Corn:Guidelines
GUIDELINES: CORN PRODUCTION
Contents
- 1 STATISTICS
- 2 OUTLINE OF MANAGEMENT ACTIVITIES
- 3 CORN DEVELOPMENT
- 3.1 Stages of Development
- 3.2 =V6 Stage
- 3.2.1 V9 Stage
- 3.2.2 V12 Stage
- 3.2.3 Vl5 Stage
- 3.2.4 V18 Stage
- 3.2.5 VT Stage
- 3.2.6 RI Stage--Silking
- 3.2.7 R2 Stage---Blister (10-14 days after silking)
- 3.2.8 R3 Stage--Milk (18-22 days after silking)
- 3.2.9 R4 Stage---Dough (24-28 days after silking)
- 3.2.10 R5 Stage---Dent (35-42 days after silking)
- 3.2.11 R6 Stage---Physiological Maturity (55-65 days after silking)
- 3.2.12 Conclusions
- 4 GROWTH REQUIREMENTS
- 5 CULTURAL PRACTICES
- 6 FERTILIZER APPLICATION
- 7 VARIETIES
- 8 Misc. Photos
STATISTICS
OUTLINE OF MANAGEMENT ACTIVITIES
Cultural Practices
_____ Turn under or harrow all corn stubble after the previous season. _____ Test soil for nutrient status and pH every year. Maintain records of test results and fertilizer applications. _____ Test soil organic matter at least once every three years. _____ Apply fertilizer and lime according to test results, crop requirements, and expected uptake, accounting for additional nitrogen from organic matter, compost, manure, and cover crops. _____ Apply nitrogen fertilizer by split application (Some applied at planting and some as a sidedress, as needed). _____ Note: A typical corn crop removes approximately 10 lbs./acre of nitrogen between germination and six-leaf stage. Pre-plant broadcast of N should generally be avoided. _____ If fertilizer is applied at planting, it should be applied in a band to increase efficiency and to reduce total fertilizer required. _____ Note: More than a total of 80 lb./acre of N plus K<->2</->O applied in a band may cause crop burning. _____ Take a pre-sidedress nitrate test and apply nitrogen sidedress according to test results. _____ Use a winter cover crop to preceded the corn crop. In, particular use a legume or legume/grass mix cover crop. _____ Calculate the cover crop's nitrogen contribution and adjust fertilizer application appropriately. _____ Adjust fertilizer application for compost or manure applications. _____ Use an experimental plot to test reduced rates of fertilizer or organic sources of nutrient (e.g. composts, cover crops).
Pesticide Management
_____ Use approved and registered pesticides according to label. _____ Maintain application records including date, location, applicator, target pest, pesticide name, EPA registration number, formulation, rate and number of acres treated. _____ Calibrate all sprayers at the start of the season. _____ Minimize pesticide drift. _____ Develop and implement a resistance management plan. _____ Select pesticides which will preserve natural enemies of pests. _____ Use separate sprayers for herbicides and insecticides. _____ Check sprayer(s) calibration at least once during the season and recalibrate as needed _____ Maintain records of planting dates for treated fields. _____ Keep records of stage of crop of treated field. _____ Use water-sensitive spray cards to test coverage of leaf surfaces. _____ Use a boom sprayer with double-drop nozzles for sprays where coverage of the ear zone is desirable, or if a mist blower is used, blocks are not greater than 12 rows wide.
Insect Pest Management
_____ Scout "SUSPECT INSECTS" Aphids Armyworms Corn Earworm Corn Stunt Leafhopper Cucumber Beetles Cutworms Flea Beetles Grasshoppers Seedcorn Maggot Spider Mites Thrips Wireworms
_____ Use a pheromone trap for Corn Earworm, European Corn Borer and Fall Armyworm, where present. _____ Insecticide applications for Corn Earworm, ECB, and Fall Armyworm where present, should correspond to action thresholds recommended by Cooperative Extension. _____ Scout for occasional pests for which action thresholds are not available. _____ Use floating row covers in seedling through whorl stage to reduce European Corn Borer, where present. _____ Use biological insecticides (e.g. Bts) or beneficial insects in at least part of the acreage to keep insect pests below economic injury levels.
Disease Pest Management
_____ Use disease resistant cultivars where there is a history of maize dwarf mosaic virus. _____ Submit all plants with maize dwarf mosaic virus symptoms to a diagnostic lab for confirmation. _____ Use tolerant cultivars where there is a field history of Stewart's wilt disease.
Weed Pest Management
_____ Scout "SUSPECT WEEDS" barley, hare (Hordeum murinum ssp. leporinum) barnyardgrass (Echinochloa crus-galli) bermudagrass (Cynodon dactylon) bindweed, field (Convolvulus arvensis) cocklebur, common (Xanthium strumarium) datura, sacred (Datura wrightii) goosefoot (Chenopodium spp.) groundcherries (Physalis spp.) johnsongrass (Sorghum halepense) junglerice (Echinochloa colona) knapweed, Russian (Acroptilon repens) knotweed, common (Polygonum arenastrum) lambsquarters, common (Chenopodium album) lettuce, prickly (Lactuca serriola) morningglories (Ipomoea spp.) nightshade, black (Solanum nigrum) nightshade, hairy (Solanum sarrachoides) nightshade, silverleaf (Solanum elaeagnifolium) nutsedge, purple (Cyperus rotundus) nutsedge, yellow (Cyperus esculentus) oat, wild (Avena fatua) pigweed, redroot (Amaranthus retroflexus) puncturevine (Tribulus terrestris) purslane, common (Portulaca oleracea) purslane, horse (Trianthema portulacastrum) shattercane (Sorghum bicolor) sprangletops (Leptochloa spp.) spurge, spotted (Chamaesyce maculata) sunflower, common (Helianthus annuus) thistle, Russian (Salsola tragus) velvetleaf (Abutilon theophrasti) wheats (Triticum spp.)
_____ Prepare weed maps in mid-to-late season, indicating significant weed species and their location.
_____ Base all herbicide rate, selection and spot or strip sprays on weed survey results.
_____ Weeds may be controlled by cultivation, with no herbicide applied.
_____ Use reduced rates of herbicide through banding of herbicides and cultivation.
_____ Use reduced rates of herbicide through delayed application of reduced rates of herbicide.
_____ Prevent weeds within the field, alleys and roadways from going to seed.
_____ Use an experimental plot to test different weed management techniques.
Weather and Crop Monitoring
_____ Monitor weather and crop parameters _____ Keep daily records. Date: Min/max temperatures: Rainfall: Hours of leaf wetness: Stage of tree development (by cultivar, weekly):
CORN DEVELOPMENT
All corn varieties rely upon water and nutrients from the soil and carbon dioxide from the air to grow and develop. In addition, they all follow the same general pattern of development but the specific time between growth stages, planting dates, and planting locations will vary among species.
Stages of Development
The stages of development are broken down into vegetative and reproductive stages and then each of these are broken down into subdivisions. There are generally 12-18 subdivisions in the vegetative stages and approximately six reproductive subdivisions.
(Reference: How a Corn Plant Develops, Special Report No. 48, Iowa State University)
Vegetative Stages and Development
Germination and emergence occur in the first vegetative stage when the seed absorbs water and begins to grow. The radicle pushes into the soil to anchor the plant and the coleoptile pushes through the soil surface. All roots tend to grow at an angle of 25-30° from horizontal, regardless of how deep the seeds were planted. If conditions are warm and moist, emergence should occur within 4-5 days after planting. By choosing hybrids adaptable to the area and planting in proper conditions, losses will be minimized during the growing season. Fertilizer is extremely important in this stage, even though the uptake is in relatively small amounts.
V3 Stage
By the third vegetative stage, root hairs have begun to grow from the nodal roots and all leaves and ear shoots are being formed. The plant is about eight inches tall but the tasseling point still has not emerged. Leaves that have emerged are laid side to side as they appear on the stalk. At this time, cold soil temperature, flooding, hail, or excessive weed competition can damage the exposed leaves.
=V6 Stage
When plants reach the sixth vegetative stage, the tassels are above the soil surface and the stalk is elongating quickly. Some ear shoots or tillers are visible and form from just above the leaf that grew from the same node. Fertilizer placement is not so critical at this time and any deficiencies observed can be remedied through broadcast fertilization.
V9 Stage
At the ninth vegetative stage, many ear shoots are visible and grow from every above ground node except those right below the tassel. Each ear shoot develops faster than the ear above it on the stalk but this growth will gradually slow and only the upper one or two ears will be able to be harvested. The stalk continues to elongate and the tassel begins to develop rapidly. During this stage, nutrient and dry weight accumulation begins and will continue into the reproductive stages. Because the plant is growing so rapidly, soil nutrients and water supplies are in high demand.
V12 Stage
The number of potential kernels on each ear and the size of the ear are being determined in the twelfth vegetative stage. Moisture and nutrient levels are extremely important at this time to determine the number of potential seeds and size of ears harvested.
Vl5 Stage
Plants in the fifteenth vegetative stage are only a few days away from the first reproductive stage and this is a critical period in the development of seed determination. Silks are just beginning to grow from the upper ears at this time. Water stress before silking is the greatest factor affecting larger seed yield and should be avoided. This is the most important time for effective irrigation.
V18 Stage
In the final vegetative stage, the upper ear shoots and ear development are initiated. The silks from the basal ear ovules are first to elongate and the silks from the ear tips are last to elongate. Brace roots are forming to support the plant and are important in the uptake of water and nutrients. Stress at this time delays ear and seed development and may delay silking if it is severe.
Field corn, pre-tassel (H. F. Schwartz; Colorado State University)
VT Stage
The tasseling stage begins when the last branch of the tassel is completely visible. At this time, the plant reaches its full height, silks emerge, and pollen begins to shed. The plants are vulnerable to hail damage in this stage because the tassels and leaves are all exposed. The pollen will shed for 1-2 weeks, which will allow all the silks to emerge and be exposed to pollen for fertilization.
Field corn in tassel (H. F. Schwartz; Colorado State University)
Field corn in tassel (H. F. Schwartz; Colorado State University)
RI Stage--Silking
The first reproductive stage is when the pollen becomes caught on the silks and fertilizes the ovule. It takes 2-3 days for the entire ear to become pollinated and the silks will grow 1-1 1/2 inches a day until it is fertilized. The number of kernels is being determined at this time, which can be effected by environmental stresses causing poor pollination and seed set.
Field corn ear, late silk stage (H. F. Schwartz; Colorado State University)
Field corn ear, late silk stage (H. F. Schwartz; Colorado State University)
R2 Stage---Blister (10-14 days after silking)
In the second reproductive stage, the kernels are white on the outside and developing the plant parts inside forming a tiny corn plant. The kernels have also grown out from the surrounding cob. Starch is accumulating in the seeds, beginning rapid dry matter accumulation.
R3 Stage--Milk (18-22 days after silking)
In the third reproductive stage, the kernels develop a yellow color and the inner fluid is a milky white starch. Most of the kernels have grown out from the surrounding cob and the silks are drying out and turning brown. The kernels are rapidly accumulating dry matter and are about 80% moisture and filling with starch. The final yield will depend on the number and weight of the developing kernels and stress at this time can still reduce yields.
Field corn, early milk stage (H. F. Schwartz; Colorado State University)
Field corn, milk stage (H. F. Schwartz; Colorado State University)
Field corn, milk stage (H. F. Schwartz; Colorado State University)
Field corn, milk stage (H. F. Schwartz; Colorado State University)
R4 Stage---Dough (24-28 days after silking)
During the fourth reproductive stage the starch continues to accumulate and the milky inner fluid of the kernel begins to thicken. The cob begins turning a light red to pink color because of the changes in the lemmas and paleas. The kernels are only at about 70% moisture, which causes the consistency within the kernel to be doughy.
R5 Stage---Dent (35-42 days after silking)
At this stage, nearly all the kernels are dented or are denting and the cob becomes dark red in color. The kernels are also drying now because a small hard white layer of starch is forming. This starch layer will eventually move toward the base of the kernel. It is important that the plant not be stressed during this phase because it could reduce kernel weight. Also, environmental conditions such as frost may halt dry matter accumulation and cause delays in harvest operations because frost-damaged corn dries slowly. At this stage, the kernels have about 55% moisture content.
Field corn ear - dent (H. F. Schwartz; Colorado State University)
Field corn ear - dent (H. F. Schwartz; Colorado State University)
Field corn ear - dent (H. F. Schwartz; Colorado State University)
Field corn ear - dent (H. F. Schwartz; Colorado State University)
Field corn ears - dent (H. F. Schwartz; Colorado State University)
R6 Stage---Physiological Maturity (55-65 days after silking)
The final reproductive stage occurs when all the kernels on the ear have attained their maximum dry weight or maximum dry matter accumulation. The starch layer has moved to the cob now and a black or brown abscission layer is formed. The husks and many leaves may have turned brown and dried out. The kernels are at about 30-35% moisture, but this is still too moist for proper storage, which requires 13-15% moisture. It is advised not to harvest the corn in this stage, but to wait for a few days until the moisture levels have fallen. However, the correct timing for harvest depends greatly on the variety planted.
Conclusions
The dry weight is corn accumulated throughout the season with the bulk accumulating late in the season when the plants' many leaves are exposed to sunlight. Highest yields will be obtained only where environmental conditions are favorable at all stages of growth.
GROWTH REQUIREMENTS
Although nutrient uptake is slow in the early growing stages, the nutrient concentrations in the soil surrounding the roots of the small plant at that stage often must be high. The potassium uptake is usually complete at the time of silking, but nitrogen and phosphorus will continue to be used until maturity. Nutrient shortages result in small leaves and ears.
Nutrient Uptake
Dry matter accumulates as the leaf area increases. Leaf growth is usually complete about 50-60 days after emergence. Stem growth begins about 3 weeks after emergence and begins rather slowly. Stalk growth occurs before tasseling and cob growth occurs during and after pollination. The corn grains begin forming shortly after silking and at this time the photosynthetic products go from the leaves to the grain.
Nitrogen
Corn requires a great amount of nitrogen, which is mostly used around silking and tasseling.
Corn leaf testing for nitrate levels (Reagon Waskom ?; Colorado State University)
Corn leaf testing for nitrate levels (Reagon Waskom ?; Colorado State University)
Phosphorus
Phosphorus is important for the plants to reach maturity in a timely fashion and encourages pollination. When phosphorus is deficient, it is translocated from older to younger leaves. Soon after grain begins to form, phosphorus moves into the grain. Ears may not be completely pollinated due to phosphorus deficiency. Young plants are usually spindly and dark green, leaves are narrow, and leaves and stems may become purple.
Corn response to phosphorus (; Colorado State University)
Potassium
Potassium is important earlier in the season and can easily move from old to young leaves. Plants that are deficient are dry and brittle along the edges, ears do not completely fill, and kernels are loose and chaffy.
Temperature=
High temperatures are important in high corn yields. Early spring temperatures allow earlier planting, faster emergence, and early growth. Temperature also effects the rate in which plants produce and burn sugar.
Water
Corn needs about 18 inches of water during the growing season with the most critical time during silking and pollination. It is important that plants have enough water at this time to avoid limiting the number of kernels that will develop. Corn roots can grow to a depth of five feet, which need to remain moist.
CULTURAL PRACTICES
Achieving top corn yields requires top-yielding hybrids, high plant populations, early planting dates and high fertility levels. Elimination of competition from weeds, insects, and diseases is also important for good yields. However, most fields do not reach their yield potential because environmental factors such as soil, moisture availability, light and temperature limit the field from reaching its potential.
Plant Population
Plant population is based on the number of plants per field, which may vary according to the variety planted. The overall corn yield is determined by the number and weight of the ears harvested per acre.
Plant Date
Corn planted earlier in the season will produce higher yields because they will be able to maximize the growing season. These plants will be shorter and the ears will mature earlier.
FERTILIZER APPLICATION
Early fertilization is important for developing plant parts that are preparing to grow. When the plants are small, the nutrient uptake is in relatively low concentrations. Having a large nutrient supply available will determine the final size of the leaves, ears, and other plant parts, which ultimately affect yields. The roots should be moist to take in the necessary nutrients, but they should not be waterlogged. Fertilizer can be applied either in a band to the side and slightly below the seed when planting, broadcast or through irrigation. Because the roots can be close to the surface, it is important when cultivating or side-dressing fertilizers not to harm the root system. Fertilizer requirements will change based on soil type, temperature, and variety planted. In most cases, nitrogen will be the nutrient most in demand followed by phosphorus and potassium. A soil analysis test should be taken to apply the proper amount of all nutrients and avoid any nutrient deficiencies.
SUMMARY
Farmers can control many factors that will encourage high yields such as proper hybrid selection, adequate nutrient availability, planting date and proper irrigation.
The Economics of Corn Fertilization
Many factors affect how much fertilizer should be applied but the question should be given serious consideration. Farms can lose money by applying too much fertilizer or minimize losses by applying too little fertilizer.
EFFECT OF CORN PRICE
Adequate fertilizer programs are the best way to achieve high yielding corn crops.
MINIMIZE PRODUCTION COSTS PER BUSHEL OF CORN
Minimizing production costs per bushel requires that maximum yields be attained. This can be done by selecting the proper hybrid, using a high plant population, planting early, controlling weeds, diseases, and insects, and maintaining a high level of soil fertility through proper fertilizer application.
VARIETIES
Blue corn seeds (H. F. Schwartz; Colorado State University)
Broom corn seeds (H. F. Schwartz; Colorado State University)
Dent corn seeds (H. F. Schwartz; Colorado State University)
Flint corn seeds (H. F. Schwartz; Colorado State University)
Red popcorn seeds (H. F. Schwartz; Colorado State University)
White (flour) corn seeds (H. F. Schwartz; Colorado State University)
White popcorn seeds (H. F. Schwartz; Colorado State University)
White sweet corn seeds (H. F. Schwartz; Colorado State University)
Yellow popcorn seeds (H. F. Schwartz; Colorado State University)
Yellow sweet corn seeds (H. F. Schwartz; Colorado State University)
Yellow sweet corn seeds (H. F. Schwartz; Colorado State University)
Misc. Photos
Corn planted in wheat stubble (; Colorado State University)
Ear, 4 w/tw scale on grain (; Colorado State University)
Ear - half pollinated (; Colorado State University)
Field - good - green (; Colorado State University)
Harvest gleaner combine (; Colorado State University)
Plane one good green ear (; Colorado State University)
Root washed/good (; Colorado State University)
Silage harvesting (; Colorado State University)
Silage harvesting (; Colorado State University)
Silage pit/crawler tractor (; Colorado State University)
Stalks - corn snap (; Colorado State University)
