It is difficult to know when to harvest frost-damaged corn because of differing degrees of plant damage in the field. Corn that has experienced a killing frost at the early dent stage of maturity will generally contain moisture content below 72 percent and should be harvested immediately.
But what about corn frosted at an earlier stage of maturity?
The commonly used "kernel milk line" guidelines are not as indicative of moisture content in frosted silage. The moisture content will vary with the stage of grain maturity and the degree of freezing. Corn that experiences a killing frost in the blister or milk stage of development will likely contain moisture content in excess of 75 percent.
Although the loss of leaves gives the appearance of rapid dry down, most of the moisture is in the stalk and grain. Frosted corn often appears to be drier than it really is. Immature, frozen corn does not dry down significantly faster than unfrozen corn, and may require many days of drying to reach the correct moisture content.
If a substantial percentage of kernels have been frozen and appear watery or discolored, then those non-viable kernels will not deposit any further starch. However, if the majority of the kernels on the ear look normal, they can continue to deposit starch from the photosynthetic activity of the leaves that avoided the frost.
Having the top leaves frosted will reduce photosynthetic capacity and diminish the starch-producing potential of the plant. However, if the majority of the leaves around the ear are still healthy, they can contribute to additional starch deposition.
It is highly recommended to allow the plants to dry down to below 72 percent before harvesting, or add dry materials such as dry ground grain or grain byproducts like dried distiller grains, corn gluten, or dried beet pulp, to dilute the moisture content to below the 72 percent.
A good rule of thumb is that adding one bushel of dry grain per ton of silage will increase the dry matter content of the silage by approximately 1.5 percentage units.
Whole-plant moisture generally decreases by about 0.5 percent per day during September. Frosted corn silage can begin to develop spoilage organisms in the field if warm weather follows the frost. Producers need to monitor this closely as these yeasts and molds can affect the ensiling process and may result in poor quality silage.
Immature corn with lower levels of kernel starch will typically have higher levels of untranslocated sugars in the stalk, helping improve energy density but also serving as a medium for spoilage organisms to thrive during feedout. Treating this silage with an inoculant containing an L. buchneri strain is highly recommended.
For more information, visit the Pioneer Silage Zone Harvest page.