Stalk quality can be defined as the ability of the plant to stand intact through harvest, after grain fill is complete and the plant is dead. Stalk quality is an issue in the eastern and southern United States where heat and high humidity stimulate leaf disease and stalk rot, causing corn plants to lodge. The two sources of stalk quality in corn are thick stalk rind and staygreen.
A hybrid with a thick rind has excellent stalk quality. It is not the diameter of the stalk but the thickness of the outer rind that provides resistance to lodging. The rind is made of lignin, which provides the rigidity that keeps the plant upright during the harvest season. Lignin is not metabolized by the saprophytic, soilborne organisms that cause stalk rot.
Developing high-lignin, thick-rinded corn plants through plant breeding is easily done. However, the yield potential of thick-rinded corn hybrids can be limited because the nutrients required for building thick rinds cannot contribute to yield.
Corn silage produced using hybrids with thick rinds is low in feed quality because lignin is low in digestibility. As a rule, the high-digestibility hybrids recommended for corn silage have thinner rinds and can have issues with stalk lodging if left standing in the field for grain harvest.
To develop hybrids with both high-yield potential and acceptable stalk quality, plant breeders select genetics with late-season disease resistance that enables hybrids to stay green and alive until grain fill is completed. Hybrids that stay green and alive in the fall fight off stalk-rot organisms that attack dead corn tissues. Corn plants staying alive in the fall, after grain fill is complete, continue producing plant nutrients. With grain fill complete, these late-produced nutrients are sent to the pith, the inner tissue of the stalk, adding support to the rind and assisting in lodging resistance.
The Eastern, Tropical, Early Health and Late Health Genetic Families are the best sources of late-season plant health and staygreen stalk quality. The Late Health Genetic Family has the best staygreen of all; however, it can lose staygreen strength if the growing season is rust-friendly. Rust causes ruptures in the leaf surface of the Late Health Genetic Family, allowing the entry of pathogens that Late Health usually resists. Therefore, in a growing season with rust, the Late Health Genetic Family can lose its staygreen characteristic.
Eastern, Northern and High Yield Genetic Families are the best sources of thick rind strength. Hybrids containing Northern/Eastern combinations have the best total stalk quality. Southern and Western genetic types tend to have little rind strength and poor staygreen, requiring complementary genetics that contribute staygreen. Placing Southern and Western genetics on well-drained soils with adequate fertility keeps them out of stalk-rot-producing environments and reduces their risk of poor stalk quality.
Tropical types are relatively new to the United States and are not adapted to its high plant populations. Pushing plant populations with Tropical types usually lowers yield potential and increases stalk lodging problems because they were developed in lower-yielding environments where reduced fertility levels were utilized. When using Tropical types, it is important to look at the other genetic families that are part of the hybrid and then adjust the plant population accordingly.
Plant breeders create test plot–winning hybrids by selecting staygreen stalk quality along with yield potential. However, staygreen fails to provide resistance to stalk rot when the corn plant is prematurely killed, such as during an early frost. In this case, stalk-rot pathogens attack the dead plant tissue and cause lodging.
Thick-rinded hybrids provide the best stalk quality when maturity for the zone is stretched. Northern x High Yield genetic types work best in early frost or when heat units are below normal because they do not rely on staygreen for stalk quality and have genetics built for cool weather. However, during a cool season, some of these hybrids may run into test-weight problems because they are full season.
Another strategy for improving stalk quality is planting hybrids with increased ear flex, which allows a reduction in plant population. Lower population promotes shorter plant height, increased rind thick-ness and lower ear placement. This reduces the risk of poor stalk quality, along with the risk of heat and moisture stress as well.
Rotating hybrids in the same field from one year to the next is strongly recommended for improving stalk quality. Diseases and insects to which that specific hybrid is susceptible develop during the first year. At planting in the second year, every insect and disease to which that specific hybrid is susceptible is present in the field from day one; early death, poor stalk quality, low grain yield and low test weight follow.
On corn-following-corn acres, a reduction in risk is obtained when rotating genetic families in the hybrid from one year to the next. Usually a Southern type would be best the first year, especially if following soybeans or alfalfa, where there would be a response to the carryover nitrogen. The second year, a High Yield x Northern or a High Yield x Eastern would not only have improved rind strength, but the genetic families would be rotated as well.
Low soil fertility is another staygreen limitation. During grain fill, high-yielding hybrids require a large supply of plant nutrients. If adequate nutrients are not available, nutrients are removed from the lower leaves and stalk and translocated to the grain. If nitrogen is limited, interveinal chlorosis (typical nitrogen-deficiency symptoms) is visible in nitrogen-starved plants.
The movement of nitrogen from the stalk and leaves to the grain causes early corn plant death. Stalk rot invades the dead plant and causes stalk lodging. It is critical for high-yielding hybrids, dependent on staygreen for stalk quality, to be planted in fields with high fertility levels so nitrogen cannibalization and premature stalk death are avoided. This is especially true of Southern, Tropical and Late Health hybrids.
Careful field scouting during the fall can help identify stalk-quality problems. Hybrids staying green and alive late in the fall continue producing sugars after grain fill is complete. With the ear finished, these sugars move down into the pith, improving stalk strength. When the sun shines on stalks, sunlight reacts with sugars to produce a reddish-purple pigment. Fields with plants turning reddish-purple stand longer than fields with plants dying quickly after black layer development.
One outcome of increasing plant population is a reduction in stalk quality. Corn plants respond to increased competition by growing taller with smaller stalk diameter. Increasing population also elevates ear placement, which increases stalk lodging. The reduction in stalk quality as plant population increases is especially prevalent in Southern- and Tropical-influenced hybrids where poor rind strength can lead to stalk collapse. In Eastern types, high ear placement can cause both stalk lodging and root lodging problems, especially during high winds.
Test weight measures the density of the grain. High-density, high-test-weight grain typically receives less physical damage during harvest. High-test-weight grain is also less likely to develop ear molds caused by delayed harvest or heavy bird and insect feeding. Hybrids that stay green and alive in the fall have higher test weight than fast-die/fast-dry hybrids because they have more time for filling the grain. Southern, Tropical, Early Health, Late Health and Flint genetic types have the best test weight.
- Diseases and insects overwinter on corn residue, multiplying over the years.
- When diseases and insects prematurely kill the plant, stalk quality suffers.
- Standability in continuous corn is improved by planting hybrids that produce thick rinds, such as Northern and Eastern types.
- Southern and Tropical genetic types, planted at low population, work on continuous corn, but nitrogen rates must be monitored closely to ensure adequate fertility.
- Continuous corn frequently runs out of nitrogen during grain fill, since it lacks the late-season nitrogen release from a previous soybean crop in the rotation.