Sometimes when I say the word “physiology” in a sentence, I suddenly see this distant gaze in a person’s eyes. Physiology, growth, development, enzymes, tissue are words that are not commonly used in a conversation unless you are talking about biology or some related science. On Mar. 13th, Georgia experienced below freezing temperatures ranging from 220 F in mid-Georgia to 270 F in south Georgia. I am limiting the scope of the area only because of the subject matter. Usually in early March, Georgia growers will have sweet corn, a little field corn, some vegetables and fruits that would be vulnerable to such a drop in temperature.
For the purpose of this article, I am focusing my attention to field corn and some sweet corn. In the last twelve days, after talking with county Extension agents, consultants and growers, some sweet corn stands were completely lost. Others lost an enough percentage of plants to warrant replanting. Field corn damage, on the other hand, was limited to killing most of the above ground tissue only. Fortunately, most growers began to see new life emerge from underground within 48 hours and can now see one to two new leaves. Now you say, Dewey what is your point? My point is that it’s important to recognize how many leaves were exposed at the time of the freeze. There have been enough growing degree units accumulated since then for roughly 1.5 leaves to emerge and make your stand look promising. This is why it is good to remember your plant physiology.
The initial two or three leaves that may have been exposed were killed and only a remnant of the collar, or sheath, will remain. Instead of seeing a plant with one to town developed leaves, you must look for the tissue of the dead leaves to properly account for the true age. Please understand, I am not nic-picking. I just don’t want you to miss the opportunity to have the best impact and return on your investments. I have always encouraged nitrogen applications and weed control by the physiological development of both corn and weeds.
Dr. Eric Prostko, UGA Weed Scientist, will tell you that there is a good window for effective weed control in corn from the V-3 to V-5 stage. I always say that early N applications need to begin at that same phase of growth since the plant has exhausted all the energy of the seed. It is easy to forget that a damaged plant is at V3 to V5 growth stage when you may only see the leaves that were not damaged and have grown since the freeze. Depending on the amount of nitrogen and sulfur you may have applied before or at planting, it can be very critical (particularly on sandy soils) to make sure you hit that best window of impact. The initiation of the embryonic ears begins during this rapid growth period. I wouldn’t want you to get behind because you didn’t get visual cues from leaf growth.
I encourage all corn growers to use the growing degree calculator on the University of Georgia Weather Network website (http://www.georgiaweather.net/) and keep track of the growing degree accumulations from the day you plant or the day corn emerges in your fields. As you manage your inputs, record the GDD’s of each application or activity that affects the plant so you can repeat success the next year. The plant is responding to the environment and not the calendar day. In the early stages of corn growth, a new leaf will appear with every additional 84 growing degree units on average. Growers who us this method are better able to anticipate the timely application of inputs to get the best return on the investment.
The season so far in 2022 has been cooler in the mid weeks of March than it was in 2021 and 2020. Nighttime temperatures have been cooler and growing degree day accumulations smaller so corn growth has been slower than the previous two years. We still have a good bit of time to get the 2022 corn in the ground in south to mid Georgia to have a great opportunity to produce an excellent crop. Growers in north Georgia are well placed to take advantage of good moisture when temperatures warm.