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Senior Advisor

Info on Frost damaged beans

This may need to be in crops section - but it dos affect marketing - so here go's - This is out of NDSU -


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

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6 Replies
BA Deere
Honored Advisor

Re: Info on Frost damaged beans

That is interesting Ken. The R7 may have unseen phantom harvest loses like sickle shatter and the smaller seed riding the pods out the back of the combine.

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Veteran Advisor

Re: Info on Frost damaged beans

One of the interesting parts of the article, and what I have seen myself over the years, is the leaves staying on the frost damaged plants.  It is a real quick way to tel lif a field was ready to freeze, or not, after the field has browned down.  I saw it a lot in Central WI, where we dealt with frost as a yearly event for the most part.  


Some years ago, I was talking to a farmer who took one of these early frosts in Central MN.  It killed the top of the plant, but not all of it.  But beans are so prolific, he said that the plant put on new growth, and reflowered, and set some pods.  Great, right.  Wrong.  He said it was a mess to combine, because of course there wasn't enough time for the new pod set, and there were 8% beans along with lima beans in the hopper.  He said it was terrible.  It's been a while since we had this early of a frost, I wonder if we could see some of that this year.  Personally, I have never seen that occur.  Like I said on my post below, I never worried too much about the beans if they were turning - not just streaks in the field, but the field overall was turning color.  I actually liked it, because it got me into harvest quicker with better weather.  But - if the beans are all still green when the frost occurs, it's a bad deal.  


I talked about MN and IA this morning, but the area is much bigger.  ND and SD grow a large amount of crops, and I think between yesterday and last night, it's over for a lot of the crops up there.  I was up there this summer as you remember, and reported on the crops being behind at that time.  I suspect this is going to prove to be a fairly big deal when it's all said and done.


Then we are going to have to add in the Canadian crops.  Ontario is going to be in a bad way a few days from now, and they stand to see their growing season end for all crops then, unless something changes in the forecast.  The Northern Tier problem that I talked about since last winter, if you recall, appears now to be a real case scenerio.  I think we took a lot of frost last night - and more to come.



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jen put the computer down

Go for a walk.  Start golfing, read a book, and quit obsessing with the innernet.

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Honored Advisor

Re: Info on Frost damaged beans

OK I have dealt with immature beans a few times.


In the past they have either refused or severely docked green centered soys around here.

 An out of round bean have not been a reason for dockage, just green centers or mold.


Slightly green centers will go away in a couple of months.


Really green beans can be "fixed",  they need to be put in a bin with a full air floor and when it gets to about 10°F freeze them. They will need put in an air bin because of the excess moisture trapped in them anyway. 


The freezing destroys the chlorophyll color.


I've had beans that I was told had no value and to just disc them.  I combined them anyway, the same elevator bought them three months later with no dockage. No they weren't pretty but they were "saleable"


Might get zeroed out by Fed crop but be salvageable.


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Veteran Advisor

Re: Info on Frost damaged beans

In Central WI, we used a lot of those beans also by roasting them and using them in cattle rations.  It was a pretty good use of the beans.  At least they didn't go to complete waste.


I did see some really crappy beans come in last year when I was working as the "scale girl".  We took them all - no discounts - but it was a new elevator and I think they wanted whatever business they could get.  Me - I felt they should have been discounted, some of them quite severely.  But, they went in the bin with the rest.   I'm sure they just got "incorporated" somehow.



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Re: Info on Frost damaged beans

I find a month in a bin is enough
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