Is your Corn at Risk for Cold Injury?
Corn is a tropical plant. Just your reminder when you are frustrated that your corn has been sitting in the ground for 3 weeks in cool temps early in spring. Warm temps at the beginning of April resulted in a fair amount of corn getting planted this year. However, this cold spell has a lot of you wondering, what risks are we facing for the seed in the ground? There are two main risks we need to consider; imbibitional chilling and cold injury.
A lot of processes start happening the minute we put corn in the ground. For the first 48 hours after planting, a seed of corn will imbibe water. This is the process by which the dried out kernel rehydrates all its cells and gets ready for cellular growth. A seed will imbibe about 30% of its weight as water before germination can even happen. However, if this process happens during weather colder than 50 degrees, cells can rupture, and kernels and shoots will no longer be viable or at the least significantly damaged, particularly if the temperature changes dramatically during imbibition. If the temperatures stay above 50 for those first 48 hours and then drop below 50, seeds will be viable. Its that first 48 hours that are the most critical. If you planted within the last week, your seed may be at risk to imbibitional chilling injury.
Cold injury occurs when soil temperatures change after the process of imbibing water is complete. For example, if you planted on April 6th, soil temps remained above 50 degrees for 24 to 48 hours, meaning the seed was not at risk for imbibitional chilling. However, on the 10th of April, soil temps reached 44 degrees. These seeds are now at a risk for cold injury.
Some of you planted as early as March 28th and 29th, and those plantings were well past the imbibitional chilling window. Some of those seedlings sprouted at this point. Freezing temperatures can cause damage ranging from leaf injury to leaf tissue death. As long as the growing point is below ground (until V4 to V6) the plants, even if damaged, should recover. However, when we have consistently cold temperatures, the ground around the growing point also drops in temperature. If that soil an inch or so deep gets down to freezing or below, this can kill or damage the growing point.
Damage to pre-emerged seedlings
Prior to emergence, seedlings are very sensitive to freezing temperatures. If freezing temperatures occur around the coleoptile (the first shoot coming from the seed), the tissue may turn brown and rupture. If this occurs, chances of seedling survival are lower, as the coleoptile is no longer present to protect the first leaves as they push toward the soil surface. This often results in the first leaves leafing out underground and never making it to the surface. Alternatively, the coleoptile tip might not rupture, but the dying tissue will trap the first leaves, making it impossible for them to emerge. Generally, we see worse results when damage happens to the coleoptile below or at the soil surface than if the plant had been emerged. If the plant had been emerged, the leaf and leaf sheath can act as a buffer for the growing point.
A study by Pioneer placed temperature data loggers in a tilled field area and in high corn residue. Around 120 soil GDU’s are needed for corn emergence. During a 30 day timeframe during April, the tilled soil accumulated 99 soil GDU’s while the heavy residue covered soil only accumulated 28 soil GDU’s. Soils with heavy residue are slower to warm and may put seeds at a greater risk for cold injury. When planting, aggressive use of row cleaners can help maintain and increase soil temps for the seed bed.
So, What Can We Realistically Expect?
In most of our cases, we are likely to see just a slightly higher % stand loss. This will likely not be significant enough to do anything about. However, it is important that if you think you may have some fields at risk to watch them closely in the coming weeks. As emergence happens, take stand counts, dig for seeds not emerged, and document any unusual shoot growth like twisted or corkscrewed coleoptiles. Look for uniformity of emergence, both in spacing of emerged plants and plant height.
Check out the stress ratings on your planted hybrids. This rating tells you how good genetically a hybrid is at handling stresses. Some hybrids will do this better than others. While not a concern for this year, if planning some early April planting again, prioritize some of the higher stress rating hybrids for first planting in 2021.
As always, seed treatment can help keep your seed viable through long stretches before emergence. It’ll also help if protect the seed and seedling against any seedling diseases if the plant or seed is damaged from cold stress.
Questions on cold injury and what to look for? Get in touch! We’d love to talk you through it.