Persistent rains and wet soil conditions in parts of the Corn Belt have some no-tillers weighing whether they should plant corn or soybean after mid-June.

"These questions have arisen in part because some corn fields need to be replanted due to emergence problems, including soil crusting, possible herbicide injury, hail, ponding and saturated soil conditions," say Ohio State University Extension specialists Peter Thomison and Ed Lentz.

"Corn is not recommended as a late crop after mid June. Soybeans are an option until early July," the Ohio State Extension specialists say. Some exceptions to late plantings of corn might be if corn is being grown for silage rather than grain, and nitrogen and corn herbicides have been applied..

Recent studies have shown that good yields are possible with corn planted as late as mid-June. However, there’s likely to be greater yield variability with late-planted corn than late planted soybean. Moreover, given current corn and soybean prices and production budgets planting soybean is going to be more profitable in most situations.

"We can lose as much as 50% or more of our yield potential when corn is planted in late June," Thomison and Lentz say. "We lose about 1 to 2 bushels of yield  per acre with every day of delayed planting after the first week of May, with the yield loss increasing more the later it gets. There is an increasing risk of the corn crop not maturing before frost  — unless growers plant hybrids of considerably earlier maturity than those normally planted."

Yields of soybeans planted in late June are typically 65% to 75% of normal. Effects of soybean relative maturity on grain yield can be large for late plantings. A key consideration in late soybean plantings is planting the latest-maturing variety that will reach physiological maturity before the first killing frost. Generally, stay with the same planned maturity (unless it is earlier than 3.0).

A varieties with maturities of 3.5, 3.7, and 3.9 may be used until July 1 for northern, central, and southern Ohio, respectively. Planting rate should be increased to 200,000 – 225,000 seeds per acre and established in narrow rows (6 to 7.5 inches). If planting is delayed past June 15, a desired seeding rate may be 225,000 to 250,000 in narrow rows.

Weather conditions — especially adequate soil moisture — often limit the yield potential of corn and soybeans that are planted late.

"Corn is highly susceptible to drought damage during pollination and early grain fill," Thomison and Lentz say. "The potential for high temperature and water stress typically increases later in the growing season when late planted corn flowers. Because soybeans flower over a longer period, they’re usually less vulnerable to this type of injury. As a result, late planted corn is a riskier crop than soybean."

Some other factors to consider when planting corn late include:

  • Higher corn grain moisture requires artificial drying that increases the cost of production.
  • Lower test weights, which result in significant dockage, especially if a frost occurs before black layer.
  • Greater stalk lodging and stalk rots. Late crops may experience more stress during grain fill and weathering during dry down
  • Increased injury from silk-clipping insects like corn rootworm beetles, Japanese beetles and second generation European corn borer damage, if the hybrids planted are not Bt hybrids that control corn borers.  
  • Greater injury from foliar diseases. For example, losses to gray leaf spot may increase.
  • Less effective nitrogen uptake. If the weather turns dry after planting, sidedressing nitrogen may be ineffective.