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Planning, planting for top corn yields

Successful corn production requires optimum planting performance and substantial preparation. My college crop science professor often said, “Ninety percent of producing a good corn crop is accomplished when you pull out of the field with the planter.”

Although high-yielding corn certainly requires field scouting and management inputs during the season, problems created by poor planting cannot be corrected during the season.

The planting process and preplanting decisions — including hybrid choice, seeding rate, seed placement, and planting date — determine many important factors which influence yield.

Herbicide-resistant hybrids have not captured nearly as much market share in corn production as they have in cotton and soybean production. This is largely because most herbicide-resistant corn systems cost as much as or more than conventional corn weed control systems.

Herbicide-resistant hybrid choices are rather limited and yield performance compared to conventional hybrids is often questioned as well.

Furthermore, the StarLink fiasco highlights the need to address marketability of GMO products, particularly those not approved for all markets.

Mississippi State University research studies comparing transgenic hybrids to their conventional isolines indicate corn grain yields may often differ, even though hybrids have genetically similar backgrounds. This suggests bio-engineering may affect hybrid performance. Thus, producers should not assume transgenic corn hybrids will always perform as well as or better than their closely-related conventional isolines.

Growers can plant no more than 50 percent of their corn acreage in Bt hybrids trademarked YieldGard, which contain the MON-810 insertion event. Growers are required to sign an agreement to plant non-Bt corn as a refuge within a half mile of the Bt corn. Neighbors' conventional corn does not count as refuge. The non-Bt refuge may be treated with insecticides (excluding sprayable Bt products) as needed.

Bt corn effectively controls both Southwestern and European corn borers and has moderate control on corn earworms and fall armyworms. However, Bt corn does not control the primary insect pests during stand establishment, such as chinch bugs, cutworms, rootworms, and wireworms. Thus, using a Bt hybrid will not substitute for the use of a soil-applied insecticide at planting.

Mississippi State University research suggests the inclusion of a Bt event does not increase hybrid yield potential over a closely-related conventional isoline in the absence of corn borers. Thus, a grower will not likely recover the higher seed cost of the Bt technology unless significant corn borer infestation is likely. Unfortunately, seasonal corn borer populations are not very predictable and crop rotation has little effect, since corn borers are relatively mobile.

Local historical infestation levels and planting dates should be used to justify the use of a Bt hybrid.

Late-planted corn is more likely to benefit from Bt inclusion because second- and third-generation borers are more attracted to lush, green, young corn.

Growers should strive for 18,000 to 32,000 plants per acre, the exact number depending mainly upon a field's yield potential, planter row width and planting date. If a corn yield goal of 150 bushels per acre (45 bushels per acre for soybeans or 2 bale per acre for cotton) is realistic, particularly under irrigation, then strive for 26,000 to 32,000 plants per acre. If this goal is unrealistic, then lower the seeding rate accordingly.

Planter row width changes optimum plant population because it affects plant spacing. Seeds spaced closer than 6 inches apart normally increase competition for light, water and nutrients, which weakens stalk quality without increasing yield potential, particularly under stress. I recommend planting 2,000 to 4,000 fewer seeds per acre with wide-row planters than you would plant with 30-inch row-width planters.

Overplant the desired plant population about 5 to 10 percent, the exact amount depending upon seed germination and planting conditions. Early-planted corn (soil temperatures of 50 to 55 degrees F) should be seeded slightly thicker than normal because cool spring conditions cause higher seedling mortality and shorter plants at tassel, meaning more plants are needed to intercept light. Conversely, growers should lower seeding rates when they are planting late, since warm soils enhance seedling establishment, taller plants are produced and yield potential decreases.

Poor corn seed spacing and depth uniformity may affect yield potential as much as plant population. Research indicates that most growers could improve corn yields 5 to 15 bushels per acre just by improving planter performance. Best of all, it will not cost you a dime to gain this improvement.

One common cause of seed distribution problems is excessive planter speed. The optimum speed for plate-type planters is 4 to 4.5 mph; for vacuum-type planters it is 4.5 to 5 mph. Exceeding those speeds contributes to poorer seed spacing and depth uniformity, largely because seeds roll and bounce in the seed furrow.

Poor seeding uniformity reduces yield potential because corn has a determinate growth habit and does not tiller or produce branches to alter plant size.

Crowded and late-emerging plants produce small ears and spindly stalks due to excessive competition for light, water and nutrients.

Corn seed is available in numerous combinations of size and shape, which may further aggravate planting problems. Growers should thoroughly check planter performance — just because something worked last year, doesn't necessarily mean it will this year.

Many producers plant corn too shallow. Corn seed should be planted 1.5 to 2 inches deep to insure normal root development. Planting depth should be set in the field during planting, because soil type, seedbed condition and moisture may influence actual depth. Corn seed's inherent energy and germination process insure emergence from depths as great as 3 inches.

The origination point of the nodal root system is moved upward when corn seed is not planted deep enough. Corn seed placed less than 1 inch deep will develop nodal roots at or above the soil surface. This exposes these roots to factors capable of impeding root development, such as hot dry soil, herbicide injury, and insect predation. This often leads to stand problems, nutrient deficiencies and even drought stress throughout the year. Birds are also more likely to cause stand loss of shallow-planted seed.

Erick Larson is a grain crops specialist with Mississippi State University. e-mail:

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