Meeting Corn Grain Purity Standards for Specialty Markets

Crop Insights written by Steve Butzen1 and Morrie Bryant2



  • Farmers have contracted to produce white, waxy or other specialty corn types for decades. Non-GMO corn is a relatively new niche market opportunity.
  • Countries have imposed their own unique purity standards for non-GMO grain; growers must clearly understand the purity requirements for their market.
  • To meet purity standards, growers must take additional steps during planting, growing, and harvesting the crop; and drying, storing, handling and transporting the grain.
  • At planting, keeping good records, establishing adequate isolation and cleaning planting equipment and seed tenders are the steps needed to help meet purity standards.
  • To prevent volunteer corn in a specialty crop, harvest the preceding corn crop in a timely manner, rotate away from corn, and/or use tillage or herbicides when appropriate.
  • At harvest, inspect and clean the combine, grain cart and truck. Harvest a number of “border” rows and segregate that grain to increase the purity of the rest of the field.
  • Clean dryers and grain bins thoroughly of all residual grain between commodity and specialty production, then clearly document which hybrid is stored in the bin.
  • Allow conveying systems (augers and elevators) to run empty between loads of different grain types, and empty the auger sump or pit of residual grain.


Growing corn for “specialty” or “niche” markets provides an enhanced income opportunity for farmers. The higher price commanded by these markets is due to the additional management and risk associated with producing specialty grains. Additional management is required to meet the purity standards of these markets; the risk is typically that if purity standards are not achieved, the crop may have to be marketed in traditional commodity channels with no pricing premium. Specific contractual obligations may present another layer of risk. This Crop Insights discusses specialty corn markets (with particular focus on non-GMO markets), purity standards for these markets, and management practices to help achieve the purity requirements.

Harvesting specialty corn grain.

Non-GMO Corn Production

A corn hybrid containing a “biotech” or “transgenic” trait is often referred to as a “Genetically Modified Organism,” or “GMO.” Following their introduction in the mid-1990s, GMO hybrids were adopted by farmers at an unprecedented pace. Today, approximately 95% of the U.S. No. 2 yellow corn crop is grown utilizing biotech or transgenic traits. The remaining 5% of the crop, generally referred to now as the “conventional” or “non-GMO” corn market segment, has essentially morphed into a new niche market for corn.

Though non-GMO production is one of the newest niche market opportunities, specialty corn production is not a new concept; many farmers have contracted to produce white, waxy or other specialty types for decades. In general, the principles of achieving purity standards for 1 type of specialty production apply to other types as well; however, non-GMO production presents some unique challenges. This is primarily because countries have imposed their own purity standards for non-GMO grain, and these standards differ significantly from one another. In addition, non-GMO production for export to the European Union has much more stringent purity requirement than other markets. Thus, the non-GMO market can be best thought of as a series of niche markets, each with its own unique purity requirements.

Asian and European Non-GMO Markets
The primary driver for non-GMO corn has been and remains the Asian export market. Japan and Korea are the 2 major US export customers for this grain. Both countries have GMO label laws in place that require notice on a product label of the presence of biotech traits. Many Japanese and Korean consumer product companies, particularly food companies, choose to source non-GMO corn in order to avoid putting such a notice on their products.

Japan defines non-GMO corn as that corn which is a minimum of 95% corn of no detectable traits. So, Japan has set a 5% threshold of tolerance for unintended or “adventitious” presence (AP) of biotech traits in the corn grain they import. When non-GMO corn is originated in the United States, these tolerance thresholds are risk-managed and usually trade at 3% levels. South Korea, on the other hand, uses a minimum standard of 97%, thus a threshold of tolerance for AP of 3%. These programs often trade at the point of origination at a 2% threshold of tolerance. Finally, Europe has the most restrictive standards for non-GMO, employing a 99.1% level of no detectable GMO traits, or a 0.9% threshold of tolerance for the adventitious presence of these traits.

Percent adventitious (unintended) presence allowed in various specialty corn markets.

Figure 1. Percent adventitious (unintended) presence allowed in various
specialty corn markets. (Examples of AP include yellow kernels in white corn
production, normal starch in waxy production, and any GM trait in production
for non-GMO markets.)

United States Non-GMO Markets
A non-GMO domestic market also exists in the United States, although it is relatively small. There are growers and consumers alike who demand choice and prefer to not utilize biotech traits. The primary challenge in this market is that there is currently no standard definition of “non-GMO”; rather, it is typically whatever the particular market wants it to be. This ambiguity presents an obvious challenge for growers; if they fail to clearly understand how their particular market defines “non-GMO”, they could be disappointed when they deliver corn. This applies to all non-GMO production, not just production for US markets. Growers must know for certain if the threshold of tolerance for GMO traits is defined in the contract as 3%, 2%, 0.9%, or some other standard. Clearly understanding these “rules of engagement” is necessary to make the best possible decision about participating in the non-GMO market opportunity.

Achieving Purity Standards for Specialty Corn

After carefully reviewing the purity standards mandated for the specialty crop being grown, producers must implement appropriate production practices to achieve those standards. This includes taking additional steps during planting, growing, and harvesting the crop; and drying, storing, handling and transporting the grain.

Planting the Crop
At planting, record-keeping, isolation and equipment clean-out are the steps generally recommended to help ensure the grain ultimately meets required purity standards.

Record-keeping may be simple or sophisticated, depending on the technology available and grower expertise. As-planted (GPS-tagged) records that are transmitted in real time and backed up for safe-keeping are the most foolproof way to document planting. Electronic “notes” recorded on a smart phone or pad and also backed up in the cloud can be equally effective. Lastly, handwritten notes may still be adequate, but lack the safety advantages inherent in backed-up electronic field records. Taking a picture of handwritten notes with a smart phone can lessen the risk of losing these records. Some contracts may require specific forms of documentation during the production of the specialty crop, including at planting. Be sure you are aware of any such contract requirements.

Isolation: Because corn is a cross-pollinated crop and its pollen is wind-dispersed, providing adequate isolation is at the very core of specialty corn production. In fact, the ability to sufficiently isolate the crop from other corn fields is often the deciding factor when considering specialty production. The degree of isolation required is, of course, closely tied to the level of purity targeted. For many end uses, the buyer will provide isolation guidelines to the grower. These guidelines will always take into account the distance and direction (upwind or downwind) of nearby corn fields, and may also consider the type of corn (e.g., dent or sweet) in those fields. A commonly recommended isolation distance for some types of specialty corn production is 660 ft., but that distance could double when purity requirements are extremely high. Be sure to clearly understand the isolation distance needed to achieve your desired level of purity.

Inadequate isolation distance can often be overcome by using a number of rows of the specialty crop as a “buffer,” segregating the buffer grain at harvest, and selling it as commodity grain if it doesn’t meet the purity standards. “Time isolation” can effectively add to distance isolation. Time isolation involves staggering the planting dates of the specialty and nearby corn to create a pollination “differential.” This practice may be risky if employed as the primary means of isolation, as crop pollination timing interacts with the growing environment and is not completely predictable.

Equipment cleanout at planting: A basic tenet of specialty corn production is cleaning equipment to remove kernels of contaminating (non-specialty) seeds and grain. Planters are reservoirs for contaminating seeds of previously planted hybrids. Each make of planter is different, but a thorough cleaning usually involves removing seeds from each individual seed metering unit in addition to the seed hopper(s). The planter owner’s manual should provide tips on proper cleanout procedures, which may also be available online. Growers may also want to check for any videos demonstrating planter cleanout at or other websites. Seed tenders, including the box and auger, must also be cleaned to prevent mixing or commingling of seeds.

Growing the Crop
In most cases, there are no visual differences between corn hybrid plants, whether they are GMO, non-GMO or any number of other specialty grain types. That makes it difficult or impossible to identify and destroy unwanted plants prior to harvest. Thus, all possible steps should be taken to prevent possible inclusion of off-type seeds at or prior to planting.

Some unwanted plants in a specialty corn field are not sourced from the planting equipment; rather, they are volunteer corn plants from ears or grain left in the field from previous crops. When volunteer plants grow from a dropped ear of corn, they usually grow in a thick bunch that precludes the development of grain on any of the volunteer plants. However, tassels may be produced on some plants, leading to pollen mixing with the new crop. Just like pollen drifting in from a nearby field, this pollen mixing would reduce the purity of the specialty grain. Thus, all measures should be taken to prevent volunteer corn in a specialty crop, including timely harvest of preceding corn, rotation away from corn, and use of tillage or herbicides when appropriate.

Harvesting the Crop
Harvest presents an opportunity to increase the purity of the specialty crop, as well as a risk of decreasing it. Harvesting a number of “border” or “buffer” rows from the perimeter of the field and segregating that grain can increase the purity level in the remainder of the field. For example, harvesting 16 to 24 rows from the windward (usually south or west) side of a field may be recommended when there is a corn field nearby in that direction, especially if the isolation distance is at or below the suggested minimum.

The risk of decreasing crop purity comes from the chance that significant off-type grain is still present in the combine, grain cart or truck. Inspecting and cleaning the grain cart or truck is a rather simple and basic process; doing the same for the combine is significantly more complex.

Combine clean out: If the combine has been thoroughly cleaned before storing the previous winter, harvesting the specialty field before any others can save a cleaning. Otherwise, additional steps are likely needed – studies have shown that as much as 1 to 2 bushels of grain may remain in the combine, even after running the unloading auger empty for a full minute.

The first step in combine clean-out is to determine what level of purity is needed. For some grain uses, simply “flushing” the existing grain will be adequate. This is accomplished by harvesting a load or partial load of the specialty hybrid and using that load for commodity grain.  While negating any premium opportunities for those bushels, this method of clean-out may still be much more cost-effective than labor-intensive cleanout procedures.

Some types of specialty production (e.g., non-GMO production for European markets), may require a more thorough combine cleaning. Details for systematically cleaning the entire combine vary by brand and model. Consult your operator’s manual for manufacturer instructions, or search for instructions or videos online. Then follow a systematic plan to clean specific areas in the machine, usually going from top to bottom and entry to exit. Be sure to conduct cleanout procedures with the utmost safety in mind, including blocking the head and removing the key when workers will be in harm’s way. Cleanout may involve running the machine 1 or more times during the process – be sure all workers are clear of the machine.

Drying and Storing the Grain
Clean dryers and grain bins thoroughly of all residual grain. Growers generally do a good job of cleaning these areas between crops, such as corn and soybeans. Applying the same discipline to cleaning between commodity and specialty production may be needed to meet purity standards for some grain uses.

In addition to cleaning, labeling and record-keeping are important to maintain the identity of grain in storage. Clearly document the hybrid, cleaning procedures and other information according to the intended end use or contract requirements.

Handling and Transporting the Grain
The existing commodity grain handling system is designed to store, transport, and distribute billions of bushels of crops. Growers, grain handlers, and processors did not have special segregation of crops in mind when they built bulk-handling systems. Consequently, there are numerous ways that adventitious presence may occur during grain handling and transport. Commonly referred to as "mechanical mixing" or commingling, these include mixing of grain in harvesting, handling (conveying systems), hauling or in processing equipment or storage facilities.

Conveying systems: Auger and elevator contamination can be minimized by allowing conveying systems to run empty between loads of different grain types. Also, the auger sump or pit should be emptied of residual grain. If additional purity is needed, this can be followed by flushing the system with the new grain and placing the flushed grain in a mixed grain bin.

Grain Cart/Trucks: Clean all obvious surfaces where grain may reside, including horizontal ridges inside of the grain cart. The vertical auger sump in grain carts may have a clean-out shield at the base.

Maximizing Genetic Purity of Specialty Corn

  • If at all possible, discuss planting intentions with neighbors and try to work together to maximize each other’s grain marketing options.
  • Thoroughly clean all other seed out of the planter before planting.
  • Plant on land that did not have the specific hybrid type you are trying to isolate against grown the previous year.
  • Plant corn in blocks as large as possible, rather than in several smaller fields.
  • Maximize isolation distances from all other corn. Acceptable distances may vary from 24 rows to as much as ¼ mile (1,320 ft.) or more separation, depending on target purity level, prevailing winds, planting date, hybrid characteristics and general weather conditions.
  • Exact isolation guidelines will depend on purity standards for acceptance of grain. However, the greater the isolation distance used, the greater the chance of maximizing purity.
  • Even under the best conditions and practices, the biology and logistics of corn production and pollen movement make 100% purity nearly impossible to attain.
  • To minimize prevailing wind effects on pollination, plant corn hybrids you are trying to isolate to the west or upwind from all other corn hybrids.
  • Staggered planting can also be used to help minimize cross-pollination. The sequence and timing of planting will depend on a hybrid’s flowering characteristics and maturity.
  • Harvest outside rows of the field where you are trying to maximize purity and segregate this grain for other uses.
  • Thoroughly clean combines, trucks, wagons, grain augers, dryers and storage units when switching from one type of corn to another.
  • Consider keeping samples of the seed, harvested grain and delivered grain. Preserve the samples until the grain has met all identity and quality standards of the buyer.
  • Remember that achieving 100% purity is virtually impossible in seed or grain production. These management practices are designed to help maximize production purity but do not guarantee absolute purity.

1Agronomy Information Consultant, DuPont Pioneer

2Sr. Marketing Manager, DuPont Pioneer

PIONEER® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.

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