Cold Damage on Winter Annuals

 By Jeremy Kichler

Below are a few words from Dr. Lisa Baxter on the winter annual forage situation.

The prolonged cold weather during the Christmas holiday has a lot of producers asking, “Are my winter annuals going to regrow?”

Unfortunately, there isn’t a clear answer that we can offer to this question. Many cool season forages can handle subfreezing temps for short periods and the degree of damage depends on air temperature, soil temperature, topography, winter precipitation, stand health, stand age, and stage of growth. Potential for recovery will depend on how much growth and what stage the plant was at before the cold snap. More advanced growth stages will be less susceptible to winter kill compared to tender young growth. Unfortunately, many producers planted late last fall because of late season drought so the plants may not be at the same stage of growth as in a “normal” year. Cold tolerance will even depend on temperature and variety in many cases. Oats are generally less winter hardy than other small grains and can suffer substantial yield loss when temperatures dip below 20°F. Ryegrass is likely intermediate to oats and other small grains in terms of winter hardiness, but there is a wide range within varieties.

So, what happens to the plant during a cold snap?

When forages experience subfreezing temperatures, the plant cells can break or rupture which contributes to the darker color leaves you may be finding. Grasses can be more tolerant to this than legumes and this would be why many winter annual weeds (usually broadleaf) seem to be more affected than the grasses growing around them. Cell death can occur when ice forms within the plant cells. This is why so many Extension agents are receiving pictures of brown grass this week!

The impact of freezing weather on forage quality is mixed and highly variable. The damaged forage may have a lower quality than what you were anticipating. Watch your cows closely for loss of condition and supplement their diet as needed to accommodate this difference.

So, what should you do?

The best way to combat cold damage is prevention. Plants need good leaf area during the fall to synthesize carbohydrates and accumulate organic reserves before winter. High K:N ratios in soil will help ensure winter hardiness as well.

Once temperatures warm back up, growth of the forages will be slow. Optimum temperatures for winter annual forages are typically between 60-80°F. The forages will grow much more slowly outside of the temperature range, so you may not be seeing regrowth yet if the

temperatures have remained below this range. Be careful grazing the vulnerable plant material. Graze carefully and give the plants time to rest.

Prussic acid shouldn’t be a concern unless you have old sorghums (including johnsongrass) hanging around the farm. If this is the case, delay grazing for at least 14 days to allow the compounds to dissipate.

Potential cold damage to tall fescue (from UK Master Grazer Website)

Damaging frosts significantly reduce forage quality in most forage species. Tall fescue is unique because it has waxy layer which lessens the damage caused by colder temperatures and forage quality remains high in comparison to other species. The quality loss from leaf deterioration is lower compared to other cool-season forages. Another unique attribute of tall fescue is that after experiencing a freeze, sugar content increases. This makes tall fescue ideal for stockpiling and winter grazing use.