By Jason Kelley, Wheat and Feed Grains Agronomist
Some of you may be getting questions about yield potential of very late planted corn (Mid-to Late May). I am hearing that some producers still have some corn they intend to plant or replant over the next week or so provided field conditions allow for planting. I am also hearing of some producers who planted all of their intended corn acres and now are considering switching some soybean acres over to corn.
So what is the yield potential of corn planted in Mid-May or later? I think most realize at this point in May that yield potential is dropping every day. From our planting date studies that were conducted in past years, yields of irrigated corn start dropping in late April or early May depending on what part of the state you are located at. At Marianna, Arkansas, in an 8 year planting date study (2008-2015) corn planted prior to May 1 on average had 100% of maximum yield potential. Corn yields slowly declined each week when planting was delayed after May 1. Below are average % relative yields for each week in May at Marianna from planting date studies.
A field with a 200 bu/acre yield history in past years, when planted May 20thwould have an approximate 85% yield potential or roughly a 170 bu/acre potential, provided stands, irrigation management, disease management, etc are all adequate for optimum yields (BEST CASE SCENERIO).
In our corn research verification program we have a limited number of fields that have been planted in May (five fields). Planting dates and corresponding yields are shown below. These yields are from whole field averages and were produced following normal extension recommendations.
This data highlights that good yields can be realized on late plantings with proper management, but also highlights that yield variability can be seen. The importance of timely and proper irrigation and timeliness of inputs with late planted corn is very important to achieve maximum yield potential.
How does late planting impact corn growth and development?
In general corn develops at a much faster rate in late plantings than early planting due to rapid accumulation of heat units. Inputs such as herbicides and sidedress nitrogen will occur much quicker after planting compared to a typical March or April planting. Below is how late planted corn developed compared to earlier planting dates in a planting date study at Marianna, Arkansas with a wide range of planting dates. Keep in mind, heat unit accumulation will dictate how rapid corn growth is.
*Dates of harvest with corn at approximate 18% grain moisture. Days to harvest can vary greatly depending on drying conditions after maturity. Hybrid relative maturity will also have an impact on harvest date.
Hybrid maturity and selection: In past planting date studies, yields of hybrids with a relative maturity of 115-120 days tended to provide the greatest yields when planted late. Early maturing hybrids (<110 day) should be avoided as yields tend to be considerably less than full season hybrids. Keep in mind that September will be the drydown period for late planted corn instead of August. For those producers without bins or dryers, a hybrid with a maturity of 114-117 may be best as drydown in some years for full 120 day hybrid may be longer than desired. Drydown in September will likely be slower than what is typically seen in August. A harvest date for a 114 day maturity hybrid at 18% grain moisture compared to 120 day hybrid would likely be a week or more difference in harvest if field drying.
Another consideration is plant height and lodging resistance. Late planting will cause plants to become taller compared to early plantings and can increase lodging potential. Extremely tall hybrids or hybrids that are prone to lodging should be avoided.
Plant population: A recommended final plant population of approximately 32,000 plants/acre is still desired with late planting, however with late planting a higher percentage of plants may emerge, so the seeding rate may be able to be reduced slightly to still reach the desired population. Planting 36-38K seeds/acre may unnecessarily increase lodging potential later in the season.
Irrigation: Timely and proper irrigation is needed for successful late planted corn most years. Typically from past experiences, May planted corn often requires 1 or 2 more furrow irrigations or 2-3 pivot irrigations compared to a March-April planting.
Foliar Fungicide: Foliar diseases such as southern rust will more likely be a yield limiting factor in late planted corn. Typically early planted corn may “outrun” southern rust, but with corn maturity pushed back, the risk of southern rust being a yield reducer is real. Budget for a foliar fungicide application at tassel or early grain fill.