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Veteran Advisor

Bean Damage Information

Assessing Frost Damage in Soybeans


Duane R. Berglund, NDSU Extension Agronomist

Soybean tops are easily damaged by frost in the 30 F to 32 F range. Temperatures under 30 F for any extended period of time can completely kill soybean plants (stems and leaves). Generally speaking, the soybean fields planted to narrow row spacing (6-7 inches to 15 inches), may have slightly more tolerance to light frosts than soybeans planted in wider rows (30-36 inches). Also soybean plant populations that have thin stands are more affected and injured by frost.

The thick plant canopy of the solid-seeded, closely drilled beans tends to hold the soil heat better and protects the lower portion of the plants and developing pods to some degree. Pods in the lower portion of the plant should continue to fill beans and develop normally. Some maturity delay may occur. Some small pods in the upper area of the plants may not fill normally and can abort in some cases.

Beans that are still green and soft will shrivel. Stalks rapidly turn dark green to brown and will not recover. Beans in pods that have turned yellow will mature normally. Some green beans will turn yellow after 30-40 days of storage.

Growers and researchers over the years have tried color keys of yellow soybean leaves, yellow pods and brown pods to estimate soybean maturity and safety from frost. Usually these methods didn't work because of differences in varieties of indications of maturity.

However, studies do show that "yellow" pods sprinkled with brown are the best clue of physiological maturity. It is suggested to open pods and check shrinking of beans and look for separation of beans from the white membrane inside the pod. This indicates the soybeans are physiologically mature and fairly safe from frost injury. All pods do not mature evenly.

It's been noted that if one or two pods on any of the upper four nodes have turned brown in color, and other pods are light yellow to tan, the soybeans are fairly tolerant to a killing frost.

Research information from Wisconsin has shown that all varieties tested had reduced yields when frost occurred at or before R6. Earlier maturing varieties sustained economic yield losses from frost at more advanced growth stages than later maturing varieties. The greatest yield losses occurred when frost occurred at stage R5. The number of beans per plant and reduced bean size all contributed to overall yield loss. Maturity was hastened by some frost treatments and was not delayed in any of the trials studied.

The leaves do remain on the frost damaged soybean plants. Seed moisture may be slightly higher and seed size usually is reduced as the soybeans dry and shrink. A frost will not hurt soybean yields if the soybean growth stage is beyond R7. A frost between R6 and R7 may or may not affect yield, depending on the temperature and duration of the freeze.

In the event of a leaf-killing frost, when pods are still light green or yellow, wait until the pods are mature in color before combining.

The most significant effect of an early frost on soybeans may be in the reduction of quality to use as a future source of seed.

Table 1 shows growth stages and potential yield losses of a killing frost on soybeans.

Table 1.  Percent of yield produced by various soybean growth stages and calendar days between growth stages.

Growth Stage

Days after bloom begins

Days to maturity

Percent of total

Begin Pod (R3)


68 --

Full Pod  (R4)


 59 --

Begin Seed  (R5)


 50 25

Full Seed  (R6)


 35 47

Begin Maturity (R7)


 10 95

Full Maturity (R8)


 0 100

**Note this is  for full, late maturity soybeans in southern Minnesota.

-Source: University of MN  reported at

If all leaves on a soybean plant are killed between full seed stage and beginning maturity, 53 percent or less of yield can be lost. A freeze before maturity has less effect on yield the closer the freeze date is to mature date.

Air temperatures of 29 F are necessary to completely kill corn and soybean plants.

If frost is so severe that the majority of the grain yield has been lost, then harvesting for soybean hay should be considered. Check with your insurance agent and FSA-USDA office before harvesting or destroying the frozen crop.

10 Replies
Veteran Advisor

Re: Bean Damage Information

I don't know how much crop the last few days.  I suspect that it is more than the trade thinks at this point.  There are going to be areas that were killed, but that is going to be realitively small, all things considered.  If it had been dryer, it would've been a catastophe.  As a matter of fact, several have said how weird this frost was.  Comparing a field that froze, and one nearby that didn't, it's where I would start.  Was the field that froze overall drier?  Did it have more dry matter on the surface, corn stalks, leaves, etc., that would have helped hold in the moisture, and allow the upper area to frost, or freeze.  I saw this one year.  We had a Fathers Day frost in Central WI, and I had cultivated part of a corn field the day before.  The field froze right to the line -  it was really strange - but, it showed me quite definitely the difference between dry ground and that which was moist.  I would be interested to see what you find out there.


There are  some areas that are going to be real bad.  I think SE MN and into IA got hammered.  I haven't been able to get hod of anyone yet over by Cannon Falls, but I don't think that area was too bad.  Where I saw the temps down was in the Rochester area.  I'll be going home next weekend, and will get to see some of the damage first hand.


I know this has been a trying few days.  Some thought that it really wouldn't frost, even though I repeated said what a problem we were looking at.  I know what I saw up in Canada, and I know, without having first hand sight of the damage, know that it is bad up there.  I'm not sure about ND or SD, but I'm sure, that there too, there has to be damage.  We can all be very lucky that the air mass warmed enough the next night to not only hit the new area farther East, but it was supposed to hit the same area as the night before, which would've been really bad also.  We got lucky.  I could've been very, very much worse.



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Re: Bean Damage Information

Believe it or not, but we had scattered frost in KS. Some fields showed damage.
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Veteran Advisor

Re: Bean Damage Information

thanks Jen,


crunching some #'s - 39 mil ac were potentially affected - say only half of that actually frosted and was R6-6.5 or less - 20 MIL AC POTENTIALLY?


OR ABOUT 23%  hmmmmm. if that 23% or 19 mil ac took an avg 25% reduction we come out with about 3.692 B bu


Sep = 3.913 - 3.692 = 220 mil bu. seems reasonably conservative - if same area takes a 37.5% reduction - half R6/R5 = 29 bpa X 20 mil ac = 582 + 3007 (64 mil ac @ 46.6) = 3.589 B bu...3.913 - 3.589 = 320 mil bu.


however, trick is the OTHER 64 mil ac could avg HIGHER than 46.6 Smiley Wink i'm hearing about some good yields elsewhere

-like some 80+ in central IL..................


price still holding 994-995 - i think bean crop's not getting bigger from here at least. 00:37 hrs - time to go to bed.

Veteran Advisor

Re: Bean Damage Information

C-X-1, we probably didn't lose 25%, more like 15-18%, factoring in the complete kill areas.  But, it will be a while yet before all the loses are known.  We have other issues also with the beans - ie., like Hobby said, a lack of sunlight.  Beans are very sunlight dependant for the development of the pods and beans, and will affect the size.  Stunting.  We need heat units to pull these plants out of the frost shock, and make them think that all is OK.  And we still need heat units.  I don't have time this morning, it's my second double day - gotta get to work.


One quick look at the morning markets.  I see we're up 8 - 10 on the beans.  Where's our gap down, VR?



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Veteran Advisor

Re: Bean Damage Information

With the above being said, I don't think push up here of any size right now can be expected. I do agree with most, that we probably have more down side to deal with. Obviously, the down side objectives of this market have not been met, but the frost event is probably enough to hold here, until more is know about what the loss was. Right now, it's all speculation. But we were trading at record crops for corn and beans. Many people have said all year that the beans didn't look good, and were behind. This frost certainly didn't add bushels.

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Esteemed Advisor

Re: Bean Damage Information

Jen, its a good thing the frost didnt come any further east, we have had our own soybean issues. We didnt get much rain in August, and some of the guys that irrigated are having white mold issues. Probably another disappointing soybean year for me.

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Senior Contributor

Re: Bean Damage Information

How big of an area was the unexpected frost this A.M. lots of white here.

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Re: Bean Damage Information

Where are you at crop hugger?
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Re: Bean Damage Information

One post started by someone with 4 out of eight responses by the same person in the thread. Are there problems here.
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