NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

May 20, 1999

Decision to Replant Can be Difficult

Unexpected stand losses from flooding, late spring frosts, hail, insect or disease damage, herbicide or fertilizer injury or other causes can put corn and soybean producers in the position of evaluating the crop for possible replanting. Denise McWilliams, extension crop production specialist for North Dakota State University and the University of Minnesota, says growers should assess the need to replant carefully and not make a quick or uninformed decision.

Especially with low crop prices making it important to hold production costs down, careful consideration of the replant decision is essential, she says.

Growers faced with a thin stand should first scout the field thoroughly to determine the plant population and compare the actual stand to the desired population. Requirements of a crop insurance plan may be a consideration for replanting. Another major point, says McWilliams, is to compare the original planting date to the likely replanting date.

"Besides considering crop losses from a planting made at a later date, add in the cost of the replant seed and other replanting and pest control costs," McWilliams says. "This information, along with yield loss or gain from a later planting, can be used to determine if replanting is worth the time, money and effort."

Estimating plant population involves counting the number of viable plants in a length of row that equals 1/1000 of an acre in several spots across the field—six to eight spots across every 20 acres is a good sample. Length of row needed to equal 1/1000 acre varies with planting width. In 22-inch rows the length will be 23.8 feet; in 36-inch rows it is 14.5 feet. Average these counts and multiply by 1000 to get the plant population.

Actual stand counts will give a good estimate of plant population. Guessing at the population remaining in the field is more difficult, but the National Crop Insurance Service corn loss instruction book shows that a 75-percent stand will result in a 10-percent yield loss, a 50-percent stand in 26-percent loss, and a 25-percent stand in a 43-percent yield loss. Yield losses may increase with uneven distribution or large gaps or skips in the stand.

Actual stand counts are important in soybeans, as guessing at the remaining population is even more difficult, McWilliams says. Length of row to equal 1/1000 of an acre goes from 87 feet in 6-inch rows, to 52.3 feet in 10-inch rows, and 16.3 feet in 32-inch rows. Yield loss in soybeans may increase if seedlings are unevenly distributed.

After determining the plant population, the next step is to compare that population to the target population of the original planting and determine the cost of the loss field by field. McWilliams says growers need to consider the yield loss incurred from replanting at a later date.

Yield losses from adapted corn hybrids in North Dakota and northwestern Minnesota are negligible until after May 15, when later planting will result in a shorter-than-normal growing season. In this northern area yield losses accumulate rapidly, from 7 percent or more through May 20, 13 percent or more to May 25, and 24 percent or more to June 1.

With soybeans, yield losses of adapted varieties in the Red River Valley are usually negligible until May 20. Depending on weather, possible yield loss can be around 13 percent from May 26 until June 9, when late planting losses can be around 24 percent. Soybeans planted as late as mid-June can have a 43-percent yield loss or greater compared to more timely plantings.

McWilliams stresses that replant considerations vary across farms and locations. Growers need to carefully weigh potential yields from a replanted crop against current plant stands, and base decisions on current crop pricing.

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Source: Denise McWilliams (701) 231-8160

Editor: Gary Moran (701) 231-7865

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