Soybean Seedling Frost Damage and Cold Temperature Injury

Frost injury to soybean plants can occur when air temperatures range between 28 to 32 °F (Figure 1), although the effects of a given temperature can depend on the growth stage and condition of the seedling plants. Plants hardened by several consecutive days of cool temperatures may tolerate periods of 28 °F. Complete death (of buds, stems, and leaves) of sensitive plants is not expected until temperatures remain at 28 °F for an extended time. Temperatures of 29 to 30 °F may be tolerated for short periods when the seedlings are in the VE (emergence) to VC (unrolled unifoliate leaves) growth stages. Seedlings in the VC stage are slightly more frost tolerant compared to plants in the V1 (first trifoliate) and V2 (second trifoliate) growth stages, while soybean plants with emerged trifoliate leaves (V1 and V2 growth stages) become more susceptible to injury when temperatures are below 32 °F for any extended time.^1,2,3

Survival Potential from Soybean Seedling Frost Damage

Patience is needed to determine if an individual soybean plant might survive frost injury. Survival can be determined by waiting 3 to 5 days after injury and scouting to see if there is new growth at the auxiliary buds (Figure 2).^1,2,3

Figure 3 shows a seedling that has been injured by frost for 24 hours and may have tissue death below the cotyledonary node, as indicated by the purple discoloration. If injury does not include the cotyledonary node or the nodes just above it, there is potential for regrowth from the axillary buds.^1,2,3 Regrowth from the node where the cotyledons or unifoliate leaves were attached has been referred to as psi syndrome due to its Greek letter shape (Ψ) (Figure 4). Tissue growth from the axillary buds should progress like that of the original plant, had it not been damaged by frost. Seedlings with regrowth from axillary buds have the potential for a respectable yield.^1,2,3

Should Fields with Frost Damage to Soybean Seedlings Be Replanted?

The decision to replant a frost-damaged soybean field demands careful consideration, because soybean plant reduction can be well tolerated. Minnesota research showed yield potential for hail damaged fields was steady at 75,000 plants/acre with one-foot gaps.³ Final replant decisions should be based on plant population, distribution of the plant population, anticipated yield potential based on replanting date, and associated costs (seed, fuel, labor, crop protection chemistry). For additional soybean replanting information, please see Soybean Replant Decisions and Should I Replant My Soybeans?

As the season progresses, vigilant scouting should continue for seedling blights and environmental damage in soybean fields, especially those damaged by frost.

Soybean Plant Survival Versus Corn Plant Survival Potentials

The growing point for a soybean plant is above ground and exposed to the elements as soon as the cotyledons emerge. Comparatively, the growing point for a corn plant remains protected below ground until the plant reaches about the V5 growth stage (visible leaf collars for 5 leaves). The different locations and exposures of these growing points affect each crop’s ability to recover from injuries. As mentioned above, if a damaged soybean seedling has live tissue above the cotyledonary node, it has the potential for regrowth even though the plant’s growing point or apical meristem is above the cotyledonary node. If the growing point for a corn plant is injured or killed by frost—or any other injury—that corn plant’s productive potential has ended.¹ There may be some regrowth from the corn’s growing point area, but the only potential regrowth is non-productive tillers.

Sources

¹Nielsen, R.L. (Bob) and Christmas, E. 2002. Early season frost & low temperature damage to corn and soybean. Purdue University, Corny News Network Articles. https://www.agry.purdue.edu/ext/corn/news/articles.02/Frost_Freeze-0520.html
²Potter, B., Bongard, P., Naeve, S., and Gunsolus, J. 2018. Spring frost damage on soybean. University of Minnesota Extension. https://extension.umn.edu/growing-soybean/spring-frost#insect-and-disease-damage-541512
³Mueller, N., Hall, R., and Gustafson, K. 2019. Chapter 51: Assessing spring frost and hail damage. In D.E. Clay, C.G. Carlson, S.A. Clay, L. Wagner, D. Deneke, and C. Hay (Eds). iGrow soybeans: Best management practices for soybean production. South Dakota State University Extension. https://extension.sdstate.edu/sites/default/files/2020-03/S-0004-51-Soybean.pdf
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