Keeping a corn plant healthy and stress free during critical growth stages can help maximize yield potential. Understanding the significance of the growth stages and the effect of stress during any of the stages can help determine management decisions to improve overall plant health and protect yield potential.

Corn Yield Components

The number of ears per acre, the number of kernels per ear and the weight of each kernel determine corn yield potential. The interaction between factors such as genetics, weather conditions, soil types, pest pressure and available nutrients at a specific time in the growing season can affect corn yield potential.

Critical Growth Stages

It is important to understand the critical growth stages of corn that help determine final yield potential. Because corn does not have the ability to compensate for poor stands early in the season, establishing a uniform stand is the first step in optimizing yield potential.

The second critical growth stage occurs when the number of kernel rows per ear (during the rapid stage of corn vegetative growth – V5 to V8) and the number of potential kernels per row are determined¹. Stress-free corn plants during this time can help maximize the potential number of harvested kernels².

The third significant growth stage is the pollination process, which is critical to convert potential kernel numbers to actual developing kernels. The success of pollination is greatly influenced by the weather. Drought stress can desiccate silks and pollen grains, which results in barren ears and/or short ears with barren tips.

The grain fill or kernel development period is the final critical growth stage, which begins at pollination and ends at kernel black layer formation (or physiological maturity). Stress during this stage can reduce kernel number, size, and weight of harvested kernels².

Photosynthesis and Yield Potential

During the grain fill stage, any stress on the photosynthesis process can reduce yield potential. Photosynthesis produces the energy (carbohydrates) that a corn plant needs to survive and produce grain. Drought, high temperatures, foliar diseases, hail damage, and nitrogen deficiency can all significantly reduce photosynthesis³.

After pollination, corn plants redirect carbohydrate movement to fill the developing kernels, while sacrificing the health of the stalk, leaves, and roots³. This process can weaken the plant and make the plant more susceptible to stalk and root diseases. Fields at highest risk for stalk rot include those that have developed ears with high yield potential and have experienced severe stress during the grain fill stage.

The effects of plant stress can be intensified by sandy soils that have minimal water-holding capacity or on plants that have a restricted root system due to compacted soils, nematode damage or corn rootworm feeding.

Severe stress during the dough and dent stages of grain fill can lead to the premature formation of kernel black layer. This can reduce yield potential due to decreased kernel size and weight⁴. When the black layer forms, no additional nutrients can flow into the kernel and drydown begins.

A common photosynthetic stress that can occur during late grain fill is nitrogen deficiency, which can cause the leaves on the lower part of the plant to turn yellow and die. Saturated corn fields, due to wet conditions early in the season, may cause a loss of nitrogen from denitrification and leaching. Losing leaves during grain fill can reduce the plant’s ability to produce photosynthate and also decrease the nutrients that can be remobilized to the ear.

Managing Stress Conditions

While nothing can be done to control the stress damage from hail, drought and high temperatures, they can be mitigated with proper management and fertility. Adequate fertility is essential to maintain late-season plant health.

Weed Control

Weeds compete with crops for light, nutrients and water; especially during the first 3 to 5 weeks following emergence of the crop. It is important to control weeds in a corn field before they are 6 to 8 inches high, which is when they begin to impact corn yields. Late-season weed infestations do not reduce corn yield nearly as much as early weed competition; however, weeds at this time can harbor destructive insect pests such as thrips, which can vector Fusarium ear rot, and armyworms, which can defoliate corn.⁴

Herbicides reduce the early competition of weed infestations, reduce the seed bank and reduce the potential for competition in the following crop. Pre-plant, pre-emergent, or post-emergent herbicides are available that will selectively control most species of weeds in corn.⁵

Fungicide Applications

Finally, it is always important to scout fields and evaluate the potential for disease. The ear leaf and leaves immediately above and below the ear contribute over 75% of the plant’s carbohydrates; therefore, protecting these leaves is important. When foliar diseases are controlled, corn is also less susceptible to stalk rot pathogens.

The length of time foliar fungicides are typically active ranges from 14 to 21 days. The optimum application period accounts for the length of fungicide activity and protection of leaves during grain fill.

It is always best to look at multiple factors when deciding to spray a fungicide, including seed product disease ratings, yield environment, crop rotation and plant population. Fields planted as continuous corn would carry the most risk for disease pressure, due to corn stalk residue from the previous crop.

Proper management of your corn crop’s fertility and pests will increase yield potential and hedge the risk of weather stress. Contact your DEKALB^® Agronomist for recommendations and advice.