How much cold weather can be tolerated by new corn hybrids?

May 5, 1994 1(7):66

Joe Lauer, Corn Agronomist

Given the recent history of Wisconsin weather around corn planting, there has been some concern about possible cool, wet conditions and the effect these conditions may have on corn planting, germination and emergence. Corn germinates best in soil temperatures greater than 50 F with a sharp decrease at temperatures below 50 F. Germination is slow in cool, dry soils and will speed up as soil moisture increases until the soil is at field capacity. Saturated soil conditions will prevent or retard germination because oxygen concentration, which is required for germination, is too low around the seed.

Before germination, the seed imbibes water and swells. With warmer temperatures less water has to be absorbed, so that germination will start earlier and progress faster at higher temperatures. The first structure to emerge from the seed is usually the radicle (root) followed by the shoot. Growth of the radicle and the later emerging shoot is greatest around 86 F. Growth of these structures effectively ceases at temperatures of 48 and 104 F. Corn usually emerges in 8 to 10 days when soil temperatures average 60 to 64 F. It takes corn longer to emerge when soil temperatures are cooler (about 18 to 20 days at 50 to 55 F). Emergence has been known to occur in as little as 4 to 5 days when soil temperature and moisture are optimum.

Deeper planting can delay emergence. A general rule of thumb is one day delay for each one inch deeper depth. Since spring soil temperatures decrease with depth, emergence delays could be the result of both cooler temperatures and greater distance for the shoot to travel.

Cold, wet weather has been the experienced by Wisconsin growers over the last couple of years. Seed roots and seedling blight may become prevalent when corn is planted in wet soils below 50 F. For example, some species of Pythium are active at these temperatures. However, seed rot and seedling blight will occur infrequently when using good quality seed and proper seed treatment. Later planting may be encouraged to reduced seedling diseases, but this practice should be promoted with caution because delayed planting will reduce yield and quality. Delayed planting could also predispose the plant to potentially greater yield losses by other pests such as corn borer.

Some final thoughts about possibly planting into cool, wet soils:

  1. Previous experience with "ultra-early" planting date studies in Wisconsin has indicated that corn can take 20 to 30 days to emerge. Seed of modern hybrids will still produce good stands, even after a long time between planting and emergence.
  2. Final stands in the "ultra-early" planting studies were about 80 to 85 percent of the seeds planted. A grower who is concerned about cool, wet spring soils may want to increase seeding rates slightly to offset potential stand loses.
  3. Use only high quality seed that is treated. Don't plant last year's leftover seed until later.
  4. Plant shallow -- 1 to 1.5 inches or to moisture. Soil temperatures tend to be warmer near the surface, but temperatures also tend to fluctuate more.

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