Late corn and soybean plantings

Due to persistent rains and wet soil conditions, we’ve received questions about the advisability of planting corn vs. soybean after mid-June in NW Ohio. 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.

Corn is not recommended as a late crop after mid June. Soybean is an option until early July. Some exceptions to late plantings of corn might be if corn is being grown for silage rather than grain, and N and corn herbicides had already been applied..

Recent studies have shown that good yields are possible with corn planted as late as mid-June but as a rule 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 (Ohio Agronomy Guide online at  http://ohioline.osu.edu/b472/index.html). We lose about 1 to 2 bu/A of yield  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 soybean 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). Keep in mind that a 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/A and established in narrow rows (6 – 7.5 inch). 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 late planted both corn and soybeans. However, corn is highly susceptible to drought damage during pollination and early grain fill and 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 with late planted corn include:

• Higher corn grain moisture requiring artificial drying that will increase cost of production
• Lower test weights that may 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 and Japanese beetles (and second generation European corn borer damage, if the hybrids planted are not ECB Bt hybrids).  
• Greater foliar diseases injury. Losses to gray leaf spot may increase with later planting dates.
• Less effective N uptake. If conditions turn dry after planting, late sidedress N applications may be ineffective.