Corn Production Guide – Index

A-1130, May 1997

Hybrid Corn Selection

One of the most important management decisions a corn grower makes each year is the selection of corn hybrids for spring planting. During the past 50 years there has been a continuous improvement in the genetics of corn hybrids. These improvements have greatly contributed to steady increases in grain yield potential ranging from 0.5 to 2.0% per year. To stay competitive growers should introduce new hybrids to their planted acreage on a regular basis.

Growers should select hybrids best suited to their farm operation. Size of corn acreage, soil type, tillage practices, pest problems and desired harvest moisture determine needs for such traits as drydown, disease resistance, insect tolerance, early plant vigor, plant height and relative maturity.

End use of corn should always be considered: is corn to be used for grain or silage? Is it going to be utilized for wet milling? Is it to be sold directly to the elevator or the wet milling plant, or primarily used on the farm to feed livestock? Capacity to harvest, dry and store grain corn also needs consideration.

The key factors to use in choosing corn hybrids are:

• Maturity–Select hybrids with maturity ratings appropriate for your geographic area or circumstances.
• Yield–Select hybrids with consistently high yields across a number of locations or for two years.
• Standability–Use hybrids that stand well throughout the season with tolerance to stalk rots and green snap.
• Disease resistance or tolerance–Grow hybrids with tolerance/or resistance to stalk rots, foliar diseases and ear rots.
• Seed quality–Plant only high quality seed and seed sized to match your planters capabilities.
• Drydown rate–Choose hybrids that drydown rapidly or lose kernel moisture while in the field.
• End use–Choose hybrids which best fit the final utilization needs; wet milling, feeding, silage, waxy corn or others.

Growing Degree Days and Corn Maturity

"Growing-degree days" (GDD) or heat units has been developed to more accurately rate corn maturity. It is based on the number of growing degree days between emergence date and physiologic maturity of a hybrid (Table 1). Growing degree days vary in North Dakota from 2400 GDDs in southeastern areas to 1900 GDDs in the northern areas (Table 2).

In calculating growing degree days (GDD), temperatures from a lower limit of 50�F and an upper limit of 86�F are accumulated for the growing season by applying the following formula to each day's maximum and minimum temperatures.

      (Max. Temp. + Min. Temp.)
GDD = -------------------------  –50
                  2 

Maximum temperatures higher than 86�F are entered as 86 and temperatures below 50� F are entered as 50 in the formula. GDDs are accumulated from seedling emergence until physiological maturity. Kernel moisture content at physiological maturity generally averages about 34%. At physiological maturity a "black layer" will form under the outer layer of the kernel tip. When this forms it signals that kernel dry matter accumulation has reached the maximum level. Corn will not be hurt by frost after that point. Hybrids may vary up to 10% in kernel moisture at physiological maturity.

Corn Growth Stages and Development

The corn staging system divides development into vegetative (V) and reproductive (R) stages (Table 3). Sub-divisions of the V stages are designated numerically as V1, V2, V3, etc. through V(n), where (n) represents the last leaf stage before VT for the specific hybrid under consideration. The first and last V stages are designated as VE (emergence) and VT (tasseling). The (n) will fluctuate with hybrid and environmental differences. The six subdivisions of the reproductive (R) stages are designated numerically with their common names.

Planting Dates

Higher corn grain yields will be obtained with early plantings. In most regions this means seeding between the last week of April and May 15. Early planting is recommended because risk of fall frost damage is greater with each day planting is delayed. The risk increases rapidly after May 20 and seeding corn for grain production is not recommended after June 1. Select and plant early-maturing, short-season hybrids when planting is delayed because of wet, cold planting conditions. Date of planting studies have been conducted at Oakes, Casselton and Fargo, ND. In these studies approximately one bushel per day was lost by delay of planting during the month of May. For silage corn, later plantings can be tolerated without great yield losses but can result in frosted corn, thus lowering quality of forage.

Plant Population

Hybrids react differently to various plant populations, and producers should consult with their seed dealer on recommendations. Plant populations should be based on available moisture, potential rainfall during the growing season, and soil type. Populations of 14,000 to 18,000 plants per acre are recommended in western low rainfall areas and on light sandy soils. Populations of 22,000 to 28,000 plants per acre in eastern, high rainfall areas and 28,000-32,000 plants per acre for corn grown under irrigation are recommended for plant population at harvest. The seeding rate should be 10-15% higher than the desired harvest populations.

Rotations and Corn

Crop rotations and crop sequences are management tools that can be used to exploit available resources more efficiently. Evaluation of cropping systems is complex with rotations and crop sequences only one part of the system. Research on corn rotations usually compares monocropping (continuous corn) to various other cropping sequences with some legume crop or small grain. Biological systems research usually shows an advantage to rotation of crop species. The factors involved include but not limited to are: soil fertility, water use, soil tilth, soil erosion, crop residues, weed control, insect control and disease.

Differences between continuous corn and rotational corn yields are greatly reduced as N rates are increased to attain maximum yield productivity in non-legume cropping sequences. However in many rotations, the difference in yields can’t be made up by N application alone. Factors which causes these additional rotational benefits include reduced disease problems, less insect pressure, improved soil physical properties, elimination of phytotoxic substances in corn residues and the addition of growth promoting substances in legume residues.

One exception to the advantage of using legumes in a corn rotation can occur in years when a perennial legume such as alfalfa can deplete soil moisture during the fall, prior to spring corn planting. Disease pathogen populations can be reduced or suppressed by rotations to certain broadleaf or legume crops. The key function of a rotation with corn is not to eradicate the pathogen but to reduce it to a low enough level so a profitable yield can be produced when the susceptible crop (corn) is replanted into the crop sequence at a later time.

A mystery does remain, however, in that most research data show higher corn yields using rotations even when all factors known such as fertility, pest pressures, water available, and hybrids are equal. Yield benefits have been obtained by rotating to legumes, from non-row crop to corn, from row-crop to corn, and even from one hybrid to another hybrid the second year in a sequence. In a recent national survey, corn yield increases due to rotations ranged from 6 to 30 bushels per acre. The best recommendation is to rotate, rotate, rotate.

Weed Control

The weed control suggestions in this production guide are based on the assumption that all herbicides mentioned will have a registered label with the Environmental Protection Agency. Corn treated with with a non-registered herbicide may have an illegal residue which, if detected, could cause condemnation of the crop. Nonregistered herbicide use is illegal and a user could be subject to a heavy fine even without detectable residue.

Chemical Weed Control for Corn

Roundup Ultra/RT, Glyphos (glyphosate)

        Rate: 0.5 to 2 pt of a 3 lb ae/gal conc. (0.19 to 0.75)
       Weeds: Emerged grass and broadleaf weeds.
       Apply: Preplant or anytime prior to crop emergence.
     Remarks: A nonselective, translocated, foliar herbicide. No
              soil activity. Refer to label for adjuvant use.
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Gramoxone Extra (paraquat) RUP

        Rate: 1.5 to 3 pt (0.47 to 0.94)
       Weeds: Emerged annual grass and broadleaf weeds.
       Apply: Preplant or anytime prior to crop emergence.
       Apply: A nonselective, foliar herbicide. No soil activity.
              Apply with a NIS at 0.12 to 0.25% v/v. Good plant
              coverage is essential.
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Eradicane (EPTC & safener)

        Rate: 4.75 to 7 pt, 16 to 24 lb 25G (4 to 6)
       Weeds: Grass and some broadleaf weeds.
       Apply: PPI
     Remarks: Immediate incorporation is required for best results.
              Use high rate for wild-proso millet control. Weak on
              wild mustard.
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DoublePlay (EPTC + acetochlor + safener) RUP

        Rate: 4.5 to 8 pt/A (3.15 to 5.6 + 0.78 to 1.4)
       Weeds: Most annual grass and some broadleaf weeds.
       Apply: PPI
     Remarks: Immediate incorporation is required using water as
              spray solution. Incorporation can be delayed up to
              4 hours if using liquid fertilizer as carrier or up
              to 1 day if impregnated on dry bulk fertilizer.
              Partial control of volunteer grains, wild-proso
              millet, and field sandbur at 5 to 7 pt/A.
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Lasso (alachlor) RUP

        Rate: 2 to 3.5 qt 4EC/MT, 3 to 5.3 lb 65WDG,
              13 to 26 lb 15G (2 to 3.5)
       Weeds: Grass and some broadleaf weeds.
       Apply: PPI, PRE or EPOST: Up to 5 inches tall.
     Remarks: Weak on wild mustard. Less effective PRE than Ramrod
              on many soils. PPI gives more consistent weed control.
              EPOST is for reduced competition of labeled weeds.
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Dual (metolachlor)

        Rate: 1.5 to 3 pt, 6 to 12 lb IIG/25G (1.5 to 3)
       Weeds: Grass and some broadleaf weeds.
       Apply: PPI or PRE. Fall: After Oct 15 but before
              ground freezes.
     Remarks: Weak on wild mustard. Less effective PRE than Ramrod on
              many soils. PPI gives more consistent weed control.
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Frontier (dimethenamid)

        Rate: 13 to 25 fl oz (0.76 to 1.46)
       Weeds: Grass and some broadleaf weeds.
       Apply: EPP, PPI or PRE
     Remarks: Use rate based on CEC or soil texture and OM. Frontier
              has provided equal grass control compared to Lasso or
              Dual.
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Harness (acetochlor + safener) RUP

        Rate: 1.25 to 3 pt (1.1 to 2.6)
       Weeds: Grass and some broadleaf weeds.
       Apply: PPI or PRE
     Remarks: Harness has provided equal or greater weed control
              compared to Lasso, Dual or Frontier.
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TopNotch (microencapsulated acetochlor + safener) RUP

        Rate: 4 to 7.25 pt (1.6 to 2.9)
       Weeds: Grass and some broadleaf weeds.
       Apply: Reduced or No-till: EPP and PRE
     Remarks: May be tank-mixed with Gramoxone Extra or Roundup
              Ultra/RT for EPP. Can be tank-mixed with Atrazine,
              Bladex or Banvel for PPI or PRE applications in
              conventional till systems. Refer to label for rates
              based on soil texture and interval between application
              and planting.
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Surpass (acetochlor + safener) RUP

        Rate: 1.5 to 3.75 pt, 6 to 15 20G
  Early POST: 1.2 to 3 pt (1.2 to 3)
       Weeds: Grass and some broadleaf weeds.
       Apply: PPI, PRE and EPOST
     Remarks: Surpass has provided equal or greater weed control
              compared to Lasso, Dual or Frontier.
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Ramrod (propachlor)

        Rate: 4 to 6 qt, 20 to 30 lb 20G (4 to 6)
       Weeds: Grass and some broadleaf weeds.
       Apply: PRE
     Remarks: Weak on wild mustard. More effective PRE than Lasso
              or Dual in North Dakota. PPI decreases control.
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Prowl (pendimethalin)

        Rate: 2.4 to 4.8 pt EC, 1.67 to 3.33 lb DG (1 to 2)
       Weeds: Grass and some broadleaf weeds.
       Apply: PRE
     Remarks: DO NOT INCORPORATE. Do not use on sands or loamy
              sands. Use the high rate on fine textured soils high
              in OM.
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Atrazine RUP

        Rate: 1 to 2 lb ai/A
       Weeds: Broadleaf and some grass weeds.
       Apply: PPI and PRE: Spring only.
     Remarks: Use higher rate on fine-textured soils. Soil residue
              may injure some crops planted the following year.
              Consult label for crop rotation restrictions.
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Bladex (cyanazine) RUP

        Rate: 1.3 to 5.3 lb 90DF (1.2 to 4.75)
       Weeds: Broadleaf and some grass weeds.
       Apply: PPI and PRE
     Remarks: Soil residues unlikely the year after application.
              Weak on redroot pigweed. Use higher rates on 
              fine-textured, high OM soil. Do not use on sands,
              loamy sands or soil with less than 1% OM.
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Broadstrike + Dual (flumetsulam + metolachlor)

        Rate: 1.75 to 2.75 pt (0.04 to 0.0625 + 1.6 to 2.33)
       Weeds: Most grass and broadleaf weeds.
       Apply: EPP, PPI or PRE
     Remarks: EPP may be made up to 30 days before planting.
              Preplant incorporate into the top 2 inches of soil.
              Use low rate on coarse textured, low OM soils and
              the high rate on fine soils with >3% OM or applied EPP.
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Hornet (flumetsulam + clopyralid)

        Rate: 0.2 to 0.3 lb DF (0.64 to 1 oz + 2 to 3 oz)
       Weeds: Broadleaf weeds
       Apply: EPP, PPI or PRE
     Remarks: Early preplant (EPP) may be made up to 30 days before
              planting. Preplant incorporate into the top 2 to 3
              inches of soil. Use low rate on coarse textured, low
              OM soils and the high rate on fine soils with >3% OM
              or applied EPP.
----------------------------------------------------------------------

Hornet (flumetsulan + clopyralid)

        Rate: 1.6 to 4.8 oz DF (0.4 to 1.12 + 1 to 2 oz)
       Weeds: Broadleaf weeds
       Apply: POST: Corn up to 24 inches tall.
     Remarks: Apply to broadleaf weeds less than 8 inches tall.
              Use NIS at 0.25% v/v or PO at 1% v/v. Use 28% UAN at
              2.5% v/v/ during dry conditions. Do not cultivate
              within 10 days before or after application. Refer to
              label for rate range for various weeds. Apply with
              Stinger at 2.67 fl oz/A for improved Canada thistle
              control. Do not exceed 0.07 lb ai/A flumetsulam
              per year.
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Shotgun (atrazine + 2,4-D) RUP

        Rate: 2 to 3 pt (0.56 to 0.84 + 0.25 to 0.375)
       Weeds: Broadleaf and some grass weeds.
       Apply: Preplant, PRE or EPOST
     Remarks: Lower atrazine rates reduce potential for carryover. Do
              not use on coarse textured soils with less than 1% OM.
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Atrazine + oil additive RUP

        Rate: Appropriate rate + oil additive (1 to 2 lb ai/A)
       Weeds: Broadleaf weeds and some grasses.
       Apply: POST: Weeds less than 1.5 inches tall.
     Remarks: Apply before corn is 12 inches tall. Apply with an
              oil additive at 1 qt/A. Provides partial control of
              foxtail. Atrazine soil residue may injure subsequent
              crops.
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Bladex (cyanazine) + NIS or vegetable oil additive RUP

        Rate: 1.3 to 2.2 lb 90DF (1.2 to 2.0)
       Weeds: Grass and some broadleaf weeds.
       Apply: POST: Weeds less than 1.5 inches.
              Corn up to 4-leaf stage.
     Remarks: Do not use petroleum based crop oils. Vegetable oil
              additive increases weed control and risk of crop
              damage compared to NIS. Use only 90DF for POST
              applications. Avoid application under cool, wet
              conditions.
----------------------------------------------------------------------

Banvel, Clarity (dicamba)

        Rate: 0.5 to 1 pt of a 4 lb/gal conc. (0.25 to 0.5)
       Weeds: Broadleaf weeds.
       Apply: EPOST: Corn from spike to 8 inches tall.
     Remarks: Do not apply Clarity after corn is 8 inches tall.
              Apply Banvel with drop nozzles after corn is 8 inches
              tall to increase crop safety and reduce drift. Use
              low rate on coarse textured or low OM soil Can be
              applied with Accent for grass control.
             ---------------------------------------------------------
        Rate: 0.5 pt of a 4 lb/gal conc. (0.25)
       Weeds: Broadleaf weeds.
       Apply: POST Directed: Corn at 8 to 36 inches or 15 days prior
              to tassel.
----------------------------------------------------------------------

2,4-D

        Rate: 0.5 to 1 pt of a 4 lb/gal conc. (0.25 to 0.5)
       Weeds: Broadleaf weeds.
       Apply: POST and POST Directed:
              Corn from 3-leaf to 30 inches tall.
     Remarks: Use drop nozzles when corn is over 8 inches tall but
              before tasseling.
----------------------------------------------------------------------

Buctril, Buctril Gel (bromoxynil)

        Rate: 1 to 1.5 pt EC, 3.33 to 5 A/pack (0.25 to 0.37)
       Weeds: Most annual broadleaf weeds.
       Apply: POST: Corn prior to tasseling.
     Remarks: Apply to weeds in the seedling stage. Weak on wild
              mustard. Could be used when drift of dicamba or 2,4-D
              may injure susceptible broadleaf crops.
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Basagran (bentazon)

        Rate: 1.5 to 2 pt 4S (0.75 to 1)
       Weeds: Wild mustard, cocklebur, Canada thistle, and sunflower.
       Apply: POST: Mustard: 4 to 6 leaf. Thistle: 6 to 8 inches.
     Remarks: Could be used when drift of Banvel/Clarity or 2,4-D
              may injure sensitive crops. Thorough coverage is
              essential. Avoid application to stressed plants. Split
              applications needed for Canada thistle control.
----------------------------------------------------------------------

Sencor (metribuzin) + broadleaf herbicide

        Rate: 1.6 to 2 oz 75DF, 2.4 to 3 fl oz 4F + rate of
              broadleaf herbicide (0.075 to 0.09 + labeled rate)
       Weeds: Most broadleaf weeds.
       Apply: POST: Prior to tassel but MUST also follow crop stage
              restrictions of tankmix broadleaf herbicide.
     Remarks: Tankmix with Atrazine, Basagran, Laddok, Buctril,
              Banvel, Clarity, Marksman, or 2,4-D. Do not use oil
              additive with any tankmix. Refer to label for adjuvant
              use with each broadleaf herbicide tankmix. Do not
              apply more than 5 oz 75DF per season.
----------------------------------------------------------------------

Permit (halosulfuron) + additive

        Rate: 2/3 to 1.33 oz (0.032 to 0.064)
       Weeds: Redroot pigweed, common cocklebur, Venice mallow,
              common and giant ragweed, and sunflower.
       Apply: POST: Corn up to 36 inches tall. Drop nozzles must be
              used from 24 to 36 inches tall.
     Remarks: Good crop safety. Use NIS or oil additive with the
              addition of 28% UAN at 2 to 4 qt/A. Liquid fertilizer
              increases control pigweed and other species. Common
              lambsquarters is not controlled. Can be tank-mixed
              with Atrazine, Banvel, Clarity, Marksman, 2,4-D,
              Buctril, and Accent for greater weed control.
----------------------------------------------------------------------

Scorpion III (flumetsulam + clopyralid + 2,4-D acid)

        Rate: 1/4 lb (0.023 + 0.063 + 0.125)
       Weeds: Most broadleaf weeds including nightshade, cocklebur,
              sunflower, ragweed, and suppression of Canada thistle.
       Apply: POST: Corn up to 8 inches tall.
              Weeds: 2 to 4 leaf stage.
     Remarks: Apply with NIS at 0.25% v/v or NIS + 28% UAN at
              2.5% v/v. Addition of 28% UAN may improve control of
              weeds under dry conditions. Do not apply liquid
              fertilizer solutions as total carrier. Do not apply to
              corn previously applied with any Broadstrike product.
              Delay harvest until 85 days after application. Do not
              apply by air. There are no insecticide restrictions.
              Refer to label for crop rotation restrictions.
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Stinger (clopyralid)

        Rate: 1/3 to 2/3 pt (0.12 to 0.25)
       Weeds: Canada thistle and other broadleaf weeds.
       Apply: POST: Corn up to 24 inches tall. Thistle from 4 inches
              in diameter but before bud stage.
 Other weeds: Before 5-leaf stage.
     Remarks: Apply only to field corn. Majority of thistle shoots
              should be emerged at time of application. Wait 14 to
              20 days after application before cultivating. Restrict
              livestock grazing or harvest treated corn within 40
              days after last application. See narrative for
              rotational restrictions.
----------------------------------------------------------------------

Basis (rimsulfuron + thifensulfuron) + additive

        Rate: 1/3 oz (0.015)
       Weeds: Barnyardgrass, foxtails, redroot pigweed, wild
              mustard, common lambsquarters, annual smartweed, and
              other grass and broadleaf weeds.
       Apply: POST: Corn spike to 4-leaf (2 collar) stage. 
                                     Weeds 1 to 2 inches tall.
     Remarks: Apply with NIS or oil additive. Always add 28% UAN.
              Addition of 28% nitrogen enhances weed control. Do not
              apply to corn previously treated with Counter
              insecticide. See narrative rotational restrictions and
              registered tank-mix options.
----------------------------------------------------------------------

Basis Gold (nicosulfuron + rimsulfuron + atrazine)

        Rate: 14 oz (0.188 oz + 0.188 oz + 0.76)
       Weeds: Most all annual grass and broadleaf weeds including
              quackgrass.
       Apply: POST: Corn up to 12 inches tall.
     Remarks: Apply with oil adjuvant at 1 to 2% v/v. Use on corn
              hybrids of 88 or more days maturity. May be tank-mixed
              only with Banvel, Clarity, Hoernet, or Tough. Basis
              Gold at 14 oz/A contains 0.76 lb ai/A atrazine.
              Follow label for crop rotation restrictions.
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Accent (nicosulfuron) + additive

        Rate: 2/3 oz (0.0313)
       Weeds: Emerged grasses including wild-proso millet and
              quackgrass plus pigweed and smartweed.
       Apply: POST: Corn up to 36 inches.
     Remarks: Drop nozzles must be used from 24 to 36 inches tall.
              Apply with oil additive and 28% UAN. Do not apply to
              corn previously treated with Counter 15G insecticide.
              See narrative rotational restrictions and registered
              tank-mix options. Addition of 28% nitrogen enhances
              weed control.
----------------------------------------------------------------------

Accent (nicosulfuron) + atrazine

        Rate: 2/3 oz + 0.42 to 1.7 lb 90DF (0.5 oz + 0.375 to 1.5)
       Weeds: PRE and POST control of most grass and small-seeded
              broadleaf weeds.
       Apply: POST: Corn up to 12 inches tall. Weeds actively growing.
     Remarks: Add an oil adjuvant. MVO adjuvants enhances weed
              control. Addition of 28% UAN is recommended. Do not
              apply to corn taller than 12 inches tall.
----------------------------------------------------------------------

Accent (nicosulfuron) + Banvel, Clarity (dicamba)

        Rate: 2/3 oz + 0.5 to 1.5 pt 4S (0.5 oz + 0.25 to 0.5)
       Weeds: POST control of most grass and broadleaf weeds and
              suppression of Canada thistle.
       Apply: POST: Corn up to 8 inches tall. Apply with drop
              nozzles from 8 to 24 inches tall.
     Remarks: NIS is required. Do not apply the 1 pt/A rate of
              Banvel to corn greater than 8 inches tall. Addition
              of 28% UAN is recommended. Do not substitute oil
              additive for NIS.
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Sencor (metribuzin) + broadleaf herbicide

        Rate: 2 to 3 oz + rate for broadleaf herbicide
              (0.09 to 0.14) + rate for broadleaf herbicide)
       Weeds: Broadleaf weeds.
       Apply: POST Directed: Corn more than 8 inches tall.
     Remarks: Apply with 2,4-D, Banvel, or Buctril. Refer to label
              for adjuvant use, application information, range of
              crop stage at application, cultivation, potential for
              injury, and other restrictions.
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Gramoxone Extra (paraquat) RUP Directed Spray Only

        Rate: 13 to 24 fl oz (0.25 to 0.47)
       Weeds: Broadleaf and grass weeds.
       Apply: POST Directed: Corn more than 8 inches tall.
     Remarks: Treat no more than lower 3 inches of corn stalk. Apply
              with NIS at 0.25% v/v. May be tank-mixed with atrazine.
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A-1130, May 1997