All Is Not Lost Yet; Still Time to Plant Before Large Yield Penalties

May 10, 2024 4:30 PM
Blog Post

Planting progress started off strong, but recent rain events across the state have brought it to a screeching halt. It seems like fields get just about fit to get back in them to plant and it rains again. According to the May 6th USDA Crop Progress Report, corn planting was at 47% complete and soybeans at 30% complete, which is 2 days behind both last year and the 5-year average.

With more rain chances in the weather forecast, what does this mean for acres left to be planted?

We are still within our ideal planting window for both corn and soybeans. The decline in potential yield related to late planting dates begins after May 18 for corn, with a more rapid decline after June 1. For soybean, yield potential starts to decline after May 20. There is some variance between northern and southern Iowa. After May 20, yield losses from late planting are much higher for corn compared to soybean. However, soybean yield loss is also occurring. While there is still time, it is slipping away quickly with each additional rain delay.

Corn and soybean relative yield response to planting date.

We are still early enough yet that we wouldn’t consider needing to change maturities yet for corn or soybean. For corn, that discussion begins after May 31 and for soybeans June 30 (or at all). Remember while changing seed maturities can ensure avoiding fall frost, it also means you may not have corn hybrids or soybean varieties that are well adapted for Iowa soil conditions or disease pathogens. Additionally, a 60-day delay in planting only changes soybean maturity by 10 days in the fall.

While planting date is important, uniform seed emergence is also critical for high yield potential. Avoid the urge to start planting too early. Planting when soil conditions are marginally acceptable leads to sidewall compaction and wheel track compaction which will have season-long implications. Field cultivation, vertical tillage, and rotary hoeing to ‘dry out’ the soil may help in the short term, however, with continued rains could lead to crusting. Planting conditions and planter setup are key to ensuring adequate stand establishment and uniformity. When we can get back to planting, take time to make the needed adjustments with your planter as this plays a big role with stand establishment and uniformity. 

Additional Resources

Important Crop Insurance Dates

Ponding impacts on corn growth and development

Ponding impacts on soybean growth and development



Rebecca Vittetoe Field Agronomist in EC Iowa

Rebecca Vittetoe is an extension field agronomist in east central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, soybeans, and...

Mark Licht Associate Professor

Dr. Mark Licht is an associate professor and extension cropping systems specialist with Iowa State University Extension and Outreach. His extension, research and teaching program is focused on how to holistically manage Iowa cropping systems to achieve productivity, profitability and en...