Crop Production Management - Corn

Key management practices for organic corn production:

•Choose organically grown (when possible), non-GMO hybrids with high vigor,
high standability rates, disease and pest resistances, stress tolerance, high yield,
and a maturity date of 112 days or less.

•Plant on time, at the proper depth, in a well prepared seedbed, on narrow rows.

•Rotate crops.

•Achieve proper soil pH and good fertility.

•Choose the correct plant population.

Hybrid Selection

For organic growers seeking to identify appropriate corn hybrids, yield is not the
primary consideration. Producers should consider these key hybrid characteristics
for organic corn production:

•rapid early growth and vigor

•standability
•pest and disease resistance
•stress tolerance
•yield
Rapid early growth and vigor

Rapid early growth is essential to minimize the effects of seedling diseases and
insects, increase root volume, and reduce weed infestation. Hybrid seed
companies list seed vigor ratings. Few companies, however, list ratings covering
early growth. In general, early growth is closely related to hybrid maturity. Early to
medium maturing hybrids (102- to 114-day relative maturity) tend to exhibit better
early growth than do late hybrids (> 115-day relative maturity). The best way to
select hybrids with rapid early growth for North Carolina is to contact Cooperative
Extension agents, seed company representatives, and other growers who have
had experience with different corn hybrids.
Standability

Standability is important because it is a measure of how well the crop will stand
under difficult environmental conditions. Because pests and diseases can be
problems, it is important that an organic hybrid has the ability to avoid lodging
under stress. Most hybrid seed suppliers provide ratings for standability or stalk
or root strength.
Pest and Disease Resistance

Resistance to common seedling, leaf, and stalk diseases is an important characteristic for hybrids in
organic production systems. There are even some hybrids that tolerate insect pests such as European
corn borer and southern cornstalk borer. Unfortunately, most hybrids do not have resistance to a wide
range of diseases or pests. Growers should select hybrids that combine good early growth characteristics
with a good resistance package to diseases that are major problems in their area. In North Carolina the
major diseases of corn are grey leaf spot and northern and southern leaf blights.

Yield

Unfortunately, variety testing of corn under organic conditions is sparse. Past NC trials can be found at
the Organic Grains portal. Given the rapid turnover of hybrids, test results can rapidly fall out of date.
Growers should conduct their own hybrid comparisons by selecting four to six promising hybrids and
evaluating them on their farms with their management practices. The best procedure for grower testing of
hybrids is the strip test where each hybrid tested is grown adjacent to a common “tester” hybrid. The strip
test, with tester hybrids, permits any yield data collected to be adjusted for soil variability. If not using a
tester, growers should place the hybrids they are considering beside the hybrid that has performed best
for them in the past. Growers conducting their own hybrid evaluations must remember to select uniform
test fields with minimal soil variability and restrict comparisons to hybrids of the same maturity.
Planting Date

Planting date is crucial to the success of an organic production system. Planting

too early results in slow growth and increases weed competition, the incidence of
seedling diseases, and the likelihood of damage from seedling insects. On the
other hand, planting too late results in a greater risk of drought stress, increased
insect damage from second and third generations of European corn borers, and
reduced yield due to decreasing hours of daylight. The recommendations here
attempt to balance these considerations. In the NC tidewater and coastal plain,
plant organic corn between April 15 and May 15. In the NC piedmont, plant organic
corn between April 20 and May 20. In all NC locations, plant following at least two
days when average temperatures are above 65ºF. Depending on the soil type,
time soil preparation and planting date so that soils are moderately dry at planting
to minimize the risk of seedling diseases.
Seedbed Preparation and Planting Depth

Seedbed preparation should begin with a major tillage operation performed at

least a month before planting. If cover crops are used, they may need to be killed
and/or incorporated into soils earlier than one month before planting to allow for
residue decomposition and to avoid seed corn maggots. Heavy applications of
compost or manure should also be incorporated earlier. Follow up with at least
two light tillage operations to create a smooth, weed-free seedbed. The final
tillage operation should be performed on the day of planting to ensure that all
germinated weeds have been destroyed when the seed is placed in the ground.
Seeding depth is very important in an organic production system. Seeds planted
too deeply will be slow to emerge, and seedlings will have immediate weed
competition and a greater likelihood of damage caused by seedling diseases. A
seeding depth of just 1 inch is sufficient on most soils and allows for rapid
emergences.
Plant Population

Plant population is another important factor in organic corn production, especially when corn is grown on
sandy soils. Plant populations should be related to the moisture-holding capacities of each individual field. In
organic systems, corn plant populations per acre should be 10 percent higher than in conventional systems.
The higher plant population will increase light interception and reduce weed competition and the effects of
pest damage. On soils with good-to-excellent water-holding capacity, the goal is a stand of 30,000 to 33,000
plants per acre; on soils with average water-holding capacity, 25,000 to 28,000 plants per acre; and on soils
with poor waterholding capacity, no more than 22,000 plants per acre.

Row Spacing

Narrow rows permit more uniform plant distribution and result in rapid closing of the canopy. In choosing a
row width, balance the potential advantages that come from narrower rows against the additional machinery
cost and management that a narrow row system demands. Because cultivation is the primary weed control
measure in organic production, make rows wide enough to permit the use of a tractormounted cultivator. Row
spaces as narrow as 20 inches have been successful under organic conditions with alterations in cultivators
and guided steering systems
Soil Fertility

Corn generally requires from 120 to 160 lb of nitrogen per acre, 30 to 50 lb of phosphorus per acre, 80 to 100 lb
of potassium per acre, and smaller amounts of sulfur and micronutrients to obtain optimum yield. Organic corn
growers should design their systems so that the amount of nutrients added to the system offsets the amount
removed in the grain or forage. The local offices of the USDA Natural Resources Conservation Service,
Cooperative Extension, or the Soil and Water Conservation District can provide guidelines for a nutrient
management plan.

Weed Management
Grassy weeds and warm-season broadleaf weeds, such as cocklebur and morning-glory, will be among the most
difficult to control. Although tillage prior to planting can help reduce early-season weeds, many of the summer
annuals will continue to germinate and grow. It is very important to start with a clean seedbed and to till the soil just
before planting so the crop begins with a head start on new weed seedlings. This will make it much easier to use
cultivation to control grass and broadleaf weeds that are smaller than the corn. It is also important to take
advantage of the corn canopy’s ability to shade the soil. Shade reduces the number of weeds germinating and
slows their growth. Use of increased plant populations, narrower rows, row directions perpendicular to the path of
the sun, and tall-growing hybrids all increase canopy density and lead to quick canopy closure. Remember that
weed competition during the first four to six weeks after planting will cause the most damage in terms of yield
reductions. Weeds that emerge after canopy closure will have little effect on yield, although they can make harvest
more difficult. Chapter 7 has more information on managing weeds in organic production.
Insect Pest Management

Cultural practices are very important for establishing a vigorous, full corn stand. Stand establishment can
greatly influence pest populations as well as crop competitiveness and tolerance to pest feeding. In fields
where pests are historically abundant, do not plant organic corn if suitable, effective, and economical pest
management options are not available.

Crop rotation

Crop rotation is one of the most powerful tools for insect management and is also often the lowest-cost method
of control. Rotations of at least two years and use of a nongrass crop will reduce the levels of many pests
through starvation, interference with insect reproduction, or both. Rotation also gives the option of isolating corn
crops from one year to the next. This may or may not be effective for wireworm. Depending on the species, a
single generation of wireworm can take one to five years to complete. As a result, a multiyear rotation out of
corn may be needed to avoid this pest. Rotation in large units with a minimum of 800 to 1,000 feet between
current and previous corn is the most effective way to manage
moderately mobile pests such as billbugs.
Cover crops

Cover crops may reduce the abundance of some pests, although little research has been done in corn.
Alternatively, the density of certain pests, such as cutworms and probably wireworms, can be increased by
cover crop use.

Tillage

Insect pests that feed on seed and small seedlings are typically found in the soil or at the soil surface.
Populations of wireworms, cutworms, grubs, seed corn beetles, and other pests can be reduced with winter
or early spring disking and the accompanying bird feeding and exposure. The combined action of these
factors can give meaningful protection to planted seed and small seedlings. No-till organic corn using cover
crop mulches is being tested around the state, but this system is not as well understood as no-till soybeans.

Rapid germination and seedling grow-off

Rapid germination and seedling grow-off reduces the time corn seed and seedlings spend in the most
vulnerable stage between germination and the six-leaf stage and helps the crop gain a size advantage over
weeds. Losses to seedling insects and other pests can be reduced by promoting early germination through
row-bedding, seeding at the recommended depth, hybrid selection for performance under cool conditions,
and adequate soil fertility.
Crop maturity
In corn, timely maturity of the crop almost always reduces insect damage. Certain
pest insects and pathogens (for example, late-season corn borers and fall army
worms) reach high densities in late July and August and may severely infest late-
maturing corn. Timely planting and avoidance of late-maturing hybrids (over 120
days) will reduce the level of pests attracted to the crop in late season and prevent
yield loss. When planted early, hybrids that mature in 112 days or less will usually
avoid late-season caterpillar attack.

Hybrid selection

Rapid germination, early vigor, strong ear shanks, tight husks, resistance to stalk
rots and other pests, strong stalks, and uniform performance over a wide
population range are factors influenced by genetics that may reduce losses to
insects.
Major Corn Insect Pests and Management

Corn billbugs

Bill bugs can be serious pests of corn seedlings. No insecticide approved for organic use has activity against
billbugs. Combining cultural tactics—rotation and isolation from previous corn crops—along with rapid
seedling emergence and grow-off should help prevent concentrations of adult billbugs and promote rapid
accumulation of tolerance. Three additional billbug management tactics are (1) avoiding areas with abundant
nutsedge, which is an alternative host for billbug; (2) avoiding no-till production for organic corn because no-till
soils warm more slowly and delay germination and grow-off; and (3) planting at the earliest possible date to
allow seedling growth prior to billbug adult emergence.

Wireworm and black cutworm

In organic systems, the major tactics for reducing populations of these insects will be disk cultivation and
avoidance of no-till situations. Cultural methods that promote rapid seedling growth and seeding at adequately
high populations to allow some seedling loss can also be important.
European corn borer (ECB) and southern corn-stalk borer

Borers likely occur at some level in all North Carolina cornfields. Their populations fluctuate greatly between
years and sometimes within a single growing season. The organic farmer can influence the abundance of
these borers through rotation, site selection (away from first-generation ECB nursery areas in potato and
wheat fields), early planting, and use of short-season corn hybrids. Taking these actions to manage both
space and time will help avoid high populations and promote tolerance for those borers that are present.
Organically approved spinosad insecticides are labeled for ECB on corn, but they are expensive and are not
likely to be effective when sprayed on tall corn. For ECB scouting procedures and thresholds, consult your
county Extension center or the Extension corn portal.

Western corn rootworm

Western corn rootworm is a pest only in nonrotated corn. It can be successfully managed in an organic
system by rotating corn with other crops.
Key Diseases and Management

Six key diseases—Grey leaf spot, Northern and Southern corn blights, seed rots and seedling blights, stalk
rots, and charcoal rot, which are usually controlled in conventional systems either by fungicides or management
practices—can have significant impacts on organically grown corn. Growers should be aware of these diseases
and select hybrids and management practices that reduce the risk they pose. Grey leaf spot and Northern and
Southern corn blights are best managed in organic systems by choosing resistant hybrids. While there are
many other diseases that can attack corn, they rarely cause economic loss. Pictures of these field corn
diseases can be found in Common and Southern Rusts.

Seed rots and seedling blights

Seed rots and seedling blights caused by species of Fusarium, Stenocarpella, Pythium, and other fungiare
often associated with the term “damping-off.” Plants die at emergence or within a few days of emergence.
These diseases are more prevalent in poorly drained, excessively compacted, or cold, wet soils. Planting old or
poor quality seed with mechanical injury will increase seed rot and seedling blight, as will planting seed too
deep in wet, heavy soils. Seed vigor
ratings are often used to select hybrids with genetic resistance to seed rots and seedling blight.
Stalk rots

Stalk rots (caused principally by the fungi Stenocarpella zeae and species of Fusarium as well
as Colletotrichum graminicola) are present each year and may cause considerable damage, particularly if
abundant rainfall occurs during the latter part of the growing season. Stalks previously injured by cold, leaf
diseases, or insects are especially susceptible to attack by these fungi. Diseased stalks ripen prematurely
and are subject to excessive stalk breaking. Stalk rots not only add to the cost of harvesting but also bring the
ears in contact with the ground, increasing their chance of rotting. Adequate fertility (particularly adequate
potassium) is the key to controlling stalk rot.

Charcoal rot

Charcoal rot (caused by the fungus Macrophominaphaseolina) becomes most evident with the onset of hot
dry weather. It may cause stalk rot, stunting, and death of the corn plant. This disease is often considered to
be stress-related. Typically, when this disease occurs in North Carolina, soil fertility and pH are at very low
levels. Although the fungus survives in the soil, rotation is not generally helpful because most crops are
susceptible to this disease. Supplying
adequate nutrition and water is the principal means of control. Hybrid resistance in corn has not been
documented.
Harvesting

Early harvesting usually avoids crop damage from pests or hurricanes and
prevents field losses resulting from ear drop and fungal pathogens. Probably the
most important reason for timely harvest is the potential for yield reductions
resulting from ear loss and ear rots due to stalk lodging, ear drops, and reductions
in kernel weight. Fungal diseases that infect the corn kernel also cause more
problems as harvest is delayed. Mycotoxins, such as aflatoxin and fumonisin,
which are produced by fungal pathogens, also increase as harvest is delayed and
may result in corn that is unsuitable for human or livestock consumption. Ideally,
corn harvest should begin as soon as the grain reaches moisture levels of 25
percent or less. Under favorable conditions, corn should be ready to harvest in 10
days or less following the black layer formation at the base of the kernels.