Ohio State University Extension
Department of Horticulture and Crop Science
2021 Coffey Road, Columbus, Ohio 43210-1044

Assessing Effects of Uneven Emergence on Corn Yields

AGF-122-90

A key step in optimize corn grain production is uniform kernel germination and seedling emergence. However, it is not unusual to find varying degrees of delayed emergence in corn fields throughout the state every year. Uneven emergence affects crop performance because competition from larger, early emerging plants decreases the yield from smaller, later emerging plants. The primary causes of delayed seedling emergence in corn include 1) soil moisture variability within the seed depth zone, 2) poor seed to soil contact due to cloddy soils, 3) inability of no-till coulters to slice cleanly through surface residues, 4) worn disc openers, and 5) misadjusted closing wheels. Other causes include soil temperature variability within the seed zone, soil crusting prior to emergence, occurrence of certain types of herbicide injury, and variable insect and/or soil-borne disease pressure.

The following are some of the most commonly asked questions concerning poor stand related to uneven emergence.

Should You Replant Stands With Uneven Emergence?

• If unevenness is mostly row-to-row, replanting will probably not increase yield.
• If the delay in emergence is less than 2 weeks, replanting will increase yields less than 5%, regardless of the pattern of unevenness.
• If 1/2 or more of the plants in the stand emerge 3 weeks late or later, then replanting may increase yields up to 10%. To decide whether to replant in this situation, estimate both the expected economic return of the increased yield compared to your replanting costs and the risk of emergence problems with the replanted stand.

Should You Fill In A Poor Stand?

When replanting a poor stand (3/4 stand loss or greater), you can either tear up the stand and replant the whole field, or fill in the existing stand and create uneven emergence.

• If you replant within 2 weeks of planting the original stand, filling in the existing stand may be an option. Yields will be similar to those from a uniform-emerging, replanted stand, if you can get relatively uniform plant spacing within the row between old and new plants. However, within two weeks of planting, it may be too early to determine what the final stand will be.
• If you replant 3 weeks after the initial planting, yield potential is about 10% greater if you tear up the field and start over with an even-emerging stand. Balance this possible yield increase against the additional cost of tillage, seed, pesticide and dryer fuel.

Should You Protect Late-Emerging Plants During Row Cultivation?

• If late-emerging plants are within 1 1/2 to 2 weeks of those emerging early, avoid burying them during cultivation.
• Protect plants emerging 3 weeks late if 1/2 or more of the plants in the stand are late-emergers.
• If less than 1/4 of the stand is emerging 3 weeks later or later, it probably won't pay to encourage their survival. Yields will be about the same whether or not these delayed plants are buried.

Consult North Central Regional Extension Publication No. 344, "Uneven Emergence in Corn," for a comprehensive discussion of why corn emerges unevenly, research conducted to assess effects on hybrid yield reduction, management options available for dealing with uneven emerging stands, and suggestions for obtaining uniform emergence.

Prepared by:
Peter R. Thomison
Extension Agronomist