COLUMBUS – Uneven plant spacing and emergence may cause significant yield losses in corn. Seed should be spaced as uniformly as possible within the row to ensure maximum yields and optimal crop performance.
Gaps. Corn plants next to a gap in the row may produce a larger ear or additional ears (if the hybrid has a prolific tendency), compensating to some extent for missing plants.
Skips can reduce yield in fields where the intended population is at or below the optimum, while doubles increase yield when populations are less than optimum.
Reduced plant stands will yield better if plants are spaced uniformly than if there are large gaps in the row.
As a rule of thumb, yields are reduced an additional 5 percent if there are gaps of 4 feet to 6 feet in the row and an additional 2 percent for gaps of 1 foot to 3 feet.
Uneven corn emergence generally has a greater impact on grain yield than uneven plant spacing.
Competition. Uneven emergence affects corn performance because competition from larger, early-emerging plants decreases the yield from smaller, later-emerging plants.
If the delay in emergence is less than two weeks, replanting increases yields less than 5 percent, regardless of the pattern of unevenness.
However, if one-half or more of the plants in the stand emerge three weeks late or later, then replanting may increase yields up to 10 percent.
Emergence delays of 10 days or more usually translate to growth stage differences of two leaves or more.
When two plants differ by two leaves or more, the younger, smaller plant is more likely to be barren or produce nubbin ears.
Weeds also tend to be a greater problem in those areas of a field characterized by skips and gaps in the corn rows, and slow, erratic corn emergence.
Environment. 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.
Most of the corn seed that will be planted in Ohio in 2007 is treated with seed-applied insecticides (e.g.. Poncho and Cruiser).
While these seed insecticides can help reduce stand losses from soil insects, it is critical that corn growers make planter adjustments and follow lubricant recommendations when using these seed-applied insecticides.
Unless these precautions are followed, the extra chemical loading on the seed may adversely affect the “plantability” of seed.
Vacuum planters may underseed and finger pickup planters may overseed. To improve planter accuracy, talc or graphite should be used according to the planter manufacturer’s recommendations.
With vacuum planters, it will probably be necessary to raise the vacuum to achieve more accurate seed drop.
Tip sheet. For more information on planter adjustments to improve stand establishment in corn, consult: Tips to Reduce Planter Performance Effects on Corn Yield, OSU Extension Fact Sheet AGF-150-01.
(Greg LaBarge is a Fulton County Ag educator and Peter Thomison is an OSU Extension Corn Production state specialist.)
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