The Cold Spell and Corn Crops
Wayne Fithian, Rob-See-Co Agronomy Manager
Every year there is a percentage of the corn crop that is exposed to very cold, wet conditions between planting and emergence. It is simply a consequence of farmers trying to plant their crop as early as they are able. Early planting is a great way to improve the chance of realizing the highest yield potential; research has shown this, farmers have learned this from personal experience, and seed company agronomists preach this - this one included! So, I think having a few fields challenged by cold temps is a good thing - it means our customers are trying hard to do the right things to raise a great crop!
Over the span of my career I have experienced two corn fields that were impacted negatively by exposure to freezing temperatures after imbibing enough water to start the germination process but before emergence - both involved really cold weather that dropped soil temps in the seed zone below 32 F, and both fields had to be replanted. Based on this, my interpretation is that actual kill by freezing temps is quite rare.
Over these same years, I have observed multiple fields someplace(s) every year where stand establishment was reduced by what we refer to as "chilling injury," and which is highly correlated to the rating in our characteristic chart called "Emergence."
Chilling injury occurs when soil temperatures in the seed zone drop into the low 40 F range (or lower, but still above freezing) just as the seed begins to imbibe water. Literally, the fields that were planted during the 24 to 48 hours immediately prior to the weather event will be the most impacted, because it is that initial drink of cold water, and not the chill after germination has begun, that causes the problem. A seed that has already germinated and begun to grow has a very high sugar content, and this sugar acts like an antifreeze and helps the germinated seedling endure the cold spell with much less impact compared to seed that has not yet begun to grow.
Will the chilling injury be severe enough to cause reduced stand? Perhaps - it depends on how long the cold spell lasts (and it looks like this one will be at least through the weekend, which is pretty long), how warm the soil was at planting (warmer is better because it reduces how quickly the soil cools), how deep the corn was planted (deeper is better because deeper is generally warmer), the soil texture (finer texture is better than more coarse, because the cold penetrates a coarse soil deeper and quicker), the quality of the seed (high saturated cold test is better), and the emergence characteristics of the specific hybrid(s) involved (higher scores mean a higher percent emerged plants).
We will assume the seed quality is great - or we shouldn't have it out there. So that means that the amount of stand loss will be dependent on the soil temp and type, the planting depth, and the emergence characteristics of the hybrid, and how cold it actually gets in the seed zone. Do you have a soil thermometer?