Chad Lee
Grain Crops Extension Specialist, University of Kentucky
September 30, 2003

Late corn plantings and cool autumn temperatures create a recipe for frost damage on corn grown for silage. The extent of the frost damage on the corn depends on the temperature, duration of the temperature and corn growth stage at the time of the frost.

Conditions for a Frost

Temperatures below 32 OF for 4 to 5 hours will result in frost damage to the stalk, leaf, and husk. Temperatures that drop to 28 OF for a few minutes and return to 32 OF can result in similar injury. Temperatures between 32 to 40 OF typically result in less frost damage.

Frost at temperatures above 32 OF usually occur under conditions of clear skies, low humidity, and no wind. These conditions are ideal for rapid heat loss from the corn leaves. Under these conditions, temperature of the corn leaves can be less than the air temperature. Thin stands of corn and corn stands at the edges of field are more likely to receive frost damage at temperatures above 32 OF than thicker stands and the centers of fields. The uppermost leaves of the corn plant are most susceptible to frost damage at temperatures between 32 and 40 OF. 

Growth Stage at Time of Frost

Corn will ensile well at moisture levels less than 70% for upright silos and less than 75% moisture for horizontal silos. Corn harvested at 62 to 68% moisture (late-dent stage) is ideal for ensiling. Frost damage prior to this stage will reduce yields and may reduce quality. Management of corn damaged by frost will depend on the stage of growth at the time of frost. 

Corn moisture content can be determined with a microwave or forage moisture tester. A very simple field technique for determining corn moisture content is to squeeze chopped corn in your hand for 30 seconds. Release the ball of chopped corn and examine its shape. You can gain a rough estimate of moisture content based on the descriptions in Table 1.

Table 1. Field technique for estimating moisture content of forage

Condition of Forage Ball

Approximate Moisture Content

When the ball holds its shape and there is considerable free juice

Over 75%

When the ball holds its shape but there is very little free juice

70 to 75%

When the ball falls apart slowly and there is no free juice

60 to 70%

When the ball falls apart rapidly

Below 60%

Frost at Milk Stage

If a frost occurs when the corn is at milk stage or early dough, then the moisture content of the plant is often too high for proper ensiling. The leaves of the plant will dry very quickly, which causes the entire plant to appear to be drying more quickly. However, the entire plant will dry down similarly to corn that was not injured by frost. If the corn at milk stage is ensiled immediately after frost, then nutrients will leach away, the silage will be sour and wet, and livestock consumption will be low.

Waiting to harvest frost-damaged corn at the milk stage will improve silage quality but will decrease dry matter yield. Up to 10% dry matter losses will occur the first ten days after the frost and up to 20% dry matter will be lost 40 days after the frost. In addition, mold may develop in the ears and cause further yield reductions. Because of these factors, a compromise between dry matter yield and ideal ensiling moisture must be made.

In some cases, the corn will need to be harvested when it is too wet for silage. In these situations, chopped grain, hay or straw can be added to the silage to decrease overall moisture. In general, 30 pounds of dry matter per ton of silage are required to reduce the moisture percentage by one point. For example, if the corn was at 78% moisture and the target moisture was 68%, then 300 pounds of dry matter would be required for each fresh ton of silage.

Another option for corn with high moisture contents is to feed it as green-chop. Cattle will consume less green-chop corn than ensiled corn. However, the quality of the frost-damaged, green-chopped corn is better than the quality of the ensiled corn at milk stage.

Frost at Dough Stage

If a frost occurs when the corn is at the dough stage, then the corn is often too wet for silage harvest. Typically, several drying days are necessary before corn will be at the proper moisture for silage harvest. The corn should be harvested as soon as it reaches the desired moisture of 70 to 75%.

Frost at the Dent Stage

If a frost occurs when corn is the early dent stage, then the corn may need to dry a couple days before it is ready to harvest. If a frost occurs when the corn is at the mid- to late-dent stage, corn is at or very close to ideal moistures for ensiling. Corn damaged by frost at the mid- to late-dent stage should be harvested for silage immediately.

Additional Questions

For additional questions regarding frost damage on corn grown for silage, contact your local county extension agent.

References

Bitzer, M. J., J.H. Herbek, G.Lacefield, and J. K. Evans. 1979. Producing Corn for Grain and Silage: AGR-79. University of Kentucky.

Carter, P.R. and O.B. Hesterman. 1990. Handling Corn Damaged by Autumn Frost. National Corn Handbook: NCH-57. Michigan State University.

Nielsen, R. 1996. Potential Yield Losses in Corn from Fall Frost Damage. Purdue Crop and Livestock Update: CL-9. Purdue University.

Taylor, R.W. and R. Barczewski. Managing Frost-Damaged Silage Corn. Agronomy Fact Series: AF-10. Delaware Cooperative Extension.