Frost

Here is some good information concerning the recent frost as we begin to start evaluating soybeans and corn.  Below is information concerning alfalfa sent to me from Agronomist Randy Welch, Sr. Alfalfa and Forage Agronomist with Winfield Solutions, out of Wisconsin and Minnisota.

Parts of Ohio were hit with frost recently. The following article from Bob Nielsen at Purdue is very good at explaining the process of determining damage. In any case, the bottom line on diagnosing the severity of frost or low temperature injury to corn or soybean is that you generally need to wait three to five days after the weather event before you can accurately assess the extent of damage or recovery. Recognize that cool days following a frost event may slow the plants’ recovery and delay your ability to assess their health.

We must also consider the difference between a light frost and lethal cold temperatures. A light frost generally occurs at temperatures warmer than 28 degrees F. Lethal cold temperatures are those at or below 28 degrees.

Corn: A light frost prior to the 5 leaf stage will generally not kill a plant entirely. The above ground parts will likely be damaged but the plant will recover. Lethal temperatures for a period of time (a moving target but usually a few hours) can kill a plant even prior to the 5 leaf stage. The growing point may be below the ground but the plant actually freezes to that level.

Soybeans: If we maintain a live “axillary bud” following a frost or freeze event the plant will survive. Axillary buds develop at each leaf axil of the plant and can take over as the growing point (primary bud at the top of the plant) if forced to. If the plant is dead below the cotyledons start doing stand counts.

Alfalfa

New seedings: Damage to new seedings has been minimal due to their excellent frost tolerance. To determine if damage has occurred examine plants - they will first appear to wilt and then die over the next 3 to 5 days. If plants die back to the ground, the plant is dead. At least one set of leaves must have escaped damage for recovery to be expected. Determine the number of living plants per square foot. If more than 20 plants per square foot remain, stand will survive in good shape. As stands are thinner than 15 plants per square foot consider top seeding alfalfa.


Established stands: Evaluate the stands to determine 1) if less than 30 % stem tops are damaged, 2) if most or all stem tops are damaged, and 3) if the stems are frozen back to the ground. Damaged means wilting (usually visible in about 24 hours after frost) or yellow to brown discoloration (usually visible 3 to 5 days after the frost).


1) If less than 30% of stem tops show wilting/browning from frost, do nothing. Enough stems remain to provide good growth and yield of first cutting. Stand will have some yield reduction of first cutting but will recover completely on second cutting.


2) If most or all stem tops are damaged and stand is less than 10 inches tall, do nothing. The growing points have been killed but the alfalfa will form new buds at lower leaf junctures (axillary buds) and continue growing (first cutting might be delayed). Alfalfa may demonstrate some horizontal growth. Mowing existing top growth will not enhance recovery. If stand is over 12 inches tall, harvest and allow to regrow. None of the alfalfa that was frozen in the Midwest was over 12 inches when frosted to our knowledge. Note that frozen material may be high in nitrate.


3) If all stems on a plant are frozen back to the ground, the plant in dead. This extent of frost damage has not occurred in the Midwest to our knowledge. However, if observed and fewer than 5 plants per square foot remain, consider rotating to another crop and replanting alfalfa in another field to avoid autotoxicity.

Thanks and give a call if you need anything!

Auggie