A-834 July, 2004

Basics of Corn Production in North Dakota

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Corn Production in North Dakota

Corn is becoming an increasingly important crop in North Dakota, with the area planted for grain nearly doubling in the last three decades. Since 2002, more than 1 million acres are cultivated with corn each year. Grain yield of corn in the state has increased at a remarkable rate in the recent past, with yields now consistently averaging over 100 bushels per acre. The importance of corn silage in North Dakota has been on the decline, with the 180,000 acres planted in 2002 accounting for only about 60 percent of the area planted in the early 1970s.

Several factors have contributed to the increased interest by farmers in corn production for grain. First, the productivity of early maturing corn hybrids available to farmers has increased significantly. Gains in the genetic potential for yield of adapted hybrids have averaged 2 to 5 percent per year and there is no evidence that the genetic yield potential is approaching a plateau.

Second, the recent weather patterns have been more favorable for corn production relative to other cereal options. The current weather pattern of higher rainfall in the eastern third of the state, particularly in July and August during the period of high water use in corn, has been favorable to corn growth and at the same time been detrimental to small grain production, as these environmental conditions favor the development of fusarium head blight (scab), a pernicious disease of wheat and barley.

Environment and Corn Growth

Corn is currently grown in every county in the state, though the productivity and risk of production varies considerably from region to region. Temperature, rainfall and radiation are the major environmental factors that influence the growth and yield of corn.

Temperature and moisture are of particular concern in North Dakota. Temperature affects the rate of corn growth and the length of the growing season. Although corn is classified as a warm season crop, it still yields best when temperatures are moderate.

The potential productivity of corn is also directly related to the length of the growing season. The longer the growing season, the longer the corn plant has to photosynthesize and accumulate dry matter for grain yield.

Growing degree day (GDD) accumulations, also referred to as heat units, are the most common way of characterizing the length of the growing season. Unlike the number of days between killing frosts, GGD provides quantitative information about temperature during the growing season. In calculating GDD for corn, temperatures from a lower limit of 50 degrees and an upper limit of 86 degrees are accumulated for the growing season by applying the formula below to each day's maximum and minimum temperatures.

Maximum temperatures higher than 86 degrees are entered as 86 and temperatures below 50 degrees are entered as 50 in the formula. GDDs are accumulated from seedling emergence until physiological maturity. Historical as well as current season GGD accumulations can be obtained from the North Dakota State University NDAWN weather site at http://ndawn.ndsu.nodak.edu/application/corn degreedaysform.html.

Kernel moisture content at physiological maturity generally averages about 33 to 35 percent. 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 injured by frost after that point. Hybrids may vary up to 10 percent in kernel moisture at physiological maturity.

GDD accumulations vary considerably in the state, from up to 2,400 GDD in the southeast to less than 1,700 GDD in some seasons in the north. Matching the maturity length of a corn hybrid with the likely GDD accumulations at a given location is one of the basic management practices for successfully producing corn. Minimum soil temperatures of 46-50 degrees are required for corn germination and seedling growth.

Corn can tolerate some frost in the seedling stage and will recover from most early season frost damage because the growing point remains below or at the soil surface until the corn plant reaches the five-leaf stage (three to six weeks after planting, depending on soil and air temperature after planting). Beyond this stage, frost can kill corn.

Prolonged cold weather that reduces the soil temperatures two inches below the surface to below freezing can also kill corn seedlings regardless of their stage of development. Frost-kill in the fall after the kernels have reached maximum dry matter content hastens drying. However, freezing temperatures before physiological maturity (black layer) may slow dry-down, lower test weight and lower grain quality.

High ambient temperature or moisture stress can greatly affect corn silking and pollination. Pollen shed and silking often occur during the hottest period of the growing season. Total days of pollen production may be shortened, but the main effect of moisture stress is a delay in silk emergence.

Silk emergence and elongation are highly dependent on moisture. When soil moisture is in short supply, silks will grow little, if at all, during the day when water transpiration is high.

Under severe stress, some plants will not form any silks, or silks will emerge after pollen production has ceased, resulting in barren or poorly developed ears. High plant populations in moisture-limiting environments add to moisture stress and will increase silking problems with reduced kernel set.

The lack of moisture frequently limits the productivity of corn in North Dakota, particularly in non-irrigated areas in the western two-thirds of the state. Corn is one of the most efficient crops for dry matter production relative to water used. However, given its higher yield potential, corn is a relatively heavy water user. As a general rule, 16 inches of water are required to produce 100 bushels of corn grain compared to 13 inches required for 32 bushels of wheat.

Some of the basic recommendations for growing corn, such as crop rotation, plant population and tillage, vary in the state depending on the moisture that will be available to the crop. Certainly, careful management is needed in the drier parts of the state to reduce the risk of crop failure.

GDD=     (Maximum Temperature + Minimum Temperature)     -50
                                                  2

Hybrid Selection

Literally hundreds of corn hybrids are available commercially in the United States. Although only a fraction of those hybrids are actually marketed in North Dakota, the number of hybrids that are adapted to any one area of North Dakota is substantial. Furthermore, because of rapid genetic improvement that seed companies are currently able to achieve, many hybrids remain in the market for less than five years.

The process of selecting hybrids should be a continual process. Important criteria to consider when selecting a hybrid are yield, maturity, specialty traits and stalk quality. Test new hybrids in a small area on your farm before growing them on large areas. Growing more than one hybrid introduces genetic diversity and helps reduce the risks associated with growing a single genotype. The same hybrid may be marketed by several different companies, as the inbreds used to make these hybrids can be purchased from foundation seed companies without proprietary restriction.

If you intend to diversify the genetics on your farm, purchase all your hybrids from one company or purchase only those hybrids that are known to have distinct differences in the field in order to avoid buying the same hybrid from different companies.

Seed costs have increased markedly in the last decade and vary substantially depending on the company and the traits included in the hybrid. Most hybrids that are currently sold are single-cross hybrids. They generally offer the highest yield potential but are also the most costly to produce.

Three-way and double-cross hybrids are available on a limited scale, and because of their lower seed price, might be considered for drier regions of the state where yield expectation are low due to water limitations.

Seed costs should be determined on a per acre basis and the expected income differences (grain yield x price) compared with seed cost differences.

Planting cheap seed may not lead to a lower cost per bushel grown if the hybrid is not high-yielding or well-adapted to the region. Don't spend money on technology traits that are not needed. Generally a hybrid without the specialty trait with similar genetics and yield potential is available from the same company.

Grain yield

Grain yield is obviously one of the most important factors to consider in selecting a hybrid. Given the large number of hybrids on the market, finding data that compares hybrids of interest may be difficult. Most published yield trials have only a limited set of hybrids that are adapted to a given region.

Data from yield trials conducted by North Dakota State University and University of Minnesota breeders and agronomists at various test locations throughout the states are updated and reported annually. Information is also available at regional research and extension centers. These trials are comprised of a limited number of hybrids submitted by the companies that are commercially active in the state. The North Dakota data can be viewed at www.ag.ndsu.nodak.edu/aginfo/variety/corngrain.htm and the Minnesota data at www.maes.umn.edu/maespubs/vartrial/cropages/cornpage.html.

Commercial seed corn companies also conduct testing programs. Company field tests results are usually of greatest value in comparing available hybrids within a given company. Data from county and company strip tests, though not as rigorous for comparison purposes as replicated trials, can be a good way to see how a new hybrid will look in the field.

When comparing hybrids, it is important to look at harvest moisture in addition to grain yield. High grain yields with high moisture does not necessarily equate to high profits!

Maturity

Select hybrids which have a maturity length adapted to the GDD accumulations for your region of the state. Most seed companies define the maturity of their hybrids using the Relative Maturity (RM) rating system. The term "relative maturity" does not define how many days a hybrid needs to mature, but is used to designate the length of time required for a hybrid to reach maturity compared to standard hybrids which have been grown in an area for a long time.

A few companies also indicate the number of growing degree days required for the hybrid to reach maturity. The relationship between relative maturity and GDD is summarized in Table 1. Later-maturing hybrids almost always have higher grain yield potential than earlier-maturing ones. Hybrids that are too late for a given environment, however, will have excessive grain moisture at harvest or may not reach physiological maturity in some seasons.

 

Table 1. Approximate relative maturity of hybrids that are adapted to environments with the indicated GDD accumulations from planting until killing frost.
Accumulated GDD (Heat Units)	Relative Maturity (Days)
1750-1850	70
1851-1950	75
1951-2050	80
2051-2150	85
2151-2250	90
2251-2350	95
2351-2450	100
2451-2500	105

Balance between lateness for yield and earliness for low grain moisture is key to obtaining the most profit from a crop. Grain drying costs can quickly negate any gains achieved with grain yield increases that may be associated with later maturity. General guidelines for hybrid maturities adapted to the various regions of North Dakota are summarized in Figure 1.

When comparing hybrids in yield trials, look at both the relative grain yield and the relative moisture at the time of harvest.

One way to compare hybrids that differ in moisture content at harvest is to convert them to a dried grain value. This is done by multiplying the grain yield of the hybrid by the price of corn and then subtracting the cost of drying the hybrid to 15.5 percent moisture.

For example, to compare hybrid A with a grain yield of 130 bushels/acre and a moisture content of 19 percent with hybrid B with a grain yield of 136 bushel and moisture content of 25 percent, convert both to their dried grain value. In this example, if we use a corn price of $2.25/bushel and a drying cost of 3 cents per percent moisture per bushel above 15.5 percent, hybrid A and hybrid B would have dried grain values of $274.95 and $267.24, respectively [(130 b./acre X $2.25) - (130 bu./acre X 4.5% X 0.03) = $274.95 and (136 bu./acre X $2.25) - (136 bu./acre X 9.5% X 0.03) = $267.24]. In this example, hybrid A, which produced the most dried grain value, should be selected to the higher-yielding hybrid B.

Another method that requires less mathematical calculation is the performance index (PI). The performance index is calculated using the following formula:

P.I. = [(Grain yield of a specific hybrid/grain yield of the mean of all hybrids in the trial)/(Grain moisture of a specific hybrid/grain moisture of the mean of all hybrids in the trial)] x 100.

Hybrids with the highest yield and the largest PIs are considered the most suitable as far as yield and grain moisture at harvest are concerned. Those with a PI greater than 100 are considered better than average for the environment where they were tested.

If you have a large number of corn acres, to spread the risk and workload at harvest, plant hybrids of differing maturities.

A good rule is to plant 25 percent of your acres with early hybrids (five to seven days earlier than the recommended RM), 50 percent of your acres with adapted maturity hybrids and 25 percent of your acres to full season hybrids (five to seven days later than recommended) for your area. This will not only reduce the risk associated with an unusually short season, but will also diversify the genetics of your hybrids across the farm, thus limiting the potential for other losses arising from diseases or insect problems that may be hybrid specific or plant stage specific.

The strategy of growing hybrids with differing maturities may also help spread out the harvest season. Moreover, early harvested corn in some seasons may fetch better market prices.

Technology traits

A number of proprietary technology traits are currently available in corn that should be considered when selecting a hybrid. The presence of these traits in a hybrid does not directly affect yield but protects the plant from insects or imparts herbicide resistance. Many corn hybrids are currently available with single or multiple technology traits. Most of the technology traits require the payment of a technology fee, which is added to the seed price. Carefully consider the cost-benefit as well as market restrictions associated with some traits (i.e. the European Union restricts the import of Roundup Ready corn) before paying the extra cost for the technology. The fructose processing facility in southeastern North Dakota currently does not buy Roundup Ready hybrids. As with any new technology, you should carefully consider the advantages and disadvantages of using a hybrid with a technology trait in your own farming operation.

Traits currently available include the following:

Herculex I^® _ This is a transgenic trait that provides resistance to European corn borer, southwestern corn borer, fall armyworm, black cutworm and western bean cutworm, and moderate resistance to corn earworm. This transgenic trait is generally linked with another transgenic trait (Liberty^®) that imparts glufosinate herbicide tolerance. The Herculex I transgene that produces the protein that has insecticidal action was obtained from a bacterium, Bacillus thuringiensis (Bt) and is often referred to as a Bt hybrid.

YieldGard^® Corn Borer _ This transgenic trait (also of Bt origin) provides resistance to European corn borer, southwestern corn borer, southern cornstalk borer and fall armyworm and moderate resistance to corn earworm and common stalk borer.

LibertyLink^® _ Hybrids with this transgenic trait are resistant to Liberty^® (glufosinate) herbicide. This trait is often combined (stacked) with one of the Bt traits. Liberty^® controls small annual weeds.

Clearfield^® _ Corn hybrids with this non-transgenic trait are resistant to imidazolinone herbicides.

Roundup Ready^® _ This transgenic trait provides crop safety to over-the-top applications of Roundup^® and other brands of glyphosate herbicide.

YieldGard^® Rootworm _ Hybids with this transgenic trait (Bt origin) have resistance to corn rootworm larvae. YieldGard Plus^® hybrids contain both the YieldGard^® Rootworm and the YieldGard^® Corn Borer traits.

Grain produced from hybrids with the above traits can be used in the United States, Canada and Japan. However, YieldGard^® Rootworm, Roundup Ready^®, Herculex I^® and YieldGard^® Corn Borer and LibertyLink^® stacked with another trait are currently (2004) not approved for use in the European Union.

The national Corn Growers Association maintains a current listing of traits and their export status, known as "Know Before You Grow," on the Internet at: www.ncga.com/index.shtml.

Other factors

Other factors to consider when selecting a corn hybrid include: stalk strength and lodging resistance, resistance to stalk rots and other diseases, tolerance/resistance to insects, reaction to drought stress, harvestability, test weight and dry-down.

Some corn companies characterize hybrids they sell as "flex" or "fixed" ear hybrids. Flex-ear types are promoted as hybrids that are able to adjust yield components during the growing season to take better advantage of optimum growing conditions. All corn hybrids can compensate or flex yield components during the growing season by adjusting the number of ears per plant, number of kernels per row and kernel size, depending on environmental conditions. Nevertheless, using hybrids that are known to do well under low populations (these data are not always available) may be advantageous in the areas of the state where low plant populations are recommended due to moisture limitations.

Corn Production Practices

Date of planting

Optimizing corn yields starts with planting early. For most of the state, early means May 1. If you are growing a large area of corn, planting should start prior to May 1. Early planting is recommended because the risk of fall frost damage to crop yield and quality is greater with each day planting is delayed, and is more likely to be more harmful than early-season frost damage.

Even though corn seeds germinate optimally in soils that are warmer than 50 degrees, having the seed in the ground before these temperatures are reached often enables earlier emergence. If planting is delayed beyond May 20 in the northern part of the state, an alternate crop should be considered. For the southern part of the state, switching to a hybrid that is five to seven days earlier is recommended for plantings after May 20 up until the first week of June. Crop insurance coverage may not be available beyond certain dates and should be considered before planting too late in the season. Planting earlier than April 20 can also be risky as soil temperatures in most years are too low to allow germination until well into May.

Seedbed preparation

For rapid and uniform emergence, corn requires a soil that is warm, moist, well-aerated and fine enough for good soil-seed contact. In addition, an ideal seedbed should prevent wind and water erosion, conserve moisture, control weeds and improve or preserve soil tilth. Corn seed can be successfully sown using a wide range of pre-seeding tillage practices. Reduced- or zero-tillage practices, which help reduce wind and soil erosion and conserve soil moisture, are gaining in importance in the state.

Regardless of what pre-seeding tillage is employed, good soil-seed contact is critical to ensure uniform germination and emergence. Avoid tilling soils that are too wet and that will form clods, or making excessive trips across the field that may leave the seeding zone dry. Press wheels should be adjusted so the seed is in contact with soil on all sides.

In reduced-tillage systems, some residue removal over the seed row can increase soil temperatures. When planting into heavy residue, make sure the cutting coulter runs deeper than the disk openers and that it actually cuts the residue so residue is not simply pushed into the ground, causing "hair-pinning" which can negatively affect seed-to-soil contact and increase the rate of soil drying in the seed zone.

Row-width

Corn is most commonly grown in rows of 30 inches. There is a trend in the Corn Belt toward using narrower spacings. Recent data suggest that in the higher-yielding regions of the state, narrower rows do offer a slight advantage in yield (3-8 percent is most commonly reported in other states). This yield advantage is not always consistent and in areas of the state that are prone to drought, wider rows may offer an advantage. Before going to narrow rows, consider the cost of new equipment, the amount of area you plant to corn and the yield potential on your farm.

Plant population

Plant populations should be based on available moisture, potential rainfall during the growing season and soil type. The cost of seed should also be considered when determining the plant population. Populations of 14,000 to 20,000 plants per acre are recommended in low rainfall areas and on light sandy soils where yield expectations are below 100 bushels per acre. Populations of 24,000 to 32,000 plants per acre are recommended in higher rainfall areas and 28,000 to 32,000 plants per acre for corn grown under irrigation. The seeding rate should be 10-15 percent higher than the desired harvest populations. See Table 2 as a guide for estimating plant populations at various row-width spacings.

Count the number of plants in the row length and multiply by 1,000 to determine the number of plants per acre.
 

Table 2. Estimation of plant population on a per acre basis.        

Example:  20 plants counted in a 17.5-foot row length of 30-inch row spacing = 20,000 plants per acre.

Planting depth

In most circumstances, corn should be planted 1.5 to 2 inches deep. Planting too shallow can cause unevenness in emergence if the soil surface dries out before all seeds imbibe sufficient water to germinate. Planting too deep will delay emergence as soil temperature decreases with depth. Shallow planting also causes the early crown (or nodal) roots to be shallow and not properly located to supply the corn plant with nutrients and water. Make sure the packer wheels are adjusted so there is good soil-seed contact. When the soil surface is dry and rainfall is uncertain, consider planting to a depth where uniformly moist soil is found, even if it is deeper than two inches.

Fertilizer Requirements

Fertilization should be based on soil tests and yield goals. Corn nutrient uptake will be approximately 1.5 pounds of elemental nitrogen (N), 0.5 pounds of phosphate (P₂O₅) and 1.2 pounds of potash (K₂O) to produce one bushel of grain corn. A large proportion of this is normally supplied by organic matter and the mineral portion of soil. If the soil cannot supply enough, the supply has to be supplemented with nutrients from other sources.

Nitrogen is the nutrient that is most often lacking in corn production. Nitrogen may be applied before planting, at planting time, as a side-dressing after corn has emerged and through an irrigation sprinkler system. Fall applications of N are not recommended on sandy soils or soils subject to flooding. The formula for N recommendations is:

Yield Goal X 1.2 less soil test nitrate-N to 2 feet in depth, less any previous crop credit from legumes or other crops.

(See previous crop credit table in NDSU Extension Service publication SF-882, "North Dakota Fertilizer Recommendation Tables and Equations," revised 2003).

Site-specific farming methods, especially yield mapping, will aid in determining realistic yield goals between and within fields.

Phosphorous is the nutrient next most likely to be deficient. Phosphorous (P) soil test levels are optimized at 12 parts per million (ppm), and potassium (K) soil test levels are optimized at 150 ppm to maximize corn yields (see NDSU Extension Service publication SF-882 "North Dakota Fertilizer Recommendation Tables and Equations," revised 2003).

Starter fertilizer is defined as plant nutrients applied with the planter in a band with the seed or in a side band, which separates seed and fertilizer by at least an inch. The entire recommended fertilizer rate can be safely applied in a band two inches to the side and two inches below the seed. Under cool, wet conditions, no-till or ridge-till systems, starter fertilizer offers advantages over broadcast P and K. Fertilizer placed with the seed should not exceed 10 lb./acre N + K₂O in medium- or heavier-textured soils with normal soil moisture.

Potassium is most likely low in sandy soils with lower cation exchange capacity (CEC). However, recently K deficiencies have also been seen more regularly in South Dakota and Minnesota in heavier textured soils, especially in no-till systems.

Potassium deficiencies will be expressed as yellowing of the lower corn leaf margins, with the mid-rib being the last area of the leaf to lose greenness under severe K deficiency conditions.

Application of K with the seed is limited by potential salt injury. Higher levels of K can be applied as a side-band or in a broadcast application. Our most common K source is KCl (0-0-60), which also contains chloride. Responses to chloride in corn have been documented in New Jersey and Kansas. Work has not been conducted in the immediate region to date to confirm that attention to chloride levels would benefit North Dakota corn growers.

Zinc (Zn) is sometimes deficient for corn in this region. The DTPA soil test for Zn is most commonly used in North Dakota. However, composite soil sampling may miss deficient areas. Lower Zn levels are most common on uplands and slopes and higher levels are more likely in depressional areas. Deficient corn is stunted, with yellow to white stripes in upper leaves. Rescue applications of liquid Zn fertilizers are helpful. However, it may be a better plan to apply Zn prior to, or at, seeding. Zinc sulfate or other water soluble dry granular products can be applied in a broadcast application to increase soil test Zn levels.

These applications are effective for several years, compared to banded applications of chelates or ammoniated Zn products. Zinc chelates or an ammoniated Zn product can be mixed with liquid fertilizers, such as 10-34-0 and applied with the seed or in a side-band at planting. If applied with the seed, limit the application to 1 quart/acre on most soils, but reduce the rate of ammoniated Zn to a maximum of 1 pint/acre in dry, sandy soils. Application of starter P may magnify Zn deficiencies if Zn is not added to the starter.

Excessive fertilizer use, especially nitrogen and phosphorus, has potential to degrade ground and surface water quality. Establishing realistic yield goals and basing fertilizer applications on soil sample analysis will help preserve water quality.

Weed Control

A combination of cultural, mechanical and chemical methods may be necessary for consistently effective weed control in corn. In early spring, recently emerged weeds can be controlled before planting with secondary tillage. A rotary hoe or a light spring tooth harrow can be used to control weed seedlings when corn has emerged. Cultivation between the rows should be done soon after weeds emerge or on an as-needed basis.

In some cases, little if any cultivation is required if herbicide combinations are properly applied and activated. Corn producers have numerous herbicides for selective weed control in corn grown in conventional, minimum-till or no-till production systems.

Weed competition is a major source of corn yield loss. To prevent yield loss, weeds must be removed soon after corn emerges. Populations of grass weeds are usually high and if not removed within the first three weeks can stunt corn growth and reduced yield. Studies indicate that if weeds are removed two to three weeks after corn emergence, yield reductions are unlikely. Also, if fields are kept weed-free for four or five weeks after emergence, most weeds that emerge later will not significantly reduce yield.

Late-germinating weeds may produce many seeds, cause harvest problems and reduce crop quality, however. Weeds that germinate early and/or have large plant architecture, like common cocklebur, common ragweed, sunflower and marshelder, are very competitive. Wild oat, kochia and wild mustard can be very competitive, especially in dry conditions. Redroot pigweed and common lambsquarters are less competitive than the large-seeded weeds listed above but when present in high densities an infestation can severely reduce yields. On a plant-for-plant basis, small-seeded and small architecture plants like annual grasses, nightshade and wild buckwheat are the least competitive. Corn yield reduction based on different weeds and weed densities is listed in Table 3.

 

Table 3. Weed interference and corn yield.
	Corn yield reduction (%)
	1	4	8	10
Weed species	-number of weeds/100 ft of row-
Foxtail spp.	15	60	175	400
Velvetleaf	10	20	40	50
Lambquarters	12	50	125	150
Pigweed spp.	12	50	125	150
Cocklebur	4	16	34	40
Shattercane	6	25	75	100
Yellow nutsedge	400	-	-	-

Herbicide or herbicide combinations used should be based on weed species present, crop rotation, herbicide-resistant corn technology available, soil type and cost. Consider the economics and weed species when selecting the most appropriate control system for each field. Refer to the current issue of the NDSU Extension Service publication W-253, "North Dakota Weed Control Guide" (located at www.ag.ndsu.nodak.edu/weeds/w253/w253w.htm  on the Web) for more detailed information on corn herbicides, use of spray adjuvants and mixing recommendations.

Many corn herbicides are labeled for tank-mixing with other herbicides for broad-spectrum weed control. Several commercial corn herbicide mixtures are available. Consult the label for information on individual herbicides and a complete listing of all possible registered combinations. Herbicides suggested for specific weed control in North Dakota corn production are listed in Table 4 (pages 10 and 11).

Herbicide-resistant corn technologies are available. Lightning^® herbicide controls most annual grass and broadleaf weeds and can be applied only to Clearfield^® corn varieties. Lightning^® is an ALS herbicide and will not control ALS-resistant kochia and other ALS-resistant weeds. Liberty^® controls most small annual grass and broadleaf weeds and can be applied only to Liberty Link^® corn varieties. Liberty^® is a contact type, nonselective, nonresidual herbicide and should be applied to small weeds for the most effective weed control. Liberty^® will control all ALS-resistant weeds.

Glyphosate controls most annual and perennial grass and broadleaf weeds and can be applied only to Roundup Ready^® corn varieties.

Glyphosate is a systemic, nonselective, nonresidual herbicide and may require two sequential applications or use after a foundation soil-applied herbicide program. Other glyphosate resistant crops can be grown in North Dakota, such as Roundup Ready^® soybean and canola.

Controlling volunteer Roundup Ready^® corn in Roundup Ready^® soybean maybe require use of a postemergence grass herbicide, such as Assure II^® or Select^® in addition to glyphosate. Public nonacceptance of Roundup Ready^® technology may limit market potential. Plan ahead and secure an available selling market before growing a herbicide-resistant corn variety.

Table 4. Herbicides for Weed Control in Corn