More fields than usual in Iowa are showing uneven growth of corn this year. Uneven corn can be caused by many factors, and there are usually multiple variables in play. Iowa State University Extension field agronomist Clarke McGrath put together the following list of reasons why farmers are seeing uneven spots in fields. Based at Harlan in western Iowa, McGrath covers west central and southwest Iowa.

1. Cold, wet soils early in the season. This situation limited early root formation, followed by dry (and hard) soils that aren’t as conducive to root growth.

2. Heavy residue areas. In some areas there seems to be more crop residue than normal this year, which lowers soil temperature and can keep soils cooler.

3. Compacted areas. This includes both sidewall soil compaction in the seed furrow and compaction right under the seminal root system, about 3 to 4 inches below. Some agronomists theorize that the lack of a good freeze/thaw cycle contributed to this. “We are even finding it in long-term, no-till fields, which likely means this isn’t something we did, but more a Mother Nature issue,” says McGrath.

4. NH₃ burn. Anhydrous ammonia was applied and the corn was planted too soon after the application.

5. Insect injury to crown and/or mesocotyl.

6. Early season seedling disease of mesocotyl and/or crown.

7. A few cases of herbicide injury/carryover.

8. Soil temperatures variations. Usually this is a result you see in lighter colored soils, wet areas, and/or heavier crop residue cover.

9. Tillage patterns. This can show up especially with any tillage done mid-spring after we started getting some moisture.

10. Extra soil washed in to the seed furrow. This occurs where trash whippers “trenched” a furrow in the row resulting in very deep planted corn (3 inches or more).

11. Loose, dry and “fluffy” soil in the seed zone. The soil settled with some of the early rains. This shallowed up some farmers’ planting depth by a ½ inch to 1 inch or more. That set them up for trying to grow nodal roots shallower than you’d like to see.

12. Some areas of fields where heavy rains washed soil out of the row. This resulted in very shallow (1 inch or less) planted corn and the corresponding dreaded “rootless corn syndrome.” This was especially bad in tilled fields and fields where trash whippers were run deeper into the soil.

13. Sidewall smearing/compaction. “I’ve seen quite a bit of this with some of our middle and later planting windows this year,” says McGrath.

There aren’t easy answers to explain the root cause (pun intended) of uneven corn this season, says McGrath. Unusual weather conditions, which started last winter and extended into this spring, and long periods of stress magnify small differences within fields and improve the odds of seedling disease, insect injury, chemical injury, etc. having an effect. Any of these factors can make the plant more susceptible to slow root growth and top growth of the plants.

Managing and preventing uneven corn, what can you do?

Small management changes like floating trash whippers, higher dose seed treatments, slower planting speeds, and straw choppers/spreaders on combines can help with some of these issues, he says. It’s always a good idea to look over the field as a whole for any patterns to the uneven corn that may help determine causes.

“Many of the stunted and uneven areas of fields can and probably will improve to a degree, especially if we can get some moisture in some of the areas where the upper soil profile could use it,” says McGrath. “I know, it sounds crazy to be talking about needing moisture after we fought an excess of it all spring in many areas, but while the subsoil is still full of moisture, in many areas the upper rooting zone is drying out. So, with limited root systems, stunted plants will continue to suffer more than the good parts of the field if we have extended dry weather. If we get moisture where we need it, things will likely look better…until tasseling time. Then the uneven growth and development of the field will show up again as compromised plants typically tassel later than the rest of the field.”

See U.S. Drought Monitor for current conditions

While it depends on the field, McGrath offers this general advice when it comes to taking management steps for uneven corn:

1. Uneven corn seems to be more prevalent in corn on corn again this year. Agronomists are asking if the rotation to a different type of root system, like tap-rooted soybeans, helped to offset this somewhat. Field observations are agreeing with this. The flip side is that crop rotation decisions are tough to base on one really odd winter freeze/thaw cycle. The grain markets aren’t helping us much with rotation decisions lately either, notes McGrath.

2. Some farmers are asking if they should do some sort of mid-level or deep-tillage to correct this. “What I have found has been so variable within fields that tillage may not address the issue as well as a ‘real’ Iowa winter,” says McGrath. “Hard to have a farmer run through a lot of acres burning diesel fuel, time and risking soil erosion for spotty and shallow, tight soil issues. Best strategy we can advise right now is to work with your agronomy or crop consultant team and make an area-by-area evaluation of this situation when you have a chance this fall.”

3. Since each case is different, the best idea would be to work with your local dealers and ISU agronomists. Based on their advice for your specific field situations, determine what management factors can help out in the future.

Related articles worth reading are Short Corn and Variable Growth and Tools to Calculate Yield Loss From Uneven Heights.