The optimum planting date varies by latitude in the United States. The majority of corn is grown in the Corn Belt and optimal planting ranges from April 15 in the southern Corn Belt to May 7 in the north. Planting dates are much earlier further south. Soil conditions with temperatures near 50°F are ideal for seed germination. Be aware of frost free dates in your region. Check with your insurance company to ensure that you have coverage when planting early.
Field corn can be planted too early. Imbibitional chilling, sub-lethal chilling, and frost can be problems when corn is planted too early. In general, research has shown that frost does not cause significant yield impacts even when leaf tissue is killed by frost two times or more. Less information is available regarding imbibitional chilling and sub-lethal chilling, but stand reductions have been observed with imbibitional chilling. Another issue is development of disease pathogens. Corn usually evades pathogens by growing and developing faster than the pathogen. Growth of corn is relatively slow at cool temperatures, while pathogen disease growth and development can be relatively greater and overcome the corn seedling.
Planter performance is important when planting corn. Corn sometimes emerges unevenly because of environmental conditions beyond the control of growers. However, timely planter servicing and adjustment, as well as appropriate management practices, can help prevent many stand uniformity problems. The following are some tips for improving the uniformity of seed placement during planting. 1.) Keep the planting speed within the range specified in the planter's manual. 2.) Match the seed grade with the planter plate. 3.) Check planters with finger pickups for wear on the back plate and brush (use a feeler gauge to check tension on the fingers, and then tighten them correctly). 4). Check for wear on double-disc openers and seed tubes. 5.) Make sure the sprocket settings on the planter transmission are correct. 6.) Check for worn chains, stiff chain links, and improper tire pressure. 7.) Make sure seed drop tubes are clean and clear of any obstructions. 8.) Clean seed tube sensors if a planter monitor is being used. 9.) Make sure coulters and disc openers are aligned. 10.) Match the air pressure to the weight of the seed being planted. 11.) Make planter adjustments and follow lubricant recommendations when using seed-applied insecticides (e.g. Poncho and Cruiser)
Field corn planting depth can vary. Current recommendations are to plant corn seed 1.5 to 2 inches deep. If planting conditions are dry, planting to moisture is often practiced to help with uniformity of emergence, but this may be affected by soil texture. In heavy soils, corn seed should not be planted deeper than 2.5 inches regardless of the conditions. In lighter sandy soils planting 3.0 inches deep may be necessary. Some states recommend planting shallower in no-till conditions. Planting shallower than 1.5 inches might affect corn growth and development with some herbicides like Prowl.
Research on plant spacing variation is mixed. Some recent research indicates that as plant spacing variation increases, grain yield decreases by one bushel per inch of standard deviation above two inches. Other research indicates that grain yield decreases at similar rates, but the critical threshold is above 5 inches. Stands that have that much deviation would obviously be noticed by growers and repair and maintenance of the planter would occur.
Seed-applied treatments, especially fungicides, are needed for corn. A number of pathogens will attack a germinating corn seed. Fusarium, Rhizoctonia, Helminthosporium, Penicillium and Aspergillus are typical examples of pathogens waiting to attack corn seed in the soil. In cool wet environments, Pythium can also be a problem and other fungicides may need to be applied to the seed. Seed insecticides are not as universally applied as fungicides, but they may be needed in certain management situations, i.e. rotating into pasture, alfalfa, etc.
Polymer coatings are temperature sensitive where polymer molecules change orientation as temperature increases, allowing water to enter the seed coat and begin the process of germination. The idea is that once soil temperature is at a critical level where seed germination can begin and growth can occur, the polymer allows water to cross the polymer. Most data indicates stands from polymer-coated seeds are not improved and that seedling emergence occurs over a longer period of time leading to variability which can ultimately decrease yield. So while the concept is attractive the real world results derived from research trials are not adequate.
For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
The following is the link to the corn extension specialists: state extension corn specialist