Iowa Soybeans: Frost Damage – What to Expect

Snow covered soybeans. Photo: Angie Peltier, University of Minnesota

Temperatures fell into the low 30’s and upper 20’s in most of Iowa over the weekend of October 11-13.  Because of the very late planting season, there were some crops immature enough to be injured by the freezing temperatures.  Soybeans normally are more vulnerable to frost damage than corn.

Frost normally forms early in the morning, driven radiation cooling especially on clear cold nights.  The visual impact on plants, and quality impact on the grain, is most evident the next day.

Don’t panic is the first statement I give to producers. Marketing them immediately will result in the worst grain discoloration and the highest moisture.  If you harvest the field right away, put them in an aerated bin. The greenness (chlorophyll) will subside somewhat over time with air and drying. Evaluate them for marketing after a period of aeration.

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Green damage (frost) is a category of Damage in the Grades, and will cause price discounts. But greenness must be fairly intense and comprehensive to be classed as damage. Below is the FGIS statement and example color photo about soybean frost damage.

There will be problems in grading…processors and elevators may call anything somewhat green as damage. Federal graders are trained in color differentiation. My advice is to take five samples or more, with varying degrees of greenness, to an Official Grader to “calibrate” grading at the elevator or processor.

Some processors use Official graders so they will have fewer issues. Processors will be concerned about green soybeans because of the likely lower oil yield, and the need to remove the green color from the oil by more intensive refining.

Farm moisture meters and older elevator meters will read low until moisture and color has equalized. The new style 150 mhz meters used by many elevators will be more accurate.


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