Genetic Diversity

    Genetic diversity means planting a portfolio of hybrids with a genetic makeup that includes as many of the different genetic families for making hybrids as possible. Genetic diversity increases the likelihood of growing consistent- yielding corn from one year to the next. The eight main genetic families used to develop hybrids are classified as Northern, Southern, Eastern, Western, Early Health, Late Health, High Yield and Flint. The genetic families originated with the first open pollinated corn varieties developed years ago. Farmers used the earliest method of plant breeding, called mass selection, to develop them. Each year, farmers saved the best ears for seed to plant next year’s crop. Genetics best for the particular locality were selected. For instance, farmers in Ohio and Indiana selected genetics that tolerate the saturated soils and diseases found in the high-rainfall, eastern Corn Belt. Corn plants needed thick rinds to make strong stalks providing stalk quality for severe stalk rot environments. Local farmers selecting for these traits developed the Eastern Genetic Family. Likewise, farmers selected the Northern Genetic Family for cool tolerance and the Southern Genetic Family for heat tolerance. The Western Genetic Family tolerates the drought conditions in the drier production areas of Nebraska and South Dakota. The high-yield environment of Iowa initiated the selection for maximum yield potential called the High Yield Genetic Family. The Early Health and Late Health Families added disease resistance which allowed hybrids to stay green and alive in the fall. Finally, Flints were used to add test weight and cool tolerance. The strengths and weaknesses of each genetic family are outlined in the table that follows this discussion. There are other genetic families not falling into the eight most frequently used categories. They are lumped into one classification that is called unrelated, as they are unrelated to the main eight families.
    Mass selection plant breeding methods used by early corn farmers were only partially effective because corn is cross-pollinated. The saved seed from corn plants having the largest ear received only half its genetics from that plant. The other half came from unidentified plants providing the pollen. With the development of the hybridization process, the genetics of both the female seed-bearing plant and male pollen source can be controlled. This enables plant breeders to combine several genetic families into one hybrid containing the strengths of each family. It provides the opportunity to correct weaknesses as well. For instance, the maximum genetic yield potential of the High Yield Family can be combined with disease tolerance and stalk quality genetics of the Eastern Family making high-yielding hybrids containing disease resistance and stalk quality. The High Yield Family crossed with the Northern Family develops high-yielding hybrids that tolerate cool weather. Through the development of the hybridization process, corn breeding became the art and science of developing parent lines and hybrids combining the strengths of different genetic families and minimizing the weaknesses.
    With hybrids being a combination of two parent lines, and with plant breeders frequently combining two genetic families into one parent line, hybrids can be a combination of more than two genetic types and can exhibit characteristics from all the types used. On the other hand, the parent line can be selected to exhibit a particular trait of one genetic type, with the remainder of the traits coming from the other genetic family, even though the parent line may be a combination of two families. In the descriptions of hybrids, genetic backgrounds are given in notation form. Capital letters indicate a strong percentage of a genetic family, small letters indicate a lesser contribution.
    When selecting corn hybrids, choose an assortment of genetic families to provide a hedge against different weather conditions. No genetic family is better than the others. Each has different strengths, weaknesses and weather preferences. Some tolerate cool, wet weather, others hot and dry. Each family has strengths and weaknesses regarding insect and disease tolerance, soil type adaptability, plant population preference, test weight, drydown, greensnap sensitivity and herbicide injury susceptibility.
    Genetic diversity increases the probability of achieving consistent corn yields. Planting one genetic type risks the entire crop if growing conditions expose a weakness. Knowing the genetic type helps in making management and placement decisions. For example, Eastern and Northern types can be planted on poorly drained fields, but Western types cannot. Southern types containing high-yield genetics respond to aggressive nitrogen rates. Northern types, with genes that code for enzyme systems that help promote efficient grain-filling during typical northern growing seasons, are recommended for cool wet localities. Your agronomist is a great resource who’s there to help you in making these crop management decisions.
    When planting Bt corn and selecting conventional corn hybrids for refuge acres, Western type genetics with high native tolerance to corn borer are preferred. On the other hand, Western types are therefore the least responsive to Bt technology. Southern types tolerate sand best with their large ear size and strong ear-flex, allowing for reduced plant population as a hedge against drought. Eastern types handle clay and saturated soils. This discussion continues later, but the point is, knowing the hybrid’s genetic type provides information to determine which hybrids work where and if genetic diversity is acceptable.
    The hybrid description and rating charts in this seed guide detail the genetic families used in making a hybrid. The first letter(s) of the genetic family is the designator (e.g., E = Eastern Genetic Family, HY= High Yield Genetic Family). A strong contribution of a genetic family to a hybrid is designated in upper case letters, while a smaller contribution is designated by lower case.

 

EASTERN GENETIC FAMILY		WESTERN GENETIC FAMILY
Strengths	Weaknesses	Strengths	Weaknesses
High Yield at High Population	Sensitivity to Heat	High Yield	Poor Rind Strength
Fast Silking	Sensitivity to Drought	Girthiness of Ear	Cool Weather During Grain-fill
Girthiness of Ear	Soft Kernel Texture	Strong Silking	Poor Roots
Disease Resistance	Poor Test Weight	Early Flowering Date	Tight Husk and Slow Drydown
Gray Leaf Spot Tolerance	Tight Silk Channel and	Strong Heat Tolerance	Weed Problems Due to
	Silkballing		Short Height
Staygreen	Sensitivity to Corn Borer	Excellent Drought Tolerance	Silkballing
Rind Strength for Stalk Quality	Lack of Ear Length	Strong Corn Borer Tolerance	Sensitive to Wet Soils
Loose Husk at Maturity	Eyespot	Thick Shank for Ear Retention	Poor Performance on Sand
Fast Drydown	Late Flowering	Strong Eyespot Tolerance	Sensitive to Low Potash
Strong Emergence	Poor Roots	Gray Leaf Spot Tolerance
Rapid Grain-Fill	Higher Ear Placement	Strong Response to Potash
Performance on Clay	Performance on Sand
SOUTHERN GENETIC FAMILY		HIGH YIELD FAMILY
Strengths	Weaknesses	Strengths	Weaknesses
High Yield	Poor Cold Tolerance	High Yield	Poor Cold Tolerance
Strong Heat Tolerance	Sensitivity to Corn Borer	Large Girthy Ear	Poor Seedling Vigor
Ear Length	Poor Disease Tolerance	Upright Leaf	Slow Silking
Tolerance to Low Population	Poor Stalk Quality	Strong Rind Strength	Late Flowering
High Test Weight	Poor Emergence		Poor Disease Resistance
Strong Performance on Sand	Late Flowering		Low Test Weight
Response to High Nitrogen	Slow Silking		Sensitive to Gray Leaf Spot
	Skinny Shank for Poor
	Ear Retention
	Sensitivity to Gray Leaf Spot
	Questionable Drought Tolerance
	Sensitivity to Low Nitrogen
	Sensitive to wet soils
NORTHERN GENETIC FAMILY
Strengths	Weaknesses
Earliness	Low Test Weight
Strong Cool Tolerance	Weak Early Season Growth
Rapid Grain-Fill	Sensitivity to High Heat
Strong Rind Strength	Herbicide Sensitivity
Strong Staygreen	Poor Roots
Excellent Eyespot Tolerance	Greensnap
Strong Germination	Poor Yield at Low Population
Strong Emergence	High Sensitivity to Gray
	Leaf Spot
Strong Silking
Loose Husk for Fast Drydown
Strong Performance on Sand
and Clay
Good Tolerance to Low Fertility

LATE HEALTH FAMILY		EARLY PLANT HEALTH
Strengths	Weaknesses	Strengths	Weaknesses
Ear Length	Sensitive to Corn Borer	Early Flowering	Sensitivity to Silkballing
Strong Disease Resistance	Low Yield	Cool Tolerance	Low Yield
Excellent Staygreen	Poor Rind Strength	Strong Seedling Vigor	Poor Roots
Wide, Dark Green Leaves	Rust Sensitivity	High Test Weight	Tillering
Rapid Early Season Growth	Greensnap Sensitivity	Strong Disease Resistance	Sensitive to Phenoxy
Test Weight	Sensitive to Smut	Excellent Staygreen	Herbicides
		Strong Rust Tolerance
		Tolerance to Gray Leaf Spot
		Adds Ear Length

Traits To Consider When Selecting A Corn Hybrid For A Particular Field

Seedling Vigor
Seedling vigor rating quantifies the ability of emerging corn seedlings to grow vigorously early in the growing season, especially if conditions are cool and wet. This is a function of environment and genetics. Certain hybrids are produced on female inbred lines possessing better genetics for making seed with increased seedling vigor. Seed produced during a year with favorable growing conditions has better seedling vigor. Seedling vigor is lost when the seed is exposed to frost or mechanical injury making seed coat cracks through which seed rot pathogens can enter. Use of Early Health and the Late Health Genetic Families increases the seedling vigor and early season growth of a hybrid. The Southern Genetic Family has the greatest challenge with emergence, but can compensate for reduced stands by forming larger ears on plants adjacent to areas where plants fail to emerge. Northern genetic types emerge well, but struggle with early season growth during cool weather. The affected seedlings exhibit purple stalks just above the soil surface caused by the failure to translocate sugars to the roots. The lack of early season growth in Northern types during cool weather predisposes them to herbicide injury, especially with growth-stimulating Phenoxy products such as Banvel. Being the most sensitive to herbicide injury, the Northern Genetic Family is the most responsive to herbicide tolerance systems such as Roundup Ready, LibertyLink, and Clearfield. The increased crop safety is of great benefit to the Northern Genetic Family. Another factor affecting seedling vigor is seed age. When seed is returned after the planting season, or when an overproduced hybrid is not sold, the carryover seed is reprocessed and sold the next year, providing the quality meets CROPLAN GENETICS standards. Seed corn carries over well. However, when the seed becomes old, seedling vigor is reduced, even when warm germination tests indicate it is legal to sell. In general, flat seed sizes retain seedling vigor better than rounds. This difference is not observed in new crop seed corn production, but shows up in carryover seed. CROPLAN GENETICS therefore recommends medium flat seed for no-till. Female inbred lines developed from the High Yield Genetic Family have softer kernel texture and produce seed that carries over from one year to the next better than seed produced from harder-grained Late Health and Early Health Families. The harder the seed coat, the better the test weight, but also the greater the surface cracks that may be incurred during harvesting and processing. Surface cracks allow the entry of pathogenic soil fungi which can kill the seed before emergence. In other words, improved seedling vigor but reduced test weight are opposite sides of the same coin.

Plant Population
Each hybrid has an optimal plant population at which it expresses its highest yield potential. The optimal plant population varies from one hybrid to another based on ear type. Consider ear type and its interaction with different corn production systems before making a hybrid selection.

Ear Type
  A hybrid has a fixed-ear type, a flex-ear type or somewhere in between. A fixed-ear hybrid makes the same size ear regardless of plant population. A flex-ear hybrid makes either longer or girthier ears when interplant competition is decreased by reducing population. Therefore, a flex-ear hybrid has a competitive advantage when plant populations are reduced by stress-related conditions such as: planting in cool, wet soils; emerging in no-till systems; and using lower populations as a drought control mechanism. The Southern Genetic Family has the greatest ability to flex its ear size at low populations developing ears that expand in length at reduced populations. Western and High Yield genetic types stretch in diameter by increasing kernel row number with decreasing populations. Eastern and Northern types make consistent ear size at high populations, but have little ability to increase ear size at low populations. Therefore, Northern and Eastern types require high populations to produce high yield. Conversely, Southern, Western, and High Yield types make higher yield at lower population by flexing ear size. There are situations when ability to yield at lower populations is strategic.

No-till: The stress of cooler soil temperatures and greater soil surface residues at emergence in no-till causes a loss in plant stand. Southern, Western, and High Yield type flex-ear hybrids react to lower populations by forming longer or girthier ears thereby retaining their yield potential.
Hedge against drought: Producers in the western Corn Belt using lower plant population as a hedge against drought, or producers farming sandier, drought-prone soil types, can benefit from flex-ear genetics that develop larger ears during above average rainfall seasons. Southern, Western, and High Yield flex-ear hybrids respond to lower populations by forming longer or girthier ears. However, as mentioned in the section on drought tolerance, other genetic families that have strong silking characteristics offer excellent drought tolerance without lowering population.
Continuous corn: Stalk quality is a problem in continuous corn with insects and diseases overwintering on the residue. Lowering the plant population reduces interplant competition by producing shorter, fatter stalks, lower ear placement and thicker stalk rind. These plant responses to population reduction improve stalk quality. The flex-ear type maintains high-end yield potential in spite of lower population. Therefore, reducing the plant population of Southern, Western and High Yield genetic types increases tolerance to continuous corn by improving stalk quality, yet retaining yield potential by flexing ear size.
 Low fertility soils: Flex-ear hybrids planted at low populations conserve the limited supply of soil nutrients for grain-fill. Fewer nutrients utilized in producing the vegetative part of the corn plant lowers the total nutrient requirement. Western and High Yield types planted at low populations outperform hybrids developed from other genetic families in fields with low fertility, especially low nitrogen. In the same way, the Western Genetic Family produces shorter plants that require fewer nutrients for development. Western Genetic type hybrids are therefore a key component of a high-acreage, low-input crop production strategy, especially now with herbicide tolerance systems that provide improved weed control in low leaf-area cropping systems. One outcome of increasing plant population is a reduction in stalk quality. Increasing plant population increases interplant competition. Corn plants respond to increasing competition by growing taller plants 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 Eastern types. With the advantages of flex-ear hybrids, why are fixed ear hybrids used? When planted at their optimal plant populations, fixed-ear hybrids, with their tolerance to high plant population, are the highest yielding. Northern and Eastern genetic types, found in most fixed-ear hybrids, have unusually strong silking characteristics and exceptional uniformity of ear size at high plant densities. Strong silking genetics are expressed by a hybrid prioritizing the movement of water directly to the silks at the time of pollination. Silks are over 90 percent water. Pushing silks out quickly ensures pollination and ear set, thereby driving yield. During years with favorable emergence and growing conditions, fixed-ear hybrids planted at high plant populations are the test plot winners. Fixed-ear hybrids tend to have shorter plant height. By increasing plant population, they grow taller. Taller plants increase yield potential by increasing leaf area. The high population production strategy increases yield to the point at which nutrient availability becomes limiting, necessitating higher fertility levels. If planted at too low a population, the reduced leaf area of the smaller plant wastes sunlight striking the soil surface. Planting fixed-ear hybrids at optimal plant population is essential to realize their high yield potential. Planting fixed-ear hybrids at high density requires the additional fertility to support the extra plants.

 Plant Growth Type Plant breeders follow two different strategies when developing high-yielding hybrids of a given maturity. They are 1) late tassel, short grain-fill and 2) early tassel, long grain-fill. With one, plant breeders select hybrids using longer periods of the growing season to build larger stature corn plants. This large plant tassels late, filling the grain rapidly with a large photosynthetic factory. This includes the Eastern, Southern, High Yield and Late Health genetic types. The opposite strategy selects hybrids that build smaller plants, tasseling early and using longer grain-filling periods to generate yield. Western, Northern, Early Health and Flint are this type. When planting late-maturing hybrids for the zone, or when planting is delayed by a wet spring, early tassel, long-fill types are more likely to mature and less likely to produce low test weight grain. When planting is early, or when planting an early maturing hybrid for the zone, the late tassel, fast-fill hybrid takes advantage of higher leaf area of larger corn plants

Stalk Quality Stalk quality is defined as the ability of the plant to stand intact through harvest after the grain-fill is completed and the plant is dead. Stalk quality is an issue in the eastern and southern United States where heat and high humidity breed leaf disease and stalk rot which cause 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. Lignin provides the rigidity that keeps the plant upright during the harvest season. Lignin is resistant to attack by the saprophytic soil-born 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 nutrients required for building thick rinds cannot contribute to yield. A side note: Corn silage produced using hybrids with thick rinds is low in feed quality because lignin is low in digestibility. For developing hybrids that have both high yield potential and acceptable stalk quality, plant breeders select genetics with late-season disease resistance that enable hybrids to stay green and alive until the grain-fill is completed. Hybrids that are green and alive in the fall are able to fight off stalk rot organisms that attack dead corn plants. Corn plants that stay alive in the fall, after grain-fill is complete, continue producing plant nutrients. With grain-fill complete, late-produced nutrients are sent to the pith, the inner tissue of the stalk, which adds support to the rind and assists in lodging resistance. The Eastern, Early Health and Late Health Genetic Families are the best sources of late-season plant health and staygreen stalk quality. Eastern, Northern, and High Yield Genetic Families are best sources of thick rind strength. Hybrids containing the Northern/Eastern combinations have the best total stalk quality. Southern and Western genetic types have little rind strength and poor staygreen, requiring complementary genetics in the hybrid that contribute staygreen or rind strength before attaining acceptable stalk quality. Placing Southern and Western genetics on well-drained soils with adequate fertility keeps them out of stalk rot-producing environments. Plant breeders create test plot-winning hybrids by selecting staygreen stalk quality that lasts through the harvest season without giving up yield. However, this strategy does not work in every situation. Staygreen fails to provide resistance to stalk rot when the corn plant is prematurely killed. For example, an early frost can kill the hybrid before it matures. Then stalk rot pathogens can attack the frozen and dead plant tissue. Hybrids with thick rinds provide the best stalk quality when stretching the maturity for the zone. Northern by High Yield genetic types work best in case of early frost or when heat units are below normal. However, during a cool season, some of these hybrids may run into test weight problems because they have a genetic predisposition for low test weight. Continuous corn is another challenge for staygreen hybrids. Diseases and insects overwinter on corn residue multiplying over years. When diseases and insects prematurely kill the plant, stalk quality suffers. Improve standability in continuous corn by planting hybrids that produce thick rinds, such as those developed from Northern and Eastern types. Another strategy for improving stalk quality in continuous corn is planting hybrids with increased ear-flex, allowing a reduction in plant population. Lower population promotes shorter plant height, increased rind thickness, and lower ear placement. Southern genetic types, planted at low population, work on continuous corn, but this type of hybrid also requires aggressive nitrogen. 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 hybrid is susceptible develop during the first year. At planting in the second year, every insect and disease to which that hybrid is susceptible is present in the field from day one. Early death, poor stalk quality, low grain yield and low test weight follow. Another limitation of staygreen occurs with low soil fertility. During grain-fill, high-yielding hybrids require a large supply of plant nutrients. If inadequate nutrients are available, cannibalization of lower leaves and stalk for nutrients occurs, and translocation of limiting nutrients to the grain results. If nitrogen is limiting, interveinal chlorosis is visible in nitrogen-starved plants. The movement of nitrogen from the stalk and leaves to the grain causes the early death of the corn plant. Stalk rot invades the dead plant causing it to fall down. It is critical that high-yielding hybrids, dependent on staygreen for stalk quality, be planted in fields with high fertility levels so nitrogen cannibalization and premature stalk death are avoided. This is especially true of Southern and Late Health genetic type hybrids. Careful field scouting during the fall can alert you to many stalk quality problems. Hybrids that stay green and alive 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 reddishpurple pigment. Fields with plants turning reddish-purple stand longer than fields dying quickly after black layer development.

Drydown
Drydown is defined as the rate at which moisture leaves the kernel after black layer. Factors influencing drydown include: husk looseness, test weight, and staygreen. Drydown is hastened in a hybrid with a husk that loosens early, allowing air to dry the grain. Northern and Eastern genetic types have looser husks. With husks loosening one week earlier in September, warmer grain-drying temperatures can make a dramatic difference in drying expense compared to mechanical grain drying. Drydown is slower in high test weight corn because it is more difficult for moisture to leave high density grain with harder seed coats. Northern, Eastern, and High Yield types have lower test weight grain and therefore faster rates of drydown. Low test weight and fast drydown frequently go hand in hand as does high test weight and slow drydown. Consider stalk quality and drydown together. Strong staygreen makes it possible to gain four weeks of stalk quality in exchange for giving up five days of grain drydown. This is a favorable cost/benefit proposition.

Test Weight
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 staying 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, Early Health, Late Health and Flint genetic types have the best test weight.

Yield And Hybrid Placement
Yield potential is extremely important in the production of profitable corn. However, in hybrid placement strategies, it must be considered along with stalk quality. Hybrids that deposit a larger percentage of sugars and starches into the grain have fewer nutrients remaining for rind and pith development. Conversely, hybrids with large stalks and thick rinds have fewer sugars and starches remaining to produce high grain yields. For this reason, plant breeders select high-yielding hybrids with enough stalk size and rind strength to produce acceptable stalk quality but rely on staygreen to keep the hybrid alive as long as possible. As mentioned in the section on stalk quality, staygreen is a good source of resistance to lodging, but has limitations with regard to continuous corn, low soil fertility and early frost potential. In these situations, it is wiser to plant hybrids with more rind strength and give up some yield.

Corn Borer Tolerance
Hybrids differ in tolerance to corn borer for several reasons. During reproduction, egg-laying moths are attracted to the largest corn plants. Hybrids containing genes from the Late Health genetic family have the characteristic of growing rapidly early in the season, making them especially attractive to egg-laying moths. Second generation corn borers prefer the latest planted, most immature corn. The Eastern genetic type takes the largest yield hit from second- generation corn borer because they flower late for their maturity and stay green late in the fall. For this reason, Eastern types provide the highest financial return on an investment in Bt technology. Southern type genetics have unusually skinny shanks that quickly break when invaded by corn borer causing dropped ears. Southern types have a strong response to Bt with a large reduction in dropped ears. Western genetics have the best native tolerance to corn borer with the fattest shank attachment aiding ear retention. They are the least responsive to Bt but are the best choice for refugee acres.

Drought Tolerance
Many hybrids are selected for strong drought tolerance even at high plant population. This is important in the western Corn Belt where low plant population is used as a hedge against drought. Low population strategy means using only flex-ear type hybrids that provide good yields at low plant populations: Southern, Western, and High Yield genetic types. Plant breeders have successfully selected for genetic sources of drought tolerance that allow the planting of higher yielding, fixed-ear hybrids in the western parts of Iowa, Minnesota and into the Dakotas and Nebraska. These hybrids prioritize moisture movement to the silks at pollination, allowing for silking that is synchronized with pollen shed. They are more likely to form ears during hot, dry weather because they start with a well-pollinated ear. Eastern, Northern and Western genetic types have strong silking genetics. In the western drought-prone areas of South Dakota and Nebraska, the Western genetic type silks strongly and performs especially well. It tolerates both heat and drought, and has a large flex ear that keeps yield potential high at moderate population. Southern genetic types are the slowest silking during dry weather. Therefore, they should be planted at lower populations in drought-prone areas to conserve moisture for the pollination period. Southern types are the first to show unpollinated tips when stressed during the flowering stage of development due to longer ears and higher moisture requirements for silk development. By selecting hybrids that tassel and silk in synchrony, even when it is dry, strong drought tolerance is obtained without having to reduce population. This is a major accomplishment by plant breeders in the quest for higher yielding, more stress-tolerant hybrids.

Soil Types
Proper hybrid selection for a particular field cannot be made without considering soil type. When planting on heavy clay soils in high rainfall areas, saturated soil conditions, such as those found in northwest Ohio and eastern Wisconsin, are often a problem. Northern and Eastern genetic types show the highest tolerance to wet feet, whereas Western and Southern types perform poorly when soils are saturated. Corn growth and development slows down on heavy soil types. Corn maturities need to be conservative on these soils. On lighter soil types more prone to drought, large ear types, such as Southern by High Yield and Northern by High Yield, do well, whereas Eastern types do poorly. Corn growth and development speeds up on sandy soil types. Western types perform poorly on saturated soils because they are sensitive to wet feet. In addition, Western type hybrids tend to be short, and moisture stress on sandy soils develops a plant with too low an ear and too thin a leaf canopy that can lead to weed control challenges. As a whole, most Western style hybrids prefer the well-drained silt loam type soils, though they do well on clay loams if tiled and not saturated.

Fertility Levels
Southern type hybrids are nitrogen-driven. If the goal is winning a yield trial, a Southern style hybrid placed on a well-drained, high-fertility field with an aggressive nitrogen program is the winning package. Eastern type genetics planted at aggressive plant population are the next choice. Western Genetic types are tolerant to lower nitrogen when populations are adjusted down, but are sensitive to low potassium and respond to high potassium. Western genetics do well where native soil potassium levels are high. In fact, high potassium levels in the plant drive drought tolerance in Western types. Potassium is important in plant water management because it regulates the opening and closing of stomates. The Northern by High Yield genetic type is tolerant to low fertility because it flexes its ear, allowing for a reduction in plant population. The robust plant type of Late Health genetics responds well to the higher fertility levels required for making the larger photosynthetic factory.

Herbicide Tolerance
There are many conventional herbicide products on the market that perform well and have acceptable crop tolerance. However, herbicide tolerant genes add value in several special cases. The Northern genetic family has difficulty establishing roots in cool soils. When stressed by cool weather, Northern types struggle to translocate sugars to the roots causing a purple coloration of the stalk above the soil surface. The sugars are required for generating new root growth. If sprayed with many herbicides at this stage, injury can occur. Northern and Early Health types are sensitive to growthstimulant herbicides. These two genetic types are combined together in many of the hybrids popular in northern areas. For this reason, Roundup Ready, Clearfield, and LibertyLink systems add value, because crop safety is enhanced in genetic backgrounds having this sensitivity. This is critical in northern areas where spraying under less than optimal conditions frequently occurs due to cool, wet weather. Western genetics are short in plant height causing a problem in the western Corn Belt where lower plant populations are used. Decreasing population decreases interplant competition and overall plant height. With the reduction in leaf area comes a reduction in soil surface shading. This lack of competition by the crop for sunlight increases weed pressure. Roundup Ready, Clearfield, and Liberty- Link production systems offer total postemergence weed control solutions for late-season weed problems. Genetic herbicide tolerance also has a special application for no-till. With no soil tillage, Roundup Ready, Clearfield, and Liberty Link production systems offer total postemergence weed control solutions superior to most conventional preplant systems. When combined with the right no-till genetics, herbicide-tolerant gene systems enhance no-till. With increasing fuel prices, the economics of no-till increase simultaneously.

Maturity
In the past, planting an earlier maturing hybrid meant sacrificing high-end yield potential. However, plant breeders are increasing the yield potential of all maturities. Maximum yield now is obtained by selecting the proper maturity for the zone where planted. The best maturity for any zone, in any year, maximizes the available growing season. July, August, and the first half of September have daylength, sunlight, and heat units ideal for grain-fill. A hybrid black layering between September 15th and 20th maximizes the grain-fill period with time remaining for grain drydown. Although it may be tempting to plant a maturity adapted to an earlier or later zone, grain-fill, yield and stalk quality are sacrificed. An earlier hybrid sacrifices yield as grain-fill is completed while other hybrids are still filling grain. The selection of later maturing hybrids sacrifices both yield and drydown. Yields are reduced as daylight grows shorter and heat units per day decrease during the later stages of grain-fill. Drydown is sacrificed with the hybrid finishing during the latter days of September and early October. Observed maturities are strongly influenced by weather and will display "normal" variation from year to year. It makes no sense stretching maturity to get more yield, and it makes no sense sacrificing yield to an earlier hybrid. Select maturity adapted to the zone where it is planted.

"Team No-Till"
Selecting hybrids for no-till requires special attention, because residue and lack of tillage slow warming and drying of soil. Seedling vigor is a hybrid characteristic that takes on greater importance in no-till. As seed ages into its second and third year, medium flats retain seedling vigor better than other grade sizes. Therefore, we recommend medium flat seed for no-till, because age of seed is unknown by the producer. Delayed emergence from cooler, wetter, no-till soils delays maturity. Therefore, mid-season maturing hybrids for no-till are encouraged over full-season. Cooler seedbeds and poorer soil-to-seed contact causes thinner plant population in no-till. Flex-ear hybrids are therefore recommended over fixed-ear hybrids. Crop residue carries many corn diseases and insects to the next crop. Therefore, the increased residue found in no-till settings increases disease and insect pressure. Hybrids with strong leaf disease resistance and staygreen are required to fight off leaf diseases. Thick rinds provide stalk quality if hybrids are killed prematurely by disease. With the lack of tillage, weed control is challenging in no-till. Roundup Ready, Clearfield, and LibertyLink production systems offer total postemergence weed control solutions superior to most conventional systems. In combination with the right genetics, this offers another tool for no-till. In summary, the perfect no-till hybrid is one combining the following characteristics: strong seedling vigor, flexear, leaf disease resistance, staygreen, rind strength, and herbicide tolerance.