The two-week-later-than-normal first frost that occurred last week helped eliminate possible frost injury on most crops, but not all. At one time it looked like it might be a much larger issue when crops were running way behind schedule until warmer temperatures and lack of rain made changes to the crop in August.
Joseph Petrosino, an agronomist for Stewart Seeds, Greensburg, says that only the very full season hybrids in the latest-planted fields or plots may be at risk to lose some yield, depending upon exactly what stage of development plants were in last week, and how cold it was in any one area. He found some hybrids in neighboring Ohio in a plot that were still at two-thirds milk line and hadn't reached physiological maturity. Those hybrids could experience some yield loss.
The biggest loser may be double-crop soybeans, although the extra growing window allowed many of those to reach maturity or get much closer than it once appeared that they might. Since planting was delayed because wheat harvest was delayed in some areas, not all fields of double-crop soybeans may have been fully mature when the frost hit.
Here's what you can expect if plant growth is stopped at various stages in soybean development. It's based on Kansas State University data from the early 1980s, but should still apply today, Petrosino says.
If plants are only at R4, or full pod, yield loss could be 70 to 80%. If they are making seed, at R5, potential loss drops to 50 to 70 %. If there is full seed, at R6, loss potential is more like 15 to 30%. If the plant reached R7 there may or may not be any loss. If there is lost yield potential, it may only be about 5%. If beans have reached full maturity, you wouldn't expect any yield loss.