Set Yield Expectations After Frost and Freeze Events

With early snowfall in parts of the U.S., early frost might be on your mind. While Mother Nature is the ultimate decider on when frost hits your area, you can prepare by knowing what frost does to immature corn and soybean plants.

When frost hits before corn black layer or before R7 in soybeans it can be a detriment to yield, storability and grain quality. Each of these need to be considered as you harvest, store and sell grain.

First, understand yield impact.

Corn considerations

If frost and/or freeze events hit corn before it reaches physiological maturity, black layer, it often means the grain will be higher moisture than if it had matured naturally.

A light frost of more than 28 degrees Fahrenheit for just a couple hours might only kill leaves, namely in the upper canopy. Freezes of 28 degrees Fahrenheit or less for a couple of hours will cause whole plant death, according to Iowa State University (ISU) Extension.

“Whether maturity is natural or induced by a frost, grain dry matter accumulation is finished,” said Mark Licht and Charles Hurburgh, with ISU. “Incomplete grain fill from a frost or freeze often results in corn with low test weight that is greater than 35% moisture.”

Yield losses are considerably worse when the corn is less mature because moisture transfer is cut off, meaning no more grain fill. If you get an early frost, ISU experts say to expect test weights in the low 50s to 40s. Dry down in the field will also take longer and may require bin aeration or dryers to achieve adequate moisture goals.

Estimated percent corn yield loss due to defoliation occurring at various stages of growth.
  Stage of growth Percent leaf area destroyed
  20 40 60 80 100
   Yield loss (%)
Tassel 7 21 42 68 100
Silked 7 20 39 65 97
Blister 5 16 30 50 73
Milk 3 12 24 41 59
Dough 2 8 17 29 41
Dent 0 4 10 17 23
Black layer 0 0 0 0 0
University of Wisconsin, derived from Vorst (1990)


Soybean considerationsIn addition, Licht and Hurburgh warn that because the outer portion of the kernel dries faster than the interior in frost-damaged corn, grain moisture meters likely are reading wrong. In many cases, grain moisture is 1% to 2% higher than measured, unless you use a new 150 mhz unit that many elevators employ. Also remember, if your test weight measures less than 53 pounds per bu. storage life drops rapidly. Stay tuned later this week to Agweb.com for storage tips.

When temps are below 32 degrees Fahrenheit it can damage soybean leaves and below 30 degrees Fahrenheit can damage pods, stems and seeds. Soybeans are killed by 28 degrees Fahrenheit temperatures, according to ISU

If soybeans are at R7, with at least one mature pod on the main stem of each plan, they’re likely to be less effected by the frost. Any fields with green pods are more susceptible to damage, however if leaves are all that were damaged, especially in the upper canopy, there will be minimal yield impact.

“If the frost was more severe and damaged the stems, pods and seed, the potential for reduced yield and quality is higher,” according to ISU experts. “In addition to reduced yield and quality, severely frost-damaged soybeans will dry down more slowly and be more likely to shatter at harvest.”

Read more on what frost events mean here:

Rude Awakening for Crops, Livestock as Plains See Temperature Swing

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