Frost and Cold Temperature Damage to Small Soybeans

Frost and Cold Temperature Damage to Small Soybeans

  • Soybeans respond differently to frost compared to corn because the growing point is exposed to weather as soon as the cotyledons emerge.
  • Understanding the effects of weather conditions on soybean at different growth stages can help determine the best management options.

Soybeans vs. Corn

Soybeans are more susceptible than corn to frost and cold temperatures. The growing point for corn remains below ground until corn reaches about V5 (5 visible leaf collars) growth stage. Comparatively, the growing point for soybean is above ground and exposed to the elements as soon as the cotyledons emerge.

If the main growing point (also called the apical meristem) is damaged, soybeans have a greater ability to recover than corn. Soybean plants can produce new growth auxiliary buds found at each node. When this regrowth occurs from the node where the cotyledons or unifoliate leaves were attached, it has been referred to as psi syndrome due to the shape.

Will the Soybean Plant Make It?

Frost damage to soybean plants can occur when temperatures range between 28 to 32 °F. Temperatures of 29 to 30 °F may be tolerated for short periods of time when soybeans are in the VE (emergence) to VC (unrolled unifoliate leaves) growth stages. Several days of cool temperatures can harden a plant, and when this occurs, temperatures of 28 °F may be tolerated. Complete death (buds, stems, and leaves) is not expected until temperatures remain at 28 °F for an extended period of time for sensitive plants. Soybeans in the VC stage are slightly more frost tolerant compared to soybeans in the V1(first-trifoliate) and V2 (second- trifoliate) growth stages. Soybeans with emerged trifoliate leaves (V1 and V2 growth stages) become more susceptible to temperatures below 32 °F for any extended time.

Patience is needed to determine if an individual soybean plant is likely to survive a frost. It helps to wait a few days before evaluating the potential for new growth at the auxiliary buds. In Figure 1, the plant on the left has been injured by frost for 24 hours and may have tissue death below the cotyledonary node. The plant on the right was injured by frost, but only down to the area above the cotyledonary node, allowing for regrowth from the auxiliary buds at that node. The growth from those auxiliary buds will be similar to that of the original plant had it not been damaged by frost. The odds of the injured plant on the right producing a respectable yield potential are very good.

Figure 1. Examples of frost damage to soybeans. Plants with severe frost damage that begins below the cotyledonary bud (left) may have tissue death. If regrowth at the cotyledonary node is seen (right), plants may contribute to yield.

Will the Soybean Plant Make It?

Replanting a field of frost-damaged soybeans demands more consideration since soybeans are more susceptible than corn to frost and cold temperatures. However, soybeans can tolerate stand reductions fairly well. Often, if a soybean stand is evenly distributed, replanting is not recommended unless populations are less than 100,000 plants per acre. As the season progresses, vigilant scouting should continue for seedling blights and environmental damage in soybean fields, especially those damaged by frost.

There are many resources available addressing soybean early growth and survival. Additional information on evaluating soybean early growth and survival can be found in the video blog developed by Extension Specialist Shawn Conley at http://ipcm.wisc.edu/blog/2014/05/new-video- soybean-emergence-and-germination-common-issues/.

Sources: Berglund, D.R. 2004. Spring frost damage to crops could be a problem. News. North Dakota State University. www.ext.nodak.edu. 120601023004

For additional agronomic information, please contact your local seed representative. Developed in partnership with Technology Development & Agronomy by Monsanto.
Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ©2017 Monsanto Company.120601023004. 051215SEK

Stalk Lodging

For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is subjected to stress during grainfill, photosynthetic activity is reduced. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this “cannibalization” process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi. As plants near maturity, this removal of nutrients from the stalk to the developing grain results in a rapid deterioration of the lower portion of corn plants with lower leaves appearing to be nitrogen stressed, brown, and/or dead.

Stresses which increase the likelihood of stalk rot problems include: loss of leaf tissue due to foliar diseases (such as gray leaf spot or northern corn leaf blight), insects, or hail; drought; injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium; compacted or saturated soils restricting root growth; and high plant populations.

Most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity. It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot.

The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvested promptly. It’s not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms. Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to weathering, e.g. strong winds and heavy rains. I like to say that we are only one storm away from stalk rot/lodging “awareness”.

A symptom common to all stalk rots is the deterioration of the inner stalk tissues so that one or more of the inner nodes can easily be compressed when squeezing the stalk between thumb and finger. It is possible by using this squeeze test to assess potential lodging if harvesting is not done promptly. The push test is another way to predict lodging. Push the stalks at the ear level, 6-8″ from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present.

To minimize losses for stalk lodging rot damage, avoid harvest delays. Identify fields that are at greatest risk and harvest these fields first. Fields which experienced late season drought stress or extensive northern leaf blight or grey leaf spot would be prime candidates for early harvest. It will be tempting to take advantage of good weather, but it rarely lasts past the third week in October. And please remember that November is the wettest month of the year!

October 2015 Earfull Newsletter
Written by Jeff Renk