winter annual small grain forages and do some evaluations. I have been getting calls with questions concerning freeze- injury and potential winterkill of the winter annual small grain forages.
Most winterkill occurs during this time of year (late winter into early spring). Winter annual small grains are most winter hardy earlier (during December and January). Winter hardiness is lost more quickly in years when we have alternate freezing and thawing periods, or a mid-winter thaw. Plants that break dormancy during winter lose some of their winter hardiness each time that occurs. Spring freeze injury is the greatest when the small grain breaks dormancy and starts to grow, then is hit with a spell of freezing temperatures.
As we begin to get warming trends, this will cause plants begin to lose their winter hardiness, which makes them more vulnerable to later cold snaps.
In areas that were snow covered and remain snow covered, the snow insulates the plants, soil and the crowns below the soil to prevent both the effects of early warming trends and subsequent cold blasts.
Exposed fields with no snow cover are more vulnerable to freeze injury and winterkill without that buffer. Small grains in fields with no snow cover that were exposed to prolonged temperatures of -10°F or lower have a much higher risk of winterkill. We had reports from various dairy farms of water lines freezing that were even buried 3 ft. deep, so we know this years’ extended sub- freezing cold spell may have permeated down into subsurface roots zones which could have done some root damage in certain areas.
In certain years we can get injury occurring across a large portion of our fields, but usually we see the most severe damage in low lying areas of the field or in areas that the cold air will settle and be held.
Freeze injury, also referred to as “burning” of the exposed leaves, will appear yellowing or browning the tips of the leaves, but this typically has little effect on small grain yield. The small grains often grow out of this early enough to flourish in the spring, with new green leaf growth that is also for adequate forage production. During mild winters, the leaves will stay green and have little freeze injury damage.
Barley is the most vulnerable winter annual small grain to suffer winter damage, generally followed by wheat and spelt at a similar hardiness level. Triticale varieties are usually slightly more winter hardy than the wheat, and rye is the most winter hardy. There may be some overlap and differences in these comparisons, depending on the particular varieties.
What we need to evaluate is the crown and the growing point of the plant, which should be somewhat protected by the soil cover, with the growing point an inch to an inch and a half below the soil surface. Winterkill is caused by direct freezing or damage to the crown and growing point. Plants growing from shallow planted seeds will be more vulnerable to winterkill, as well as plants that have been frost heaved up out of the soil, since their growing points may have been exposed.
Look for winter kill on low lying areas or poorly drained soils first, or where poor fall root growth may have occurred.
If the winter annual small grain has enough time to grow and be exposed to cooler temperatures in the fall and early winter before it goes dormant, then it goes through the process of “hardening” and this process impacts its winter hardiness. With adequate exposure to complete the hardening process, the crowns can withstand temperatures ranging from about -8°F to -12°F.
Plants that go through a hardening process with gradually cooling days for a longer period of time are usually more winter hardy than plants that are grown in years that temperatures plummet rapidly in the late fall into early winter.
Ice sheeting on exposed plants is very detrimental because the ice will suffocate the plant. Also, plants exposed directly to subfreezing temperatures and high winds will be subject to desiccation or drying out of the plant tissue.
Freeze injury will kill back leaves but not kill the plant, but freezing injury of the growing point can severely injury or kill the plant.
If we suspect winterkill, we can dig out some plants and look at the crown and examine the sub-soil growing point. This should appear nice and white in color and be firm from the combination of moisture and live tissue. If it has been damaged or killed by freezing, then it will be brown and wilted.
Variety types that start their spring growth earlier (at lower temperatures) and possibly earlier maturing varieties may be more vulnerable to winterkill if they start an earlier growth initiation in early spring and then are met with a freezing cold spell afterwards. Once spring growth starts at green up then the winter hardiness of the plant decreases quickly, which makes it vulnerable to winterkill if a cold front with freezing temperatures occurs.
Late planted small grains that didn’t have enough time to produce a strong crown system will be more vulnerable to winter damage, including frost heaving. If the small grain plant has at least two tillers and a well-developed crown root system that has been protected by the soil, then winter kill is less probable. Also very early planted small grains that have had excessive growth in the fall (9 to 11 inches) going into the winter will have an increased susceptibility to snow mold or winterkill, because the more advanced growth stages of small grains are more vulnerable to winter-kill in late winter or early spring.
It’s not uncommon that kill across a field will be non-uniform and sort of patchy, just localized in certain areas, especially if the field topography and soil moisture changes.
With an early evaluation we can get some read on the winterkill percentage in our fields, but it is advisable to wait until the plants break dormancy and watch as the fields begin to green up before considering replanting.
Well-developed crowns are typically more dense andwinter hardy than extended deeper roots, so in some case we may have both some above ground freeze injury to leaves, and depending on the soil depth of the frost line, winter damage to the smaller roots as well. If this is the case then the growing point of the crown has to grow both leaves and roots, and this can be very slow. As long as the crown and growing point was not killed, growth will indeed be delayed but will likely be a better option than having to reseed another crop.