LAMAR, Mo. — Cold nighttime temperatures and late planted soybeans has farmers wondering what will happen to plants and yield, said Jill Scheidt, University of Missouri Extension agronomy field specialist.
According to Clarke McGrath, Iowa State University Soybean Research Center, on average, a three-week delay in planting may result in a one-week delay in maturity. Summer weather patterns can push that one way or the other. Later-planted beans may have fewer nodes per plant because they put more distance between nodes while playing catch-up on vegetative growth.
Once flowering becomes heavy, plants slow their vegetative growth and put more energy into creating pods. Earlier-maturing soybeans will slow node production quicker than later-maturity beans. https://www.farmprogress.com/soybean/will-late-planted-beans-beat-frost
According to the Lamar Weather Station, minimum air temperature was 34 and 32.7 degrees F on Oct. 11 and 12, respectively. According to University of Missouri Frost Freeze Guide, the average killing freeze of 28 degrees F, usually occurs from November 1-7 in southwest Missouri.
According to Bill Wiebold, University of Missouri State Soybean specialist, plant leaves do not freeze at 32°F, but temperatures near 32°F will affect plant growth and may negatively impact tender plant and cell parts.
Soybean yield is protected from frost if the plants have reached R7 or physiological maturity. At R7, seed moisture is about 60% and some green color is still present in seeds. If a killing frost occurs before R7, leaves will remain on the plant making harvest more difficult. Soybean seeds will not change from green to normal yellow color, and green beans are often docked at point of sale. This green color may fade with storage, but a change in color is not guaranteed.
According to North Dakota State University, soybeans at R6 or full seed stage, are 75-80% moisture and have a potential yield loss of 20-35%, depending on severity of frost. As soybeans move forward in maturity stages, likelihood of yield damage from frost decreases. It is best to wait 2 or more days after a frost to make an assessment so damage may be fully expressed. Leaf damage in the upper and lower canopy indicate more severe frost damage; stems and pods may also be damaged. Stems may turn dark green to brown and if seeds are soft and green, they may shrivel, reducing size and test weight and slowing dry down. If seeds have reached maturity and have begun to turn yellow, they should dry down normally and quality should not be affected.
“It is ideal to harvest at 16% moisture, but harvest can be attempted at 18% moisture if soybeans are sufficiently defoliated, but drying is needed. Preliminary studies have shown that green soybeans do lost their internal green color, although surface color may lighten or mottle somewhat after weeks or months in storage,” said Scheidt.
For more information, contact any of these MU Extension agronomy specialists in southwest Missouri: Tim Schnakenberg in Stone County, (417) 357-6812; Jill Scheidt in Barton County, (417) 682-3579 and Sarah Kenyon in Howell County, (417) 256-2391.
— Jill Scheidt, University of Missouri Extension
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