Early corn already rising
By ADAM SHEPARD
As we counted down the final days of April last month, our spring progress is variable depending on your location in the county. We seem to be in the pattern of just enough dry days to think about doing some field work then again come the showers. A couple of growers found conditions favorable to get some early corn planted before this pattern of wet weather hit.
Some corn planted on April 6, near New Holland is just now starting to spike through the cool wet soil. This brings up the conversation of growing degree days (GDD) or heat units needed to germination the corn and push it out of the soil. While advancements have been made in hybrid quality and traits the method in which we calculate the GDD’s for the corn remains the same. Past research from numerous sources indicates that corn growth nearly stops at temperatures above 86oF and temperatures below 50oF.
With those figures in mind the formula we use to calculate GDD’s is the 86/50 cutoff method. In order to determine the number of GDD’s we have accumulated on a given day we need the two following values: the maximum and minimum temperature for the day in question. Once we have those temperatures we look to make sure the maximum temp is at or below the 86oF mark and that the minimum temperature is at or above the 50oF mark. If the temperatures are above 86oF or below 50oF we simply use 86oF for the high and 50oF for the low.
So now that we have the formula to calculate GDD’s, why would we want to? Utilizing specific hybrid information provided by your seed company or the GDD accumulation chart in the Ohio State University Agronomy Guide we can determine when our corn will reach specific growth stages. For example the situation that some growers are experiencing right now is reaching the number of GDD’s to get the corn crop to germinate and emerge. Looking at the chart in the Agronomy Guide we know that it takes roughly 100 GDD’s to get a corn crop to emerge. So if we can look back from the date of planting and research the daily max and min temps that we have encountered since planting the grower can calculate to see roughly how many GDD’s have been accumulated and estimate when he/she could expect to see emergence.
Another example GDD’s could be helpful is during time sensitive applications of herbicide or fungicide. Specifically the calculation of GDD’s to determine tassel of the corn field can be very helpful to schedule the airplane for optimum timing on fungicide application at tassel. Often times when we determine that the corn field has reached the tassel timing recommended for application the airplane is at least one or two days out. By the time the plane is available the optimum window for application may be closing or passed. If we can use GDD’s and weather forecasting to determine three or four days in advance of tassel to schedule the airplane we could get better results out of our application.
Weather information for your area including specific daily max and min temps can be found on the National Weather Service website www.weather.gov and type in your zip code. If you are located near one of the OSU OARDC locations the GDD accumulation is located on the OARDC website at http://www.oardc.ohio-state.edu/newweather/.
(Adam Shepard is Ohio State University Extension education specialist for Fayette County.)