By Joel Ransom
Extension Agronomist for Cereal Crops
The recent warmer weather has been nearly ideal for corn development. Based on NDAWN maps, corn growing degree (GDDs) accumulations are running slightly ahead of the long term average for most of the state, with the some locations in the southeastern part of the state running 50 to 100 GDDs behind normal. The usefulness of using GDDs to estimate crop development is borne out by recent USDA Crop Progress Report that reports corn silking, at 54 percent, nearly identical to the average of 53 percent.
The reason that GDDs are more useful than calendar days in predicting corn growth stage is that there is little effect of day length on corn development (like in soybean) and the physiological processes that drive growth are highly temperature dependent. Nevertheless since we live by calendar days some “translation” between GDDs and calendar days can be useful. I will use an 85 relative maturity hybrid grown near Fargo as an example. This hybrid takes about 1075 GDDs to begin silking and 2040 GDDs to reach physiological maturity. In a typical year for corn planted on May 1st this means corn will silk on July 17th (80 days to silking), and reach maturity on September 14th (~137 days to maturity). This year we are only a couple of days behind the predicted long term silking date suggesting that if we continue to get normal weather we are or less on track to reach maturity in by the third week in September. This will position the corn crop in a favorable environment to dry down before the really cold weather sets in, as we still have reasonably warm weather in late September and early October to facility field drying. Of course time will tell if we will have normal weather for the rest of the season. In addition to using NDAWN to monitor GDD accumulations, I think you will find the Corn GDD U2U Decision Support Tool at https://mygeohub.org/groups/u2u/gdd useful, particularly for predicting maturity dates and probabilities surrounding those predicted dates.
In addition to temperature, moisture is key to corn development. Because of the long-season growth of corn, it is a heavy water user. During a hot dry day, a fully canopied corn crop can transpire more than a third of an inch of water. Except for a few locations, most notably the northwestern part of the state, rainfall for the season has been above average. Nevertheless the recent rainfall that has fallen over most of the state was extremely timely. Water deficits are significant for the western third of the state and stored soil moisture is nearly depleted. Heavier textured soils can retain up to 10 inches of water that can be access by the corn plant the root system is well developed (see following table). As moisture deficits intensify, the leaves of corn plants curl during the heat of the day. This is often followed by leaf firing if drought persist. Corn is most sensitive to drought stress from silking through the blister stage. Western North Dakota are in need of some additional rains for the next couple of weeks to ensure that yields are not significantly compromised. For the moment, soil moisture does not appear to be a constraining factor in the eastern third of the state for corn development.
