Introduction

Corn hybrid performance is annually evaluated in official hybrid trials (OHTs) by LSU AgCenter researchers to provide Louisiana growers, seedsmen, county agents and consultants with unbiased performance data for commercial corn hybrids submitted for evaluation by private companies. Selection of superior hybrids that are well adapted for a given region is essential for maximizing yield and profit.

Hybrid Selection

Hybrid selection is one of the most important decisions for producers, and there are many different hybrids available on the market. Soil conditions, irrigation practices and cultural practices vary among growers throughout the state; consequently, hybrid performance also varies based on soil type, irrigation, planting date, environmental conditions and location.

Grain yield is the primary trait considered by producers when selecting hybrids; however, maturity, stay-green, lodging, shuck cover, ear placement, disease and insect resistance also warrant consideration. Yield data from multiple locations can offer guidance as to hybrid performance consistency.

Hybrid maturity is categorized using relative maturity (RM) or growing degree day (GDD) rating systems. These two methods are based on the number of days or degree days required to reach physiological maturity. Louisiana producers grow early, mid- and full-season hybrids, with 112-day to 121-day hybrids producing optimal yield. Full-season hybrids do not consistently out-yield mid-season hybrids, and there is more variability in yield among hybrids within a given RM category than there is between maturity groups.

Hybrids that remain green later into their maturity usually retain better stalk strength and have less lodging potential. Shuck cover is important for protecting the ear and kernels from weathering and fungi. When planted late during the recommended window, hybrids will grow taller because of higher day and night temperatures and resulting internode elongation. Therefore, ear placement will be higher when compared to earlier planting dates, which may increase lodging potential. Consider planting a hybrid that has a low ear placement late during the planting season.

Corn hybrids have different insect and herbicide traits conferred by biotechnology and should be chosen based on the best fit for your production system. More information regarding available transgenic traits for insect and weed control are available in the LSU AgCenter’s Insect Pest Management Guide and Suggested Chemical Weed Control Guide.

To assist producers with hybrid selection, the LSU AgCenter conducts annual corn OHTs at several locations across the state, providing unbiased information on hybrid performance across different soil types and environmental conditions. In 2022, 45 hybrids were evaluated in the OHTs. Locations of these trials included the LSU AgCenter Dean Lee Research and Extension Center, Alexandria; LSU AgCenter Red River Research Station, Bossier City; LSU AgCenter Northeast Research Station, St. Joseph; and LSU AgCenter Macon Ridge Research Station, Winnsboro (Tables 4-9). Agronomic details for each location are included in Table 1. Selection criteria abbreviations and descriptions are defined in Table 2.

In addition to the OHTs, 16 on-farm core block demonstrations were conducted throughout the corn-growing areas of Louisiana by LSU AgCenter extension agents (Tables 10-26). This information should be used to supplement but not replace OHT results.

Procedures

The OHTs were conducted using a randomized complete block experimental design with four replications. Analyses of variance and least significant differences (LSD) were calculated only if differences existed at the 90% confidence level. If differences were significant, an LSD at the 10% probability level was calculated. If the LSD (0.10) for yield in a trial is 10 bushels per acre, there is a 10% chance that two hybrids with a reported yield difference of 10 bushels per acre are genetically equal and a 90% probability they have differences in genetic potential in that particular environment. LSD values are influenced by how well soil fertility, stand establishment, plot length, harvest efficiency and other variables are controlled and by the number of replications for each hybrid. The letters NS are used in the tables to indicate lack of significance (not significantly different) at the 10% probability level. The coefficient of variation (CV) reflects the magnitude of experimental error (random variation not accounted for by hybrids and replications) in relation to the trial mean. A high CV means that relative differences among hybrids were not consistent among replications, which reduces the precision of the test. Yield data for 2022 across locations as well as 2021 data for repeated hybrids is summarized in Table 3. Individual location summaries are located in Tables 4 through 9.

Planting Date

Corn growth and development responds to temperature and is not controlled by day length. Thus, the calendar date is not as important as soil and air temperature when considering optimum timing to plant corn. Good germination and emergence are expected when the soil temperature at a 2-inch depth is 55 degrees Fahrenheit by 9 a.m. for three consecutive days. This normally occurs in late February and March in Louisiana. In most years, the optimal planting window for south Louisiana is Feb. 23 to March 23, and for north Louisiana March 10 to April 10. Extending planting past the last optimal planting date can result in losses of half of a bushel to 1 bushel per day.

Frost may occur after these planting dates in some years; however, corn typically withstands frost with little economic injury. Corn younger than V6 (six-leaf stage) usually can withstand a light frost if the temperature does not drop below 30 degrees Fahrenheit. A moderate freeze will burn any existing leaves and cause them to drop, but new leaves can emerge in four to five days with warm temperatures. However, as the growing point moves upward near the soil surface, the possibility of injury increases.

Planting Rate and Depth

The optimal plant population for corn ranges from 27,000 to 30,000 live plants per acre. At 80% field emergence this would equate to planting 33,750 to 37,500 seeds per acre. The lower end of the recommended range should be used when lower yields are expected because of soil type, late planting date, drought-prone areas or low fertility. Higher populations should be used on highly productive deep alluvial soils or irrigated fields where moisture will not be a limiting factor.

Also, seeding densities can be affected by “ear flex.” Full-flex hybrids can compensate for fewer plants per acre because the ear grows both in length and girth. These hybrids usually produce only one ear per stalk. Individual semiflex hybrid ears will not compensate to the extent that full-flex hybrids will, but with low stand density and excellent growing conditions they may set two or more ears. Fixed-ear hybrids must obtain the desired population for maximum yield.

Seed size and shape are not critical for a good stand, but be sure to use the correct plate and planter for the size purchased. Corn should be planted 2 inches deep. It is vitally important to establish seed contact with moist soil, but planting seeds greater than 2 inches deep can increase the probability of an uneven plant stand, which can affect growth and yield.

Corn Growth and Development

Corn growth and development are closely related to temperature. Warmer temperatures result in rapid corn growth, and cooler temperatures result in slower corn development.

Temperatures are used to calculate growing degree days (GDD) or heat units (HU). Several formulas exist to calculate these GDD, but the one used most often is the modified 86/50 cutoff method (MGDD).

MGDD for any given day are calculated by subtracting 50 from the average daily temperature. The average daily temperature is calculated by adding the daily high and the daily low temperatures and then dividing by two.

GDD = Max. Temp + Min. Temp. – 50F

2

Two criteria or rules exist when calculating MGDD. First, if the daily high was greater than 86 degrees Fahrenheit, then 86 degrees Fahrenheit is used to calculate the average. Second, if the daily low was less than 50 degrees Fahrenheit, then 50 degrees Fahrenheit is used to calculate the average. These upper and lower temperature thresholds or limits define the boundaries beyond which corn develops very slowly, if at all.

Throughout the years, we have talked about the number of MGDD accumulated when silking or physiological maturity (black layer) occurs. For example, a particular hybrid will silk at 1,365 MGDD or reach physiological maturity at 2,800 MGDD.

Another useful purpose for following MGDD accumulation is to track the rate of leaf development prior to pollination. From V1 to V10, new leaves, which are defined by the appearance of leaf collars, emerge at a rate of about 85 MGDD per leaf. This is equivalent to about one leaf every five to six days in early April. From V10 to the final leaf, leaves emerge at a rate of about 50 MGDD per leaf.

Practical uses of this information include estimating how far along the corn crop should be for any given location if we know the planting date and the MGDD accumulations since the planting date. It is especially important to know the emergence date, but if this is not available, we can use 125 MGDD from planting to emergence.

For instance, corn should reach the V6 growth stage by the time 635 MGDD have accumulated since planting. This is calculated by using 125 MGDD from planting to emergence, then figuring 510 MGDD (6 multiplied by 85) from emergence to V6.

It is very important to remember that a shortage of MGDD resulting from early season cool temperatures can never be recovered. Midsummer days in the 90s do not necessarily accelerate MGDD accumulations because rate of growth is minimal when temperatures are above 86 degrees Fahrenheit.

Also, plant stress (soil compaction, excessive soil moisture, pest injury, hail damage) can interfere with this relationship and retard leaf development. Comparisons of predicted leaf development stages with actual leaf stages can, therefore, be used as an indicator of plant stress.

Fertility

Soil testing is the foundation of a sound fertility program and is necessary for maximum efficiency in applying correct rates of lime and fertilizer. Proper fertility is critical for optimizing crop yields, particularly in corn. Seldom is there a field that does not require the addition of fertilizer. The estimated uptake of nitrogen (N), phosphorus (P), potassium (K) and sulfur (S) by a 200-bushel-per-acre corn crop is presented in Table 27. Be aware that the values presented are not the amount of nutrients that need to be applied, but rather the total uptake by the corn crop from soil, fertilizer and other sources.

Soil pH

Soil pH affects the availability of nutrients to plant roots. The desirable soil pH for corn ranges from 5.8 to 7.0. Continued cultivation and the use of chemical fertilizers, especially those containing ammonium and sulfur, tend to decrease soil pH over time. Irrigation with water high in calcium carbonate, on the other hand, tends to increase soil pH.

Soil samples should be collected and checked for the degree of acidity or alkalinity. Lime is generally recommended at pH values below 6.1 (Table 28). Recommendations in Table 28 are general guidelines to raise pH. Soil texture and the buffer capacity of the soil are required for a more accurate estimate of the amount of lime that is needed. If lime is needed, it is recommended to apply it during the fall to provide enough time for it to react with the soil.

The relative neutralizing value (RNV) of lime impacts the amount that is needed to be applied. The RNV of a material is based on its fineness and calcium carbonate equivalent (CCE), or the amount of pure calcium carbonate to which the selected material corresponds, with finer materials reacting more quickly than coarse materials. An ag lime material with a CCE of 100 is “stronger” than an ag lime material with a CCE of 90. Consequently, less volume would be needed to increase the pH of a given soil.

Nitrogen

Nitrogen is necessary for chlorophyll synthesis and is part of the chlorophyll molecule involved in photosynthesis. Lack of N and chlorophyll means the crop will not utilize sunlight as an energy source to carry on essential functions, such as nutrient uptake. It is an essential component of amino acids, which form plant proteins. Therefore, N is directly responsible for increasing protein content.

A rough rule of thumb is to apply 1 to 1.2 pounds of actual N for each bushel of corn produced. Nitrogen should be applied according to whether the field is an alluvial plain, such as the Delta, or an upland soil and whether it is irrigated or dryland (Table 29).

Apply nitrogen in a split application with 50% to 75% applied before or at planting and the balance when corn is 3 to 12 inches tall. All the nitrogen can be applied pre-plant or at planting, but this increases the risk of fertilizer burn on seedlings and nitrogen loss from leaching or volatilization. An application of 20 to 50 pounds of nitrogen at tassel may be beneficial if environmental conditions result in leaching or volatilization of nitrogen.

Phosphorus

Phosphorus plays a role in photosynthesis, respiration, energy storage and transfer, cell division and cell enlargement in the plant. It promotes early root formation and growth, increases water use efficiency and hastens maturity.

Corn uses phosphorus early in its growth cycle, and it should be applied preplant or at planting (Table 30). Banding phosphorus will increase its efficiency when the soil pH is very acidic or alkaline or when soil test phosphorus levels are low. Also, starter fertilizers can be beneficial for soils that have a high pH or have very low to low phosphorus levels.

Soil testing is recommended to apply appropriate levels for each field, but in many soils 40 to 60 pounds of P₂O₅ per acre will be needed.

Potassium

Potassium is vital to photosynthesis. When K is deficient, photosynthesis declines and the plant’s respiration increases, which reduces the plant’s carbohydrate supply. Other functions of K include that it is essential for protein synthesis, helps control ionic balance and translocation of heavy metals, helps overcome the effects of disease, and is involved in the activation of 60 enzyme systems. Potash deficiency in corn results in reduced growth, delayed maturity and lodging.

Corn uses potassium early in its growth cycle and it should be applied pre-plant or at planting (Tables 31-34). Soil testing is recommended to apply appropriate levels for each field, but in many soils 40 to 60 pounds of K₂O per acre will be needed.

Sulfur

Sulfur is part of every living cell and is a constituent of two of the 21 amino acids that form proteins. Sulfur is often overlooked in a soil fertility program. With a reduction in sulfur emissions from industrial and transportation sources, atmospheric sulfur depositions are much lower; therefore, sulfur deficiencies in corn are becoming more common.

A typical 200-bushel-per-acre corn crop takes up about 30 pounds per acre with about 16 pounds per acre removed in the grain at harvest. When a soil test is utilized to determine if sulfur is needed, values of less than 12 ppm (Mehlich 3) generally suggest that additional sulfur may be needed. The typical recommended rate is 20 pounds of sulfur in the sulfate form per acre.

Zinc

Zinc was one of the first micronutrients recognized as essential for plants and the one most commonly limiting yields. Although it is required in small amounts, high yields are impossible without it. Corn is one of the most responsive crops to zinc applications.

If zinc is lower than 1 ppm, apply 10 pounds of zinc in a soluble form, such as zinc sulfate or zinc chelate, per acre (Table 35). Among the inorganic zinc sources on the market, the most common sources are sulfates, oxides and oxysulfates. Zinc sulfate and zinc chelates essentially are 100% water-soluble, while zinc oxides essentially are insoluble in a single crop season and are thus unavailable to the crop to be planted. Oxysulfates are a mixture of sulfates and oxides, with varying proportions of sulfates and oxides and different solubility levels (0.7% to 98.3%). The effectiveness of these can be highly variable, depending on solubility. Low solubility materials may have some value in a long-term buildup program, but when immediate results are the goal, highly soluble fertilizers are the best choices. For acceptable in-season efficacy, a zinc-fertilizer source should be at least 50% water-soluble. If a soil test shows zinc is between 1 and 2.25 ppm, apply 5 pounds of zinc per acre when broadcasting. Less is needed if using a banded application.

Seed Relabeling

Seed selection is one of the most critical decisions that farmers make each year. Seed is one of the largest expenses on the farm, and seed varieties differ greatly in both price and yield potential.

To make seed selection even more challenging, farmers also need to contend with a common practice in the seed industry where the same variety is sold under multiple brand names, which is referred to seed relabeling.

Seed relabeling creates two significant problems for farmers:

• Inconsistent seed pricing: Because different brands often sell the same variety for very different prices, producers may significantly overpay, perhaps not realizing that other brands sell the variety at a lower price.
• Lack of genetic diversity: When the same variety is sold under multiple brand names, it is easy for producers to unknowingly purchase the same variety from multiple brands while thinking they are buying a unique variety from each brand. This can lead to a failure to establish the genetic diversity that many farmers strive for when selecting the seed lineup.

Methodology: Decoding a seed tag

Federal and state seed labeling regulations typically require bags of seed to be labeled with the variety name. Relabeled seeds can be identified when you find the same variety marketed under multiple brand names.

Please see PDF for all tables.

Acknowledgements

LSU AgCenter Northeast Research Station

Matt Foster, Assistant Professor/Corn Specialist

Dennis Burns, Research Coordinator

Warren Ratcliff, Research Farm Manager

Theresa McLemore, Research Associate

Ashley Barfield, Research Associate

Riley Tullos, Research Associate

Melanie Netterville, Research Associate

LSU AgCenter Dean Lee Research and Extension Center

Daniel Stephenson, Professor/State Weed Specialist

Boyd Padgett, Professor/Plant Pathologist

Darrell Franks, Research Farm Manager

Fred Collins, Research Associate

Dalton Franks, Research Associate

Brandi Woolam, Research Associate

LSU AgCenter Macon Ridge Research Station

Rasel Parvej, Assistant Professor/Soil Fertility Specialist

Trey Price, Associate Professor/Plant Pathologist

Scott Washam, Research Farm Manager

Myra Purvis, Research Associate

Dustin Ezell, Research Associate

Jamil Uddin, Postdoctoral Researcher

LSU AgCenter Red River Research Station

William Waltman, Research Farm Manager

Rusty Anderson, Research Associate