Freeze Injury to Corn and Silage

What temperature is the threshold for freeze injury to corn? Can field conditions affect this?

• At 32 °F (0 °C), corn can be killed after several hours of exposure.
• At 28 °F (−2 °C), corn can be killed in only a few minutes.

Frost can damage corn plants when temperatures are near 32 °F (0 °C). Damage is especially likely if rapid heat loss occurs which, for example, can happen in environmental conditions such as clear skies with no wind. Variations in field topography can also alter the microclimate around individual plants or areas of a field, which may cause low areas to be more prone to frost or freeze injury.^1,2

What are the signs of freeze injury and when should corn be checked for them?

The sign of freeze injury is water-soaked leaves that become brown. This symptom usually takes at least a day to three days to appear, so injury assessment should occur about five days after the cold weather event occurs.¹

Will the grain quality be impacted by freeze injury?

The extent of the impact of freeze injury on grain quality depends on the plant’s growth stage when injured and the amount of damaged leaf tissue. If the grain is in the mid-dough (R4) growth stage, the impacts on quality can be substantial. If corn is completely killed by frost at this stage, the average loss of yield is about 55%, while a light frost that only kills leaves at the R4 growth stage may cause a 35% loss of potential yield. If the grain is in the dent stage (R5), the impacts are usually moderate. When the grain is in the R5.5 stage (half-milk line), freeze injury will typically cause only minor impacts to grain quality and average yield potential losses of 12% if plants are completely killed or 5% if leaves are only damaged by frost.^1,2

If the plant is not completely killed but the leaves are damaged, will the stalk provide resources to the developing grain?

If the stalk is alive after the frost event, it can provide carbohydrates to the grain. While this may reduce grain yield losses, the cannibalization of stalk resources may increase susceptibility to root and stalk lodging prior to harvest. In these situations, growers should monitor stalk quality and use it to determine harvest timing.²

Will field drydown rates be impacted after a frost event?

The drydown rate of frost-damaged corn should be normal. However, if the grain was frozen before full maturity, it may take an extra 7 to 10 days for grain to reach the 22 to 30% moisture range.^1,2

What are the characteristics of frost-damaged grain?

The grain will be soft, small, oddly shaped, easily broken, and can generate many fines. The starch will be undeveloped and have a “pithy” appearance. Protein content will be average at a test weight above 45 lb/bushel but will be reduced along with digestibility at lower test weights. Test weight will not increase after grain drying. When the moisture levels of immature frosted corn are checked with grain moisture meters, the moisture readings from the meter tend to be lower than the actual values observed when the grain is dried.¹

What is the best use of frost-damaged corn grain?

Frost-damaged grain is best used as animal feed, so the grain is best tested for protein and amino acid levels, as well as mycotoxins if the grain has low test weight. Frost-damaged corn with a test weight below 45 lb/bushel, is likely only 2 to 5% less valuable than normal corn as feed for large animals.¹

Unlike its usefulness as animal feed, frost-damaged grain is less useful in ethanol production. Indeed, ethanol millers usually will not want to take frost-damaged light corn, as it is not as efficient or predictable as normal corn in the milling and fermentation processes.¹

Can frost-damaged immature grain be stored?

Yes, but care must be taken in drying and storing frost-damaged immature grain. Achieving a consistent grain moisture level with the grain drier will be challenging, as grain moisture levels from the field will be variable. Reduce dryer air temperatures to below 160 °F (71 °C) and store grain with at least 14% moisture. Cooling the grain mass slowly after artificial drying to a storage temperature of 20 to 30 °F (−6 to −1 °C) can also help with quality concerns.¹

If possible, keep immature frost-damaged grain separate from normal grain, as frost-damaged grain can go out of condition quicker and its storage life is only about half as long as normal corn. Keep the bins aerated as much as possible and use or sell the grain before the summer months.¹

What impact will a killing freeze have on corn to be used for silage?

If the corn was frost-damaged or killed prior to the dent stage, plant moisture will be too high for ensiling. Allow the crop to dry in the field for several days while monitoring whole-plant moisture. If the corn was in the dent stage, harvest should begin as soon as possible, both because excessive leaf loss can occur after frost or freeze injury and because complications can occur if mold forms on ears or grain due to the increased moisture. Corn silage can be mixed with straw or chopped to reduce the overall moisture level. A rule of thumb is that about 30 pounds (14 kg) of dry material per ton of silage is needed to reduce the silage moisture by one percentage unit.^1,2

Is checking the whole plant moisture necessary if the plant is killed by frost?

Absolutely. A frost-killed plant may look drier and give the false impression that it is ready for harvest. Using the whole plant will provide a more accurate measure for determining if the corn is acceptable for ensiling.

Will nitrate concentrations be too high in frosted corn used for silage?

Perhaps. If the plant is still alive and photosynthesizing, even if it is just the stalk, it may accumulate nitrates—particularly in the lower stalk. Cutting the silage higher, at around 18 inches (45 cm), can reduce the risk. Harvesting at this height will lower yield but will also improve quality, as the corn stalk below this height is wetter and of poorer quality. Cutting at 18 inches (45 cm) decreases whole plant moisture by about 4%, decreases tonnage by about 10 to 15%, and increases quality by about the same percentage as the decrease in tonnage. This results in a milk per acre yield reduction of 3 to 4%. Green chopping may also be a way to salvage the frosted corn if it is not at ensiling moisture levels, but again, nitrates may be a concern with this method.^1,3

Sources

¹2014. Frost. University of Wisconsin Extension. https://corn.agronomy.wisc.edu/Management/L041.aspx

²Nielsen, R.L. 2019. Frost or freeze damage to immature corn. Purdue University Extension. https://www.agry.purdue.edu/ext/corn/news/timeless/FrostFreezeImmatureCorn.html

³Singh, M. and Cassida, K. 2019. Management guidelines for immature and frosted corn silage. Michigan State University Extension. https://www.canr.msu.edu/news/management-guidelines-for-immature-and-frosted-corn-silage

Web sources verified 09/11/25. 1222_153609