Before I get into the thick of what I mean by not getting behind, I need to give a snap shot of our current conditions. Corn planting across the state is moving at a very fast pace where we have had good sunshine. Many growers in southwest Georgia have finished or close to finishing. As you move closer to middle Georgia and also eastward, rains have delayed planting a little longer. Fields have been very wet and many growers are working around low spots. I’ve reached out to growers in the area and most are half way or more to finishing. The upper coastal plains area is similar in that some fields with heavier soil types are slower to dry. Rainfall early this week in north Georgia has delayed ground work. The further you move northward on in to the Piedmont and Limestone Valley/Mountain areas, growers are having a difficult time getting ground prepared.
Now to my main point of this entry. Yesterday, I checked growing degree day units (GDU) around south-Georgia and was surprised to see that GDU accumulation was faster than I expected. This means that corn is growing much faster than the last three to four years. It is important to recognize this because we can easily get behind the growth curve if we are not paying attention. I also had a great discussion with Dr. Corey Bryant, UGA’s Corn, Soybean and Small Grain agronomist regarding the dangers in getting behind in corn management. He agreed that it is important to be proactive as possible. In fact, he mentioned that some of Georgia’s ag suppliers are having trouble with getting much needed products. So there is reason for urgency.
In our current case, corn in fields planted in the later portion of the first week of March in south-Georgia are approaching the V3 stage. Our most effective and efficient weed control is generally between V3 and V4 phase of growth simply because weeds are just emerging or in a very vulnerable stage of growth. Also, the corn plant is rapidly exploring the top 6 to 8 inches of top soil and may need additional care in water or nutrients depending on what is currently available.
A lot of growers in south-southwest Georgia began planting near March 8-10th. The following table of accumulated GDUs is a snap shot of several weather stations across the southern areas assuming a March 9th planting date to yesterday’s (March 25th) GDU accumulation. Remember it takes about 100 to 110 GDU’s for corn to emerge.
GDU accumulations between March 9th and March 24, 2020 is over twice the average of the last three years. In fact, it is very similar to what we saw in 2012. The 2012 corn season was very warm and drier than normal. It was very tough on dryland corn but great for irrigated corn. Irrigated corn growers harvested some of their best corn yields that year. Corn growth moved extremely fast that year.
How do I derive that we are at or near V3 corn in these areas? If we look at the average GDU accumulation from the table for all locations (excluding Dawson, Tifton, Baxley, and Statesboro), then we get 338 GDU’s. Subtracting 100 to 110 GDU’s for emergence, we have 228 to 238 gdu’s. Divide that by 84 GDU’s for each leaf and we derive 2.7 to 2.8 leaves. I needed some ground “truthing” so I called Rome Ethredge in Donaldsonville and he was kind enough to confirm that he was seeing 2 to 2.5 leaves. He also was surprised by the rapid accumulation of GDU’s and confirm that he was beginning to see weeds emergence such as morningglories. Rome sent this picture of one of his grower’s corn field.
During this early growth period, corn plants add a leaf every 84 GDU’s. At the current GDU accumulation (35+ hours per day), corn will add a leaf every 2.4 days. Please plan according. Corn will begin transitioning from vegetative state to a reproductive state between the V5 stage and V6 stage. Some scientist say as early as the V4 stage.
Let’s make sure we don’t get behind. Check fields for early weed emergence and preplan your postemergence spray program. Check your fertilizer plans and prepare to start sidedressing very soon. The tassel and ear development will be in full motion by V6/V7 stage. Walk fields to make sure there are no problems that may cause stress as your corn crop develops and move towards the early reproductive phase.
Here’s how to check and ground truth your field. Go to Georgiaweather.net. Look at the top banner. You will see Home, Maps and Summary, Crop Weather, Drought, Calculator, Background info, etc. Move your cursor to Calculator and drop down to degree day. In the Degree Day Calculator, choose the nearest weather station. In the box below the station is where you put your planting date and year. The box below is for the latest date (which would be yesterday’s data). In the base temperature, choose 50 and disregard (in the next box) temps above 86. Click on US and then calculate. The information will come up for 2020 and the previous three years. Remember to subtract ~ 100 to 110 GDU’s for emergence and then divide the rest by 84 to get approx. leaf stage. Adjust to what you see in the fields. Lot of things will cause little differences but it puts you in the ball park.