Decisions about managing frost damaged and immature crops need to be based on severity, crop maturity, available resources, insurance, livestock health, and other factors. The following resources may be helpful to growers to assess their options for their damaged or delayed fields.

This Year's Climate

On three consecutive mornings, August 19-21, 2004, record or near record low temperatures were reported around Minnesota. Some resulted in damaging ground frosts, while others resulted in a hard freeze, all but ending the growing season for some crops.

Yes, we have had frequent intrusions of high latitude arctic air masses this summer thanks to the persistent position and strength of a continental polar vortex. This makes us all nervous about early frost probabilities for a very slow developing crop.

Though the microclimate effect weighs heavily on the occurrence of frost, it is common to have a frost in a summer that is in the colder end of the distribution historically, just as the summer of 2004 has been. The Climate Prediction Center forecasts a cooler than normal month of September for Minnesota. This translates to a high likelihood for immature crops of relatively high moisture content. The prospect of making up for lost Growing Degree Days (GDD) is dim. The shortage of GDD is amplified by later planting dates since the growing season has essentially been consistently too cool to close the gap and draw GDD totals closer to normal. Many of the GDD totals remain over 20 percent behind normal.

The other feature of the September climate outlook worth mentioning is that Minnesota is expected to be wetter than normal. This may impinge on the ability of the crop to dry down before being harvested. So all the climatic indicators suggest that corn and soybean crops will not reach normal maturity, will likely be exposed to further frost or freeze damage, and will be of higher moisture content and require further drying.

Also see:
Examining growing season climates in south-central Minnesota

Early Frost: How common historically and did it end the growing season for some?

Map of Minimum Temps around State for August 21, 2004

Growing Degree Days and Corn Growth

Create Custom Growing Degree Day Summaries

Harvesting

When immature crops are damaged by frost, grain yield, drying rate, and grain quality can all be affected. Growers who are covered by crop insurance should check with their company rep before they do any harvesting.

The effect of frost on yield depends on how much leaf area is killed and the stage of development when the frost occurs. When only a portion of leaves are killed, those not killed can and will continue to function and contribute to yield if good growing conditions exist after the frost. For this reason, as well as high moisture, it is best to not harvest crops earlier than necessary.

University studies indicate that soybeans are injured by frost until they reach physiological maturity, which is generally attained at "yellow pod" or R7 growth stage. When the terminal growing point is damaged (by frost), re-growth can occur from the vegetative buds (growing points) located in the leaf axils on the main stem. However, the plant is also trying to fill the pods, and the crop is running out of time to compensate for the loss of foliage. Partly freezing when the soybeans have green pods 3/4 inch long, at one of the four uppermost nodes on main stem (R4 ) can cause a yield reduction of 70 –80%. Frost at the R6 growth stage and earlier, assuming that the plants did not completely freeze at this time, will result in a yield reduction and damaged beans with greenish color and wrinkled seed coats. Protein content should not be affected by frost; however oil content will generally be reduced if frost occurs before R6 (full seed). Fields should not be harvested until pods have a mature color, even if a killing frost occurred when the pods were green or yellow. Studies have shown that beans on frost-damaged plants will mature and change color at least as early and perhaps earlier than undamaged soybeans, however, the frosted, dead leaves will remain on the plant, and some beans may retain their green color.

The impact on corn yields will be different and will be dependent on the percent of the leaf area killed and the stage of kernel development. One can use the Corn Hail Yield Loss (included in Frost on Corn and Soybeans) charts to estimate the effect on grain yield by determining the stage of development and percent of leaf area killed. Kernel test weight should not be affected by 40 to 50% leaf killing at the milk to soft dough growth stages because kernels will abort from the ear tip due to the leaf injury. However, test weight will be lowered on those plants with 80 to 100 percent leaf killing. If test weight is not affected, kernel quality should also be good.

Some points to watch for in this year's corn harvest are are:

• Higher harvest moisture, which could contribute to slow and expensive drying.
• Uneven harvest moisture. Some fields or some parts of fields are likely to be wetter than others.
• Smaller corn kernels.
• Lower test weight.
• More chaff, fine material, and broken kernels.
• Poorer storability. The combination of more chaff, fines, and broken and cracked kernels could lead to greater risk of mold growth in storage.

Also see:
The Corn Crop – Frost and Maturity

Corn Test Weight Changes During Drying

Frost on Corn and Soybeans

Harvesting, Drying, and Storing Frost-Damaged Corn and Soybeans (Purdue)

Storage and Drying

After this cool growing season, both corn and soybeans may have high moisture at harvest. Soybeans, which are traded at 13% moisture, can be harvested at moisture contents up to about 18% without too much damage, although artificial drying is required. See Soybean Drying, Handling, and Storage. If harvesting immature, green soybeans, make sure to remove as much chaff and green plant material as possible before binning the beans. Immature beans can be stored without significant molding, but concentrations of green chaff can lead to heating in storage. Although it is commonly stated that green soybeans will eventually turn yellow in storage, the color change observed in a U of M laboratory study was minimal. It might still be worthwhile to store green soybeans for a few months after harvest though, to avoid the high discounts that are applied when large quantities of green beans are delivered during harvest.

This year energy costs are of special concern. For corn drying, some ideas for reducing energy costs include making more silage, letting corn dry in the field as much as possible, harvesting late and holding wet corn for silage, or using a slow cooling method. For details on these energy-saving methods, visit Drying, Handling, & Storing Wet, Immature, & Frost-Damaged Corn .

Immature and frost-damaged corn will have marginal quality, so it’s important to manage equipment carefully to minimize further quality degradation. Set combines carefully, to balance the need to get small kernels with kernal damage. Manage the fines and chaff, which can increase mold problems in storage. Dry grain to uniform moisture levels, a tricky business because harvest moisture is likely to be somewhat uneven after a cold, short growing season. Dry corn as gently as possible, even if it is tempting to crank it up for higher dryer capacity. Also, use slow cooling methods after gas-fired drying to minimize quality problems. If possible, aerate stored grain to cool it to 20 to 30F for winter storage (in the upper Midwest).

Also see:

Drying, Handling, & Storing Wet, Immature, & Frost-Damaged Corn

Drying Frost Damaged Crops (Iowa State)

Soybean Drying, Handling, and Storage

Post-Harvest Handling of Crops Web Site

Hay, Silage, and Animal Nutrition

Where frost injury occurred without complete kill, additional yield and forage quality accumulation is likely for the rest of the growing season from surviving plant parts. However, where these crops were/are completely killed by frost before reaching optimum grain or even forage harvest maturity, harvesting as forage is a viable option. In addition, based on the delayed maturation of corn and soybeans to date, chances are good that there will many acres of these crops that will receive a killing frost before reaching maturity, so harvest as forage may still be one of the better options as the growing season plays out.

Frost-killed, immature corn should be allowed to stand in the field until reaching proper moisture for chopping and ensiling. Ensiling immature, high moisture corn may require additions of an inoculant for fermentation and preservatives and conditioners to overcome high moisture and low carbohydrate levels. Corn in the blister stage may be as high as 80% moisture. Grazing is an option that may provide the means to capture the most nutritive value from standing, immature corn that is too wet to ensile.

Like immature corn, soybeans will also be too wet to ensile immediately after a killing frost. However, in contrast to corn, soybeans intended for harvested forage should be mowed and conditioned and left in a swath as soon after the killing frost as possible to retain leaves. It is too late to consider mowing-conditioning soybeans that may have been fully killed by the recent frost for silage or hay, but if a killing frost should occur before sufficient maturity for grain, ensiling after immediately mowing-conditioning into a swath and wilting or grazing may be viable options. Silage is preferred to hay for soybean because hay requires considerable wilting, is dusty, and stems are brittle, increasing feed bunk refusal. If grazing is considered, watch for bloat, which has not been reported by may be a possibility.

Note that some herbicides used on crops have label restrictions that prevent the crop being used as a forage.

Also see:

Check Corn Silage for Nitrates

Harvesting Immature Corn and Soybeans for Forage After a Killing Frost

Early Frost Means Be Alert to Prussic Acid in Forage Sorghums

Herbicide Forage, Feed, and Grazing Restrictions (.pdf)

Determining Moisture of Immature Corn Silage (Iowa State)

Corn Silage Maturity and Feeding Value of Frosted Corn Silage for Dairy Cattle (Purdue)

Negotiating the Value of Immature Corn Silage (Wisconsin)

Incorporation into the soil

Because of the severity of the frost in many areas of northern Minnesota there are soybean and corn fields that will not be harvested. Crops in these fields will probably be plowed under. If this action is taken, there are serious questions about the nutrient value of the destroyed crop. There are no research projects that provide data specific for this situation. However, we can apply information taken from other sources and adapt it to the damaged crop.

The phosphorus and potassium in the destroyed crop will become available to subsequent crops over time. This availability, if substantial, will be reflected in changes in soil test values, probably by 2005-2006. So, it is more important to sample fields when the destroyed crops have been plowed under.

We estimate a N credit for soybeans if destroyed at three states of development. These are:

• R3 - 25 lb. N per acre
• R4 - 45 lb. N per acre
• R5 - 65 lb. N per acre

An additional credit of 40 lb. N per acre should also be applied if a crop requiring nitrogen in a fertilizer program follows soybeans that are either harvested or destroyed. This credit is a consequence of factors other than the incorporation of soybean residue into the soil.

The amount of N contributed by a corn crop that is plowed under in the next two to three weeks (Aug 30-Sept 20) is more difficult to estimate. A nitrogen credit of 30 lb. N per acre appears to be reasonable for crops other than legumes that follow the destroyed corn in the rotation.

The N from the destroyed corn can be considered as a slow release source. This would be beneficial to wheat and other crops where quality is not a concern. Planting of barley after destroyed corn could be a problem. The late season release of N in 2005 could increase grain protein and disqualify the barley for the malting market. A sugarbeet crop would not be a good choice following a destroyed corn crop. Again, late season increase of N in 2005 would be a liability rather than a benefit because of the potential reduction in sugar content.

Soil sampled for nitrate–nitrogen is a recommended practice where damaged crops are plowed under. This sampling should be delayed as long as possible this fall. This delay will provide for a more accurate measure of mineralized N.

Also See:

Nutrient Removal by Corn and Soybeans and Nutrient Credits

Crop Insurance

If a farmer has purchased crop insurance, yield losses caused by the recent frosts may result in an indenmity payment, but that payment depends on the type of insurance purchased. To understand how potential indemnity payments are calculated, check out this brief paper: Estimating indemnity payments from crop insurance. We show how indemnity payments are calculated under three types of crop insurance (1) Multi-Peril Crop Insurance (MPCI), (2) Crop Revenue Coverage (CRC), and (3) Revenue Assurance with “fall harvest price option” (RA-HPO). For a longer discussion of crop insurance options and how to choose between them, check out this earlier paper: Utilizing Federal Crop Insurance.

Also see:

Handling and marketing frost-damaged crops (Iowa State)

 

For further information about managing frost damaged crops call the Farm Information Line at (800) 232-9077 or contact your local Extension Ag Technical Advisor. For web-related concerns, contact the webmaster.

The URL for this page is http://www.extension.umn.edu/frostdamage