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Evaluating this Year’s Corn Stand

Source: Dave Nicolai, Extension Educator, Crops, UMN Extension

Cool and cloudy conditions across much of Minnesota prevented fields from drying out much during the week ending May 28, 2017, which limited farmers to 2.8 days suitable for fieldwork according to USDA’s National Agricultural Statistics Service. Corn planting in Minnesota is nearing completion, with 96 percent of the acreage planted. Eighty-one percent of the corn crop had emerged, 5 days behind last year, but 3 days ahead of the five-year average. Soybean planting was 81 percent complete, 8 days behind last year, but 3 days ahead of average. Thirty-nine percent of the soybean acreage had emerged, 5 days behind last year. Small grain planting was wrapping up throughout the State. Spring wheat was 97 percent emerged, with 16 percent at or beyond the jointing stage.

Evaluating Corn Early Season Corn Populations
Many farmers now take the time to walk and scout their early planted corn for emergence problems, plant populations, weed, disease and insect levels. One of the first criteria in this early season scouting is to assess the field’s plant populations. To determine the number of plants in an acre (plant density) count the plants in a row length that is equal to 1/1000 of an acre. This row length will vary depending on the width of the rows (30 inch rows = 17 feet 5 inches or for 22 inch rows = 23 feet 10 inches). To get a reliable average, sample 15 to 20 representative areas per 40 acres. Once the average number of plants per 1/1000 of an acre is determined, multiply by 1000 to calculate the number of plants per acre.

Optimal corn planting rates vary somewhat with hybrid, soil productivity, and expected yield. However, planting rates of 34,000 to 36,000 seeds per acre generally maximize economic return in most fields in Minnesota based on University of Minnesota research. A final stand that is 5 percent less than the planting rate is common, but can vary somewhat based on a variety of factors. Planting too many seeds generally does not reduce corn yield, but it can reduce economic return.

Assess the Unevenness of Stands
Some factors that cause corn plant variability:

  1. Planter speed especially for planters that are not classified as “High Speed” which can operate at 7 to 10 mph versus a conventional planter operating at a 5 mph speed.
  2. No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
  3. Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.
  4. Frost
  5. Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
  6. Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.
  7. Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
  8. Inter-plant competition for solar radiation, water and nutrients
  9. Low soil fertility
  10. Saturated and/or cool soils: May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.
  11. Drought

Note patterns of poor emergence. At times, they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing.

Don't forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential can be reduced.


David Nicolai
Extension Educator, Crops & Institute for Ag Prof Coord
(651) 480-7706
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