May 15, 2017

​Managing Corn Plant Health to Maximize Yield Potential​​​​


Key Points

  • Increased plant stress can result in decreased plant health which can negatively impact yield potential.
  • Primary impact of increased plant stress is reduced photosynthesis which can result in plants with weaker stalks that are more susceptible to root and stalk rots.
  • Soil fertility and disease management can improve overall plant health and help protect yield potential.

What Determines Yield Potential?

Corn yield potential is determined by the number of ears per acre, the number of kernels per ear, and the weight of each kernel. Each stage in a plant’s growth marks a unique developmental period for each of these yield components. Stress that occurs at key growth stages can have a large effect on overall plant health, and therefore potential yield.

A critical period in corn growth and development with respect to grain yield potential is pollen shed and silk emergence. Severe drought stress during pollination can cause as much loss in yield potential as stress at any other time during the growing season.1 While much of the plant’s potential yield is determined prior to pollination, reaching that potential is accomplished during grain fill.1 Limiting stress during grain fill can help ensure plants reach their full potential.

Effects of Stress on Corn Plants

The primary effect of severe stress on late season plant heath is a reduction in photosynthesis. During grain fill, the developing kernels are the main recipients of the carbohydrates (sugars) produced by photosynthesis. When photosynthesis is reduced for any reason, the effects go beyond just a reduction in photosynthates. Under stress, corn plants will direct movement of photosynthates to the kernels, while sacrificing the cellular health of the stalk, leaves, and roots.2 Under severe stress, the plant can actually remobilize stored carbohydrates from the stem and leaf tissue to fill the developing kernels. This not only weakens the plant physically, but also makes the plant more susceptible to stalk and root diseases.2 Fields at highest risk for stalk rot include those that have developed ears with high yield potential due to ideal conditions during vegetative stages of growth, but experience severe stress that reduces photosynthesis during grain fill. Those stresses might include drought, defoliation by hail, nitrogen deficiency, foliar diseases, or even an abundance of cloudy days.2 The effects of plant stress can be intensified by sandy soils that have minimal water-holding capacity or by plants that have a restricted root system due to compacted soils, nematode damage, or corn rootworm feeding.

Another potential yield-robbing effect of late season plant stress is the risk for premature black layer formation in the kernel. When the black layer forms, no additional nutrients can flow into the kernel and drydown begins.


While there is little you can do to minimize stress from weather-related sources such as drought and hail, some types of stress can be mitigated with proper management and treatment.

Fertility. Adequate fertility is essential to maintaining late-season plant health. A common photosynthetic stress that can occur during late grain fill is nitrogen (N) deficiency which can cause leaf tissue to yellow and die. Wet conditions early in the season may have saturated fields causing a loss of N due to denitrification or leaching. Tissue loss during grain fill can reduce the plant’s ability to create photosynthate and also decrease the nutrients that can be remobilized to the ear.

Nitrogen should be applied according to crop need and is recommended to be applied two to three times per season, depending on growing conditions. Split applications can help reduce the chance of N loss through denitrification and leaching. Corn requires the most N during rapid vegetative growth, so applications of N should occur prior to this stage, or within the V5 to V8 growth stages.

Potassium (K) is a critical nutrient during pollination and grain fill. If K is limited, silk emergence may be delayed, possibly resulting in unfilled ear tips. Potassium is also essential for the plant to move energy from the leaves to filling grain. Low levels of K in combination with excessive N can also lead to higher levels of stalk rot. Apply K according to soil test results. Lower K values may occur in fields where crop residue is removed or in fields previously planted with a soybean crop, as soybean typically removes more K from the soil than corn.3

Diseases. Fungal leaf diseases (Figure 1) can have a significant effect on corn yield potential through reduced photosynthetic capability which ultimately affects standability and grain quality. Much of a corn plant’s energy from photosynthesis is produced by the leaves immediately surrounding the primary ear, it is important to protect those leaves from disease. Fungicide applications made prior the spread of a disease throughout the canopy can help improve overall plant health and protect yield potential. While maximum yield potential is mostly determined by the tasseling growth stage (VT), kernel fill can be influenced considerably by protecting the crop from diseases.

Figure 1. Cigar-shaped Northern corn leaf blight lesions (left) and typical rectangular-shaped lesions from grey leaf spot.

Regular and timely scouting is important to help prevent corn disease outbreaks. Reduced and no-till practices can increase the incidence of disease as does continuous corn. Both scenarios increase the amount of corn residue left on the field, potentially accelerating the presence of disease inoculum.4

Disease Management Considerations

Disease incidence can vary greatly from season to season. The following practices can help reduce disease pressure in corn:

  • Select corn products that have resistance to common disease problems in the local growing area.
  • Use a premium seed treatment to reduce seed rots and seedling diseases.
  • Rotate to other crops and remove crop residue and weeds to reduce plant material that may harbor populations of disease organisms.
  • Apply fertilizer according to soil test recommendations to promote vigorous and healthy plant growth.
  • Subsoil below the row to help lessen compaction that may impede root growth.
  • Use fungicides when needed to help reduce potential losses.5

Fungicide efficacy depends on accurate application rate, timing, and method as stated on the product label and disease presence in the field. Deciding to apply a fungicide should be based on scouting, environmental conditions, management practices, disease pressure, and potential economic advantage. Potential yield increase of the crop should cover the cost of the application.

Foliar fungicides are typically active for 14 to 21 days. An optimal application of a fungicide can protect leaves from fungal diseases during grain fill. When foliar diseases are controlled, corn may be less susceptible to stalk rots.

Beginning in August and September, growers should closely monitor problem fields for compromised stalk strength or development of severe stalk rots and adjust harvest schedules accordingly. Fields and/or products at high risk of stalk breakage should be harvested as early as possible to minimize the risk of severe lodging and harvest losses.

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1 Nielsen, R. L. 2000. Corn growth & development: What goes on from planting to harvest? Purdue University. AGRY 97-07. 2 Nielsen, R.L. 2011. Stress during grain fill: A harbinger of stalk health problems. Purdue University. 3 Potash & Phosphate Institute. 1997. A balanced diet of nitrogen, phosphorous, and potassium is essential for the development of a corn plant. Agri-Briefs No. 4. 4 Wise, K. and Mueller, D. 2011. Are fungicides no longer just for fungi? An analysis of foliar fungicide use in corn. American Phytopathological Society. 5 Kemerait, B. 2015. Corn disease and nematode management. The University of Georgia. A Guide to Corn Production in Georgia. CSS 01-2015. Barker, D. et al. 2005. Corn disease control. Ohio Agronomy Guide 14th Edition. Ohio State University Extension. Fernandez, F. 2009. Identifying nutrient deficiencies in corn. University of Illinois. Web sources verified 05/27/15. 140603060407