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Effects of Corn Stover Removal on Nutrient Management

KEY POINTS Harvested corn stover can be used for:

 

Introduction

The harvesting of cornstalk residue (corn stover) after grain harvest has long been used for bedding, cellulosic ethanol, and as an additional forage source for livestock, especially in years when forage production has been short due to drought. Removing stover to reduce residue levels is emerging as another reason after continuous, high yielding corn production situations. The amount of corn stover produced is greatly proportional to the amount of grain produced. For every 40 bu/acre of corn produced, one ton of residue
is produced. For example, a 240 bu/acre field produces about six tons of residue while an 80 bu/acre field produces about two tons of residue.

 


Figure 1. Corn Stover Bale. Photo courtesy of Jennifer Rees, Extension Educator, University of Nebraska.

 

The percentage of stover harvested depends on several factors including the amount of grain harvested, soil organic matter, climate, soil type, slope of the field, crop rotation, and the tillage used before the next crop in planted. When comparing stover to silage harvesting, there are several differences. Stover removal is often much less than the 90 to 95% of the above ground plant harvested for silage, depending on silage cutting height. The nutrients removed with silage harvest is well documented, while understanding the nutrients removed with harvesting stover is more complicated due to a later harvest and the amount of biomass removed. However, in many silage production operations, manure from the livestock operation can be applied to the harvested fields. This can allow for the replacement of nutrients lost from the corn crop harvested as silage. When comparing grain harvest plus some stover harvest to a silage harvest system, less biomass carbon (C) and less total plant nutrients are removed.

One of the most important issues associated with stover used for cellulosic ethanol production is that it must have low soil contamination. This is why energy companies often recommend a partial stover harvest of 20 to 60 percent.

The removal of corn stover is also being considered as a viable and sustainable management option in high yield, minimum or no till, continuous corn environments. This is a situation that is more likely to occur in irrigated western corn growing regions where high corn yields can occur year after year. These are production systems where high grain yields produce high levels of residue and are in environments where residue breakdown by biological processing is slow due to low levels of moisture in the winter and spring. This high level of residue production and build up is multiplied when there is no or very limited tillage to help with residue breakdown. The major problems caused by high levels of corn residue, still on the soil surface at planting time, are plugged planters, emergence issues due to poor soil to seed contact, and lower soil temperatures.

These situations have shown an increased yield response to stover removal but do not require all the stover to be removed every year. 50 to 60 percent stover removal each year is often enough to greatly reduce the issues at planting time while helping to prevent most wind and water erosion concerns on fields with limited slope of no more than two to three percent along with maintaining good soil tilth.

Stover Nutrient Content

When considering the impact of nutrients removed in harvested stover, it is important to know how the interactions of crop rotations, corn yield levels, and the amount of plant matter removed can impact long-term soil health. The removal of nutrients directly affects the recycling of nutrients which affects the amount of fertilizer needed to grow the following crops. Determining the amount of nutrients in corn stover is complicated because nutrients, especially potassium (K), can be leached out of plant tissue from maturity through grain harvest, and continue until the stover is harvested and removed from the field. This means that nutrient concentrations per ton of stover removed, can vary considerably depending on the rainfall amount and pattern from plant maturity through time of grain harvest and until the stover is harvested.

There are numerous resources to help estimate the nutrient removal associated with stover harvest. One good resource is the Corn Nutrient Composition at Plant Maturity by Plant Part (Table 1). These averages help a farmer understand the differences and similarities of the nutrient composition by plant part at maturity, which is important when comparing removal by harvest type. The vegetative plant parts column which includes stalks, leaves, tassels, ear shanks, and husks and when combined with the cobs estimates the pounds of nutrients removed per ton of harvested stover on a dry matter basis.

Carbon (C) will be removed with a grain harvest, but when returned to the soil is important to maintain soil organic matter. Carbon levels are nearly the same when comparing nutrients removed by each plant part on a pounds per ton /dry matter basis. However, the total amount of C removed by grain harvesting is about the same amount as the vegetative and cob amount combined (100% stover harvest). Yearly C removal levels do not include C in the root system which is not affected by any type of corn harvest.

Nitrogen (N) is the next nutrient to be considered when stover is removed. Since most of the N is removed with the grain harvest, the N in the vegetative tissue and cob need to be considered with a different approach. Much of the N is tied up in high C:N ratio tissues that need to be broken down by soil organisms before it becomes available for the next crop. In the short term, this nutrient tie-up can result in N being unavailable for the next crop, especially in high yield corn production environments. In recent years, there has been an increased focus placed on C and N removal because of their influence on the sustainability of the soil resource and water quality in all types of production systems.

The last nutrient of importance is potassium (K). Potassium can have a high nutrient per ton concentration in the vegetative tissues that are removed with a stover harvest. Potassium is soluble in mature plant parts; therefore, in environments with high rainfall after plant maturity and before the stover is harvested, much of the K can potentially leach out before stover harvest. This is why there can be a high level of variation in the amount of K removed when stover is harvested. This depends greatly on the timing and the amount of rainfall after plant maturity and should be managed accordingly.

Finally, phosphorus (P), calcium (Ca), magnesium (Mg), sulfur (S) and micronutrients (zinc (Zn), manganese (Mn), copper (Cu), boron (B), iron (Fe)) are in low levels and are often not a concern when considering a stover harvest option.

 

Table 1. Corn nutrient composition at plant maturity by plant part.
Nutrient Grain Vegetation Cob
lb/ton (DM)
C 795 840 797
N 24 12 10
P (P2O5) 12 3 –
K (K2O) 8 22 –
Ca 2 9 –
Mg 2 6 –
S 2 1 –
Zn 0.030 0.031 –
Mn 0.006 0.069 –
Cu 0.004 0.015 –
B 0.009 0.015 –
Fe 0.047 0.281 –
*Corn nutrient composition at plant maturity by plant part. Sawyer, J.W. and Mallarino, A.

 

Change in Nutrient Content with Time

Concentrations of P and K contained in corn stover decrease after maturity. Most of this decrease occurs after black layer formation through maturity.2
After grain harvest, K declines consistently in stover left in the field overwinter; however, the loss can be accelerated by rainfall anytime from maturity until the next crop is planted in the spring. Concentrations of P in the stover stay about the same in the fall and then decreases only slightly during the winter. The potential for large change in stover K concentration from harvest until early spring makes estimates of K removal with stover harvest complicated.

 

Corn N, P, and K Fertilization after Stover Harvest

Knowing how much P and K is removed with any type of corn harvest is important to help maintain desirable soil-test values and is included in P and K fertilizer recommendations for corn grain production. Although N removed with corn grain production is not used to determine the N fertilizer rate for the next crop, it is reflected in traditional Corn Belt N rate recommendations. In many western corn production areas, fertility recommendations for the following corn crop are made using a winter soil fertility test along with yield goals. Corn nutrient removal estimates are not used for the recommendations. This type of fertility recommendation reflects less nutrient recycling due to less organic matter in the soil.

Most N response trials have not included harvested stover in the trials; therefore, studies with and without stover should be reviewed to help determine the short and long-term effects of stover removal on maximum economic corn yield potential. One study from Iowa, looked at two sites where continuous corn rotations were evaluated for the long-term effect of both partial stover removal and full stover removal on the fertility recommendation needed to reach maximum economic yield in the next-year corn crop. This study determined that the economic optimum N rate for partial removal (about 30 to 40% stover harvest) was 20 lb N/acre less than when all the corn residue was returned to the soil. This same study determined that economic optimum N rate for full stover removal (about 90% stover harvest) was 40 lb N/acre less than when all the corn residue was returned to the soil.

These numbers seem backward as more N is being removed with the higher levels of stover harvest so it would be expected more applied N would be needed to grow the next corn crop. This type of response can be expected when high levels of high C:N ratio plant matter is added back to a soil. This response is caused by the inability of soil microbes (bacteria, fungi, protozoa and actinomycetes) to process (recycle) residue back into plant nutrients fast enough to meet the nutrient needs of that crop during the next growing season. Along with the fact that these same organisms are tying up soil N is why a higher N application is needed to maximize corn yield potential when stover is added back into the soil.

Another source shows estimates for the average nutrient concentrations being removed per dry ton of corn stover removal:

Nutrient amount (lbs/ton) x fertilizer price ($/lb) = Value of Nutrients in Stover ($/ton).

Using the values above, this equation can be used to calculate the value of each nutrient lost in lbs/ton of stover harvested by using the current fertilizer price for each nutrient.

 

Conclusions

When considering if harvesting corn stover is right for your production system, several factors that influence soil quality should be considered. This decision may be a field-by-field decision due to the amount of stover produced, field slope, soil type, organic matter, tillage type, and crop rotation. These factors can affect the potential for wind and water erosion along with the nutrient recycling capacity of each field. Corn stover left on the soil surface can help reduce the potential for wind and water erosion by creating a protecting layer. This is a factor that is affected by the amount and type of tillage used after harvest that can decrease the protective stover layer by incorporating it into the soil. No-till or limited till production systems allow for more stover to be harvested as it conserves the stover left on the soil surface. Cover crops can be used with a stover harvest system to help protect the soil surface

Soil organic matter (O.M.) and nutrient recycling are important soil quality considerations that need to be addressed before deciding if stover harvest is
an option for your operation. While soil O.M. is very important for productive soils, it is in a constant state of flux. By harvesting the corn stover there is less C available for the soil to convert back into new O.M. However, it appears that new O.M., that is created over time by many forms of decomposing dead plant matter is driven by living and decomposing roots.3 The C source associated with the roots, which is needed to sustain soil O.M., is not affected by stover harvest. By using minimum tillage along with limiting the amount of stover harvested to around 30 to 50% can often keep the C levels in most soil high enough to help sustain the O.M. needed for healthy soils. Higher corn grain producing fields produce higher stover amounts which can allow for higher stover removal levels while keeping enough to help protect the soil from erosion. When it comes to nutrient recycling, it is difficult for soils to recycle large amounts of high C:N ratio stover, especially in corn-on-corn rotations, rapidly enough for use by the following corn crop. This can cause a reduction in corn yield due to N that is tied up in the decomposing stover and not available for the next corn crop.

In many situations it comes down to economics, which varies annually by field depending on the many variables used to determine stover removal feasibility and value. Can the return from a stover crop create enough income to cover harvest costs, including the cost to deliver the stover to the end user, and storage along with replacing the nutrients lost by stover harvest. Most costs, which need to be included in a stover harvest economic analysis, are variable year to year, include fuel, equipment, labor, and fertilizer costs. While the value of stover used as a forage feed source, more in times of drought conditions, may be a very valuable resource for cattle feed on or off the farm.

Many corn production operations can successfully harvest stover when balanced with frequent soil testing and a good fertility program to monitor the affects to the soil over time. Like most production systems there are advantages and disadvantages for each system. Only when a farmer understands these limits and variables can an educated decision be made to decide if stover harvest is right for their operation.

 

Article Link

Source:
Rees, J., Schmer, M., and Wortmann, C. 2017. Corn stover removal: nutrient value of stover and impacts on soil properties. CROPWATCH. University of Nebraska-Lincoln. Institute of Agriculture and Natural Resources. https://cropwatch.unl.edu/2017/corn-stover-removal-nutrient-value-stover-and-impacts-soil-properties
Sawyer, J. E., and Mallarino, A. P. 2014. Nutrient considerations with corn stover harvest. PM 3052C. Iowa State University Extension and Outreach.
https://store.extension.iastate.edu/Product/Nutrient-Considerations-with-Corn-Stover-Harvest
Ertl, D. 2013. Sustainable corn stover harvest. Corn Stover research. Iowa Corn Promotion Board.
https://www.iowacorn.org/corn-production/research-and-patents/corn-stover
Legal Statements:
Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2024 Bayer Group. All rights reserved. 1213_72706.

Post Harvest Grain Storage Management

 

Causes of Storage Problems

First and foremost, grain should be dried to the proper moisture content before storage to help avoid grain quality issues. The recommended moisture contents for corn and soybean at various storage periods are shown in Table 1. Corn stored at 19% moisture content and a starting temperature of 75 °F can lose a market grade in approximately five days if the aeriation in the storage facility is not working and the temperature of the grain increases.

 

Table 1. Maximum percent moisture content for safe corn and soybean grain storage.
Grain and storage time Maximum moisture content for safe storage
Shelled Corn:
Sold by Spring 15.5%
Stored 6-12 months 14%
Stored > 1 year 13%
Soybeans:
Sold by spring 14%
Stored up to 1 year 12%
Stored > 1 year 11%
Moisture percentages for good quality grain. Reduce 1% for poor quality grain (drought, disease, frost, harvest damage, etc.) 1McKenzie, B. and Van Fossen, L. 1995. Managing dry grain in storage. Midwest Plan Service. AED-20. Purdue University.

 

Other causes of grain quality issues during storage involve storage management, and include:

 

Grain Cooling and Aeration

If the grain has dried to the proper moisture content, improper temperature management is the primary reason for spoilage. When the grain temperature in the bin does not remain consistent, moisture in the bin can migrate and accumulate in areas and result in grain spoilage. Spoilage from moisture migration can occur whenever temperatures vary in the bin, but it is more common when the grain is stored warm and outside temperatures are cold. Without proper temperature management, the well-insulated grain and surrounding air inside the bin can retain the initial storage temperature (50 to 80 °F) and consequently lead to large discrepancies between the outside temperature and the temperature of the stored grain. Regardless of the time of year, grain should be maintained within 15 to 20 °F of the average monthly temperature.

Aeration is used to control grain temperature by moving air through the grain. In general, aeration should not be used to dry grain even if using it may cause the moisture content of the stored grain to change slightly. Aeration is used to cool grain in the fall or to help warm it in the spring. Cooling grain in 10 to 30 °F increments for winter storage should reduce the likelihood of mold growth and insect reproduction.

The cooling or warming zone, the area of the grain that changes temperature, follows the aeration through the bin. One cooling/warming cycle is the amount of time needed to move a cooling/warming zone completely through the bin. Once a cycle has begun, the fan should operate continuously until the zone moves completely through the bin.

On-farm storage systems may be equipped to move air between 1/10 cfm (cubic feet of air per minute)/bu to over 1 cfm/bu (0.003 cubic meter of air per minute to over 0.03 cmm/bu). The rate depends on the bin type, air distribution system, desired storage moisture percentage, and proper management procedures. The time it takes to complete a full cycle depends on the aeration rate and time of year, and can be calculated with following formulas by season:

 

Grain Checks and Observations

Taking multiple grain samples when filling the bin and during storage can help account for variable moistures throughout the bin and reduces the risk of storage molds. Use the highest moisture content value to determine management options that can further reduce the risk for storage molds, hot spots, and spoilage. Averaging sample values may not adequately address pockets of grain with higher moisture content.

When temperatures are quickly changing in the fall and spring, stored grain should be checked weekly. Checks can be reduced to every two or three weeks when temperatures are more consistent and lower throughout the winter.

Keep an eye on the surface conditions, temperatures, and grain condition, and be mindful of different smells both in the grain and exhaust air. Grain that is crusting, wet, slimy, icy or frosty, or warming could be spoiling. Condensation or frost on the underside of the roof, hatches, and vents on a cold day almost always indicate a moisture migration problem. If crusting occurs, stir the surface to break up the crust or, if severe, remove the spoiled grain.

Once the grain is cooled, continue checking exhaust air for smells to help identify grain that could be spoiling. Regardless of the season or weather, if signs of heating or hot spots are detected, run the fan continuously until no further issues can be detected. If hot spots can’t be remedied with aeration, grain may have to be removed, cleaned, dried, or even sold. It may be better to sell at a lower price than to allow an entire bin to go out of condition.

 

Managing Stored Grain During Fluctuating Temperatures in the late Fall and Winter

Be aware of the major daily temperature fluctuations in your area. Cool (30 °F), moist mornings are typical during the fall and winter, and temperatures can rise throughout the day into the 50’s, 60’s or even 70’s °F. Parts of the country experience these temperature fluctuations on a regular basis. Continuously running fans during this type of temperature variation can lead to over drying or rewetting the grain due to the fluctuations in temperature and dewpoint.

A controlled and automated grain management system constantly measures and assesses these conditions, and only pushes air through the bin when the air is the appropriate humidity. Trying to do this manually is a very difficult task. As a result, you may notice your automated system running for a few hours in the morning and again in the late afternoon. This avoids the over-drying and rewetting that would occur if the fans were running all day.

Another important thing to consider is that automated systems can also cool grain. Some growers may have their grain come in at optimal moisture but will still need to cool it in order to increase its storage life. The warm and dry air available at certain times of the day may not accomplish this, but an automated system can run cool air through the bin when it is available to cool the grain to the desired temperature and maintain moisture content.

 

Insect Control

Insect infestations can arise from residue in combines, handling equipment, and old grain left in storage. In addition to all the other management precautions, the grain should be observed for signs of insect activity. Some preventive measures that may help include:

 

Safety

The dangers of grain handling cannot be stressed heavily enough. NEVER enter a bin when the grain is flowing and be extremely cautious around all grain handling structures and equipment. Be sure to have safety precautions and emergency plans in place and make them known to all workers and bystanders on the farm.

Article Link

Sources:
McKenzie, B. and Van Fossen, L. 1995, Managing dry grain in storage. Midwest Plan Service. AED-20. Purdue University. https://www.extension.purdue.edu/extmedia/aed/aed-20.html
Dorn, T. 2010. Ensure quality grain storage by starting with clean equipment, bins. The University of Nebraska-Lincoln. https://cropwatch.unl.edu/ensure-quality-grain-storage-starting-clean-equipment-bins
Additional sources used:
Cloud, H. and Morey, R. 1991. Managing stored grain with aeration. The University of Minnesota Extension. https://extension.umn.edu/corn-harvest/managing-stored-grain-aeration
Hurburgh, Jr., C.R. 2005. Grain quality and grain handling issues in drought areas. Iowa State University Extension. Integrated Crop Management. IC-494(23): 184-186.
https://www.extension.iastate.edu/pages/eccrops/transfer/hurburghrobertson.pdf
Hurburgh, C. 2008. Soybean drying and storage. Iowa State University Extension. Pm-1636.
https://dr.lib.iastate.edu/entities/publication/753b5d08-4db4-41a7-a959-cbb3e58339be
Beck, R., Bauder, S., Edwards, L., Edwards, N., Bly, A., Karki, D. and Davis, J. 2018. Grain storage: It starts with harvest. South Dakota State University. https://www.farmprogress.com/harvest/grain-storage-it-starts-with-harvest
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1018_156794.

Harvesting Lodged and Down Corn

Stalk lodging and down corn can complicate harvest and lead to yield loss and storage issues. Effective harvest management can help minimize yield and storage losses in lodged and down corn.

 

What to Watch For

As corn nears maturity, stalk integrity can be reduced. Stalk strength is naturally reduced by cannibalization, which occurs when nutrients are moved from the stalk to kernels during grain fill. Additionally, stalk rots and secondary pathogens can diminish stalk quality. High winds can cause corn with weakened stalks to lodge, especially in fields where significant cannibalization and stalk rot infection has occurred.

 

Potential Impact of Lodged Corn on Yield and Quality

Fields with considerable lodging can be a challenge to harvest efficiently. Harvest loss is unavoidable even in standing corn. Losses of 1% can occur at the corn head even with the most experienced operators. Most harvest loss in lodged corn occurs because the ears on down corn are not picked up by the corn head and do not make it into the combine. Harvest losses in down corn may be 10 to 15% even when care is taken during harvesting. For each ¾-lb ear left in an area equal to 1/100 of an acre there would be an approximate loss of one bushel/acre. An example of 1/100 of an acre would be equivalent to an operator using an eight-row, 30-inch corn head (20 ft wide) by 21 feet 9 inches long (435.6 sq ft). Lodged corn is also at greater risk of poor dry-down and will be more likely to have molds or kernel sprouting if ears are in contact with the soil. The combination of variable grain moisture, possible kernel molds, and kernel sprouting can increase the challenges of successfully storing the grain.

 

Scout Fields to Determine Lodging Potential 

Start by inspecting fields to identify where corn is down and where it is standing. Check fields for stalk strength using the grab test. Grab the corn stalks at shoulder height, pull or push about 18 inches off center and release. If the corn stalks remain upright, stalk strength is good. If not, stalk strength is weaker. Also determine the grain moisture in the fields. Knowing the percent of corn that is down or lodged as well as the grain moisture can help determine harvest order. Take into consideration that upright corn, depending on stalk strength, is also at risk of lodging. Fields with a high percentage of lodged corn can take three to four times longer to harvest than fields with stalks that are standing well. Therefore, it can be challenging to decide when to harvest the downed corn and the standing corn.

 

Tips to Manage

Fields with considerable lodging can reduce harvest efficiency. Harvesting as many of the down ears as possible requires slower speeds and patience. There are several management tips to help increase the number of ears harvested by the combine:

 

Keep Safety Top of Mind

Harvesting down corn will not be business as usual as it requires much more time and patience than normal corn harvesting operations. Plugging of the corn head is more likely to occur in down corn than standing corn, so keep safety in mind when needing to stop the combine to un-plug the header. Be sure to disengage the corn head before attempting to clear out a plugged row(s).

Article Link

Sources:
McNeill, S., Montross, M. and Stombaugh, T. A comprehensive guide to corn management in Kentucky, Chapter 11. Corn harvesting, drying and storage. University of Kentucky College of Agriculture, Food and Environment. http://www2. ca.uky.edu/agcomm/pubs/id/id139/id139.pdf
Hanna, M. Harvesting lodged corn. Iowa State University Extension and Outreach. https://crops. extension.iastate.edu/encyclopedia/harvesting-lodged-corn
Thomison, P. 2016. Tips for harvesting lodged corn. The Ohio State University Extension. https://agcrops. osu.edu/newsletter/corn-newsletter/2016-33/tips-harvesting-lodged-corn
Legal Statements
Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. ©2023 Bayer Group. All rights reserved.1222_137754.

Can Tillage Help with Corn Insect Management?

 

Can the tillage practice affect insect pressure?

Yes, tillage practices can affect insect pressure. Since the 1970s, acreage has continued to shift from conventional tillage to conservation tillage to help reduce erosion and increase water retention. Conservation tillage has many benefits, but the increased crop residue (Figure 1) can harbor insects. Reduced tillage can result in unincorporated corn residue and weeds in the field. These higher moisture, cooler temperature conditions with full soil cover can provide a habitable environment for slugs and white grubs. Grassy weeds left uncontrolled can attract black cutworm moths and grasshoppers. However, chemical control options can be implemented for weed management.

Wireworm and corn seed maggot populations were thought to thrive under no-till conditions, but newer studies are finding that tillage does not necessarily lower populations of these species. Adult seedcorn maggot flies prefer to lay eggs in partially incorporated corn residue. No-till corn fields may therefore be passed over as an egg-laying site, reducing seedcorn maggot populations. Though due to the fact that soil, residue, and insect interactions are unique to geography and weather, it becomes difficult to rule out residue retention as a contributing cause to increased insect pressure.

 


Figure 1. Remaining corn residue on a strip-tilled field.

 

Is it necessary to switch fields with conservation tillage to conventional tillage?

No, it is not necessary to switch conservation tillage fields to conventional tillage fields. There are many ways to help reduce insect damage. Weed management, crop rotation, planting and harvest timing, and trait selection can help lower insect pest pressure without switching tillage practice. For some insects, reduced tillage can help reduce insect populations.

 

Does residue from traited corn products affect insect populations?

Traits in live plant tissue protect plants from insects during the growing season. However, dead crop tissue – residue – has not been shown to carry the same insecticidal properties over winter. Bacillus thuringiensis (B.t.) proteins are decomposed and dissipated from plant residue, though the rate at which this occurs is influenced by the specific protein from the trait, soil clay content, and precipitation. Research has shown CryIA(b) and Cry3Bb1 proteins had near complete dissipation or decomposition after 41 days and 3.5 months, respectively.

 

Does reduced tillage benefit predatory insect species?

Yes. Natural insect enemies are generalists, switching prey and host species. This generalist activity is favored by providing the habitat and alternate prey of no-till fields. Below are some examples of insect predation from these ‘beneficials’.

 

What modified tillage practices could be used on a field at elevated risk for insect damage?

When tillage is needed to incorporate fertilizer or cover crops, wait two weeks before planting.6 This wait period will expose insects to the elements and bird predation. Insects and slugs needing residue cover can be exposed by clearing any residue on top of rows. Strip-till, or row cleaners, help warm soils to encourage faster germination and reduce insect feeding on seeds.

 

Are there other pests that may be impacted by tillage system?

Yes, two additional major pests are slugs and millipedes. Slugs are common in no-till and conservation tillage systems, particularly after a mild winter that allows the immatures to survive along with the usual overwintering stage, eggs. Millipedes, while not insects, can behave in a similar manner. Millipedes feed on decaying plant matter, organic matter in the soil, and other, smaller soil-dwelling invertebrates. However, they can occasionally feed on corn seedlings. Millipede injury more often occurs under no-till conditions and in wet springs. This is particularly true if seeds are exposed where furrows did not completely close during planting. Seed treatments are not effective against millipedes.

 

Article Link

 

Sources:
Van Wychen Bennett, K., Burkness, E.C., and Hutchison, W.D. 2023. Seed corn maggot. University of Minnesota. VegEdge. https://vegedge.umn.edu/insect-pest-profiles/seed-corn-maggot
Morales-Rodriguez, A., Wichman, D., and Wanner, K.W. 2022. Effects of tillage and fallow rotation
on wireworm populations and damage to cereal grain crops in Montana. Crop, Forage, and Turfgrass Management. Vol. 8 (2): e20193. https://doi.org/10.1002/cft2.20193
Sims, S.R. and Holden, L.R. 1996. Insect bioassay for determining soil degradation of Bacillus thuringiensis subsp. kurstaki CryIA(b) protein in corn tissue. Environmental Entomology. Vol. 25 (3): 659-664. https://doi.org/10.1093/ee/25.3.659
Xue, K., Diaz, B.R., and Thies, J.E. 2014. Stability of Cry3Bb1 protein in soils and its degradation in transgenic corn residues. Soil Biology and Biochemistry. Vol. 76: 119-126. https://doi.org/10.1016/j.soilbio.2014.04.031
Reay-Jones, F.P.F, Chong, J.H., and Ruberson, J.R. 2020. Insect pest management. In, (Bergtold, J. and Sailus, M. eds.) Conservation Tillage Systems in the Southeast. Ch. 13. https://www.sare.org/wp-content/uploads/Conservation-Tillage-Systems-in-the-Southeast_compressed.pdf
Brown, C., Follings, J., Moran, M., and Rosser, B. (Eds.) 2022. Insects and pests of field crops. In, Agronomy Guide for Field Crops. Ontario Ministry of Agriculture, Food, and Rural Affairs. Pub 811. Ch. 15. https://www.ontario.ca/files/2022-10/omafra-agronomy-guide-for-field-crops-chapter-15-en-2022-10-13.pdf
Corn tillage systems. 2014. University of Wisconsin Cooperative Extension. http://corn.agronomy.wisc.edu/Management/L007.aspx.
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1215_178896.

Tillage Effects on Weed Management

Since the beginning of agriculture, tillage in some fashion has been used to prepare a seedbed and manage weeds that use nutrients and water. Tillage can be used in the spring, in-season (rotary hoe, cultivation), and after harvest as a single tactic weed management tool or in combination with other control tactics such as herbicides, cover crops, and flame. The weeds in any given field help determine which tillage system, if any, should be used. Therefore, the weed species in a conventional tillage system can be very different than those in a no-till system.1 The biology and growth habits of annual, biennial, and perennial weeds can greatly affect the type of tillage and tillage equipment necessary for managing weeds. Weeds are propagated by seeds, rhizomes, runners, and tubers; therefore, different control tactics are required for successful management.

 


Figure 1. Moldboard plow at Bayer Learning Center, Gothenburg, NE. Where appropriate, moldboard plowing can bury weed seed below germination levels.

 

Tillage prior to planting

Controlling weeds with tillage prior to planting is a major method to reduce weed density and is often referred to as primary tillage. However, weed control can vary greatly depending on the tillage implement (Table 1). Annual weed control can be greatly enhanced if primary tillage is used in combination with delayed planting, which allows the annual species to germinate prior to the tillage operation. When considering using tillage as a primary weed control method consider the tradeoffs between the yield of a later planted crop against the need for tillage as a weed control tactic. If tillage is delayed until weeds become larger, the effectiveness of tillage can be reduced. Summer annual weeds that are not killed by tillage can be more difficult to control with herbicides later in the season. Additionally, weeds that are injured by tillage and not killed can be harder to kill with herbicides because of their injured vascular tissue limiting the spread of the herbicide through the weed. Some examples of primary tillage implements are the moldboard plow and chisel plow, with the moldboard plow being more effective in burying weeds and weed seeds (Figure 1).

 

Table 1. Weed Control Rating for Various Tillage Implements*
Implement Seedlings Established Annuals or Biennials Sample Perennials Creeping Perennials Burying Annual Weed Seed
Moldboard Plow Good Good Good Fair Good
Chisel Plow Good Fair Fair Poor Fair
Disk Harrow Good Good Good Poor Poor
Field Cultivator Good Poor Poor Poor Poor
*Adapted from A practical guide for integrated weed management in Mid-Atlantic grain crops.3

 

Secondary tillage is not as disruptive as primary tillage and is mainly used to prepare the seedbed. Secondary tillage controls small seedlings and germinating annual weeds by desiccation; therefore, it is best used when soil conditions are dry and temperatures are high.

The stale seedbed system employs an early tillage operation to stimulate weed seed germination (usually 30 days prior to planting). This is followed by a secondary, usually light, tillage operation to destroy the emerging seedlings prior to planting. The use of the stale seedbed system can help deplete weed seed banks, but control of the weeds that germinate should be as complete as possible to prevent replenishing the bank.

 

Table 2. Percent comparison of Amaranthus species seed emergence from various depths by tillage method in 2014*
0 to 1.9 inches (0 to 5 cm) 1.9 to 5.9 inches (5 to 15 cm) 5.9 to 9.8 inches (15 to 25 cm)
Tillage Type Percent of Total Seed Emerged
No-till 71 to 81 17 to 25 0 to 9
Minimum Tillage 77 to 100 0 to 20 0 to 8
Conventional Tillage 71 to 77 22 to 29 0 to 5
Deep Tillage 20 to 25 63 to 80 0 to 13
*Dr. Kevin Bradley, University of Missouri. Influence of Tillage Methods on Management of Amaranthus Species in Soybean.4 Data from one site each in Arkansas, Illinois, Indiana, Ohio, Tennessee, and Wisconsin and two sites in Missouri. Data used with the permission of Dr. Bradley.

 

In addition to reducing growing weeds, primary and secondary tillage can change the distribution of weed seed in the soil profile, which can influence germination and seedling establishment. In some cases, seed can get buried by tillage to a depth that retards germination (moldboard plow) and in others, tillage brings seed to the surface, providing an environment suitable for germination. In a multi-state university study, the percent of germinating Amaranthus species seed from a depth of 5.9 to 9.8 inches (15 to 25 cm) was dramatically reduced compared to depths of 0 to 5.9 inches (0 to 15 cm) (Table 2). The optimum emergence depth for different weeds can vary (Table 3). Should a field, particularly a no-till field, develop high populations of herbicide resistant weeds that become unmanageable with chemistry, cover crops, or other methods, a one-time deep moldboard plowing might be a consideration to help return the field to a manageable weed level (Tables 3).

 

Table 3. Average optimum emergence depth for six common weed species*
Weed Species Emergence Depth (inches)
Broadleaf signalgrass 0 to 3/8
Common ragweed 0 to 1 9/16
Horseweed (marestail) 0 to 3/16
Palmer amaranth 0 to 1/2
Pitted morningglory 1 9/16
Slender amaranth 3/16 to 13/16
*Adapted from A practical guide for integrated weed management in Mid-Atlantic grain crops.3

 

Generally, perennial weeds and small-seeded weeds (i.e., lambsquarter) are more common in no-till systems as the roots of the perennials are undisturbed and small-seeded weed seeds are not buried below the germination depth. On the other hand, some large-seeded weeds such as pitted morningglory may be unable to become established when seeds are left on the soil surface.

 

Tillage after planting

There are two tillage types used for managing weeds after planting: blind cultivation and inter-row cultivation. Blind cultivation is done without regard to the crop rows and is usually used to dislodge small weeds; the most common implement used for blind cultivation is a rotary hoe (Figure 2). Plant size dictates the time limit on the use of blind cultivation. While corn and soybean are good candidates for blind cultivation, small-seeded crops are not as they can become easily dislodged. Timing is critical for blind cultivation to be successful; the “white thread”
stage (seed has germinated but not emerged) of weed seed germination is associated with the most consistent control.

Inter-row cultivation has become more precise and can be done with more speed with the advent of guidance support systems. While they were originally designed for low residue systems, equipment modifications now allow for use in higher residue systems. Usually there is more time to use inter-row cultivation with row crops as compared to using blind cultivation.

In summary, tillage can be used as a single tactic to manage weeds; however, it is important to know the weed species present in a field along with their growth habits for best tillage management. Primary, secondary, and blind tillage use different implements to kill weeds, dislodge weeds from the soil, or bury weed seeds. Consideration should be given to the use of tillage in conjunction with other cultural and chemical tactics to provide a more consistent and sustainable weed management program.

 


Figure 2. A rotary hoe can dislodge small weeds in a growing crop.

Article Link

Sources
Buhler, D. 1995. Influence of tillage systems on weed population dynamics and management in corn and soybean in the central USA. Crop Science 35(5):1247-1258. https://doi.org/10.2135/cropsci1995.0011183X003500050001x
Hager, A. 2013. Control weeds before planting. University of Illinois Extension. farmdoc. https://farmdoc.illinois.edu/field-crop-production/weeds/control-weeds-before-planting.html
Cahoon, C., Curran, W. and Sandy, D. 2019. A practical guide for integrated weed management in Mid-Atlantic grain crops. VanGessel, M. (ed.) Pennsylvania State University, University of Delaware, Virginia Tech, and West Virginia University.
https://growiwm.b-cdn.net/wp-content/uploads/2019/10/IWMguide.pdf?x75253&x71059
Farmer, J.A., Bradley, K.W., Young, B.G., Steckel, L.E., Johnson, W.G., Norsworthy, J.K., Davis, V.M., and Loux, M.M. 2017. Influence of tillage method on management of Amaranthus species in soybean. Weed Technology, 31, 10-20. https://doi.org/10.1614/WT-D-16-00061.1
Additional source:
Mohler, C.L., Teasdale, J.R., and DiTommaso, A. 2021. Chapter 4. Mechanical and other physical weed management. Manage Weeds on Your Farm. Sustainable Agriculture Research and Education (SARE). National Institute of Food and Agriculture (NIFA) and United States Department of Agriculture (USDA).
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1223_54011

How Can Harvest Help Determine Future Insect Pressure in Corn?

While harvesting corn, combine operators should know how to recognize certain insect feeding injuries. Though the insect may no longer be present, injury symptoms may well be noticeable. If symptoms are present, proactive insect management— including scouting—should be considered for the next crop year.

 

Missing plants or skips within row

Early season injury from white grubs or wireworms could cause missing plants or skips within a row. As these insects usually occur in the same fields over time, management tactics should be considered in the next growing season.

 

Random ears are banana shaped or have random discolored kernels

Brown, green, or brown marmorated stink bug feeding is a likely cause of these symptoms (Figure 1). Heavy stink bug pressure early in the season can lead to deformed, banana-shaped ears (Figure 2). Random kernels may have scars, holes in kernel caps, or appear bruised and dark (Figure 3). Kernels may be mottled in appearance, especially close to the tip of the ear. The following crop should be closely scouted for stink bug damage and managed accordingly, especially if the field has a history of damage.

 


Figure 1. Brown stink bug.

 


Figure 2. Banana shaped ears are characteristic of stink bug feeding.

 


Figure 3. Random discolored kernels occur when stink bugs pierce through the husk to feed on developing kernels.

 

Kernels are damaged by larval feeding and/or have fungal growth

Mid- to late-season kernel feeding from corn earworm (Figure 4), fall armyworm, western bean cutworm (Figure 5), and European corn borer (Figure 6) can directly damage corn kernels by feeding on them, and indirectly lead to increased incidence of disease and rot. When kernel feeding begins during the milk stage of kernel development, the leaking milk provides a favorable substrate for fungal growth which can then damage neighboring healthy kernels (Figure 4). Above-ground Bacillus thuringiensis-protected (B.t.-protected) corn products may resist some or all of these insect larvae. However, large moth flights of corn earworm can indirectly damage B.t.-protected corn. These moths may produce unusually high numbers of larvae, potentially leading to cannibalism among the larvae which further allow the surviving larvae to grow to a large enough size to tolerate the B.t. toxin, resulting in subsequent damage.

 


Figure 4. Combined kernel damage from corn earworm feeding and fungal growth on non- B.t.-protected corn.

 


Figure 5. Western bean cutworm larvae.

 


Figure 6. European corn borer larvae.

 

Evidence of incomplete pollination

During pollination, insect feeding on green silks can prevent ovule (potential kernel) fertilization if the pollen tube, which is attached to an ovule, is cut. This can occur when silks are clipped to less than ½-inch long. Although the silk-clipping insects are no longer a threat to a crop being harvested, scouting for grasshoppers, corn rootworm beetles, corn earworm, and Japanese beetles should be conducted the following year (Figures 7 and 8).

 


Figure 7. Western corn rootworm beetles feeding on silks.

 


Figure 8. Japanese beetles clipping silks.

 

Stalk or root lodging

Stalk- and/or root-lodged corn can cause substantial harvest delays and losses. European corn borer (ECB), southwestern corn borer (SCB), and common stalk borer feeding can weaken stalks and increase the potential for lodging via wind and heavy rain. Holes in the stalk rind and ear shanks are evidence of European corn borer feeding (Figure 9, left). Dropped ears with tunneled-out shanks, broken tassels, or missing tassels can also be evidence of ECB feeding.

Stalks cleanly broken off just above the brace roots are characteristic of southwestern corn borer feeding (Figure 9, right). SCB tunnel downward into the brace roots and generally stay low on the stalk.

 


Figure 9. European corn borer with entry hole below the ear (left) and southwestern corn borer with tunnel within brace roots (right).

 

Common stalk borer tunneling usually occurs early season along fence rows, waterways, and other grassy areas (Figure 10). Injured plants can be stunted and have characteristic tillering because the growing point was killed or damaged.

Severe root lodging or goosenecked plants are characteristic of mid-season rootworm feeding. Depending on the growing season, injured roots may have new growth. However, this new growth is unlikely to support the plant in severe wind or heavy rain.

Stalk and root lodging is also caused by pathogens, which can be introduced by ECB, SCB, or corn rootworm feeding. Selecting corn products with B.t. protection for above-ground insects, below-ground insects, or both can help protect the plants from respective insect feeding.

 


Figure 10. Common stalk borer. Picture courtesy of and used with the permission of James Kalisch, University of Nebraska, Bugwood.org.

 


Figure 11. Root lodging can be caused by mid-season corn rootworm feeding.

 

Moldy corn

Corn contaminated by aflatoxin has been infected by either Aspergillus flavus or Aspergillus parasiticus. These molds often occur when insects feed on corn ears during droughty, high-temperature conditions. A felt-like, greenish-yellow to yellowish-brown mold can be found near insect damage on or between kernels (Figure 12). Sampling for Aspergillus can be done during grain loading by passing a cup multiple times within a stream of grain. Multiple samples should be taken, as distribution is not even within the field. Rapid tests are available for in-field testing. It is important to know that Aspergillus may be present without the development of aflatoxin.

 


Figure 12. Ear with insect larval feeding and Aspergillus fungus that may be aflatoxin.

 

Ragged-edged corn leaves or leaves with ragged holes

Leaves with ragged edges or ragged holes (Figure 13) may be evidence of fall armyworm (FAW) feeding pre-tassel. Grasshopper feeding can mimic FAW feeding and is more likely to be seen during harvest than FAW.

 


Figure 13. Ragged leaves and holes caused by fall armyworm.

 

Article Link

 

Sources:
12019. Stink bug kernel injury. The Ohio State University. Troubleshooting Abnormal Corn Ears. https://u.osu.edu/mastercorn/stink-bug-kernel-injury/
Wrather, A., Sweets, L., Bailey, W., Claxton, T., Sexten, J., and Carlson, M. 2010. Aflatoxins in corn. University of Missouri Extension. G 4155.
https://extension2.missouri.edu/g4155
Nielsen, B. and Colville, D. 1988. Stalk lodging in corn: Guidelines for preventive management. Agronomy Guide. Purdue University. AY-262. https://www.extension.purdue.edu/extmedia/AY/AY-262.html.
O’Day, M., Becker, A., Keaster, A., Kabrick, L., and Steffey, K. 1998. Corn insect pests – A diagnostic guide. University of Missouri Extension. https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/16081/CornInsectPests. pdf?sequence=1&isAllowed=y.
Dean, A. and Hodgson, E. Stalk borer. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/encyclopedia/stalk-borer.
Bessin, R. 2019. Fall armyworm in corn. University of Kentucky College of Agriculture, Food and Environment, Lexington, KY. Entfact-110.
https://entomology.ca.uky.edu/files/efpdf1/ef110.pdf
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1215_178659

Performing a Corn Stalk Nitrate Test

Q. What is the corn stalk nitrate test?

The corn stalk nitrate test (CSNT) is conducted late in the season and can be a reliable end-of-season indicator of crop nitrogen (N) status. The test reflects N availability during the growing season and provides a tool to help growers determine if their N management practices were adequate. The CSNT provides an assessment of whether the crop had the right amount of N, too much N, or was N limited.

 

Q. When should you collect samples for the CSNT?

Sampling can be done anytime between ¼ milk line up to about 3 weeks after black layer formation, before grain harvest. If used for silage corn, sample at the time of harvest or within 24 hours after harvest, as long as there is no rainfall between the time of harvest and sampling. The stubble height needs to be at 14-inch (35.5 cm) for an accurate test.

 

Q. How should CSNT samples be taken?

 

Q. How do you prepare the samples and what should you do with them?

 

Q. What will the lab results tell you?

The CSNT is based on the concentration of nitrate-N in the lower corn stalk when the plant is near or at maturity. Lab results will indicate the following:

 

Table 1. Interpreting a corn stalk nitrate test result.
Nitrate Concentration Nitrate Level Interpretation
<250 ppm Low
250 – 700 Marginal
700-2000 ppm Optimal
>2000 ppm Excessive
Modified from Kaiser, D. and Fernandez, F. 2020. How to take and interpret the basal stalk nitrate test. University of Minnesota. https://blog-crop-news.extension. umn.edu/2020/09/how-to-take-and-interpret-basal-stalk.html.

 

Q. What are the limitations of the CSNT?

The CSNT can be greatly influenced by weather, soil productivity, and management practices. The following factors can complicate interpretation of the test results:

The test does not provide an indication of the amount of N that was over- or undersupplied. Test result readings of high concentrations (>2000 ppm nitrate) are more definitive and provide greater confidence that there is excess N available to the plant. Less confidence can be placed on low nitrate level interpretations or in specific N-rate adjustments.

 

Q. What can you learn and how can you use information from the CSNT?

The CSNT can be used as a long-term approach to evaluate your N management and to help guide future N applications toward economically optimal rates. The test will tell how you did, not what you need to do. The test will not tell you what management practices to change but instead provides information about how your N management is performing. Decisions can be made to adjust the fertility program for subsequent years based on the results of the CSNT.

CSNT results are most useful when evaluated over a period of several years on the same field. Basing future N rate decisions solely on one year’s CSNT values could result in poor management decisions. CSNT data collected over several years coupled with fertilizer and manure application history, growing season weather conditions, soil type and productivity, and general crop management history information can be used to determine if N fertilizer rates should be reduced to improve profitability.

The test is best suited to understanding when N applications are greater than the crop need. If the CSNT shows high nitrate levels for several seasons, then it becomes evident that N applications are too high and should be adjusted to more moderate rates. Continued monitoring of CSNT results will show if stalk nitrate levels decrease into the optimal range after adjusting N-application rates. Using the CSNT can result in greater N use efficiency and thus profitability, and helps to reduce the potential for negative environmental impacts from N that is not being utilized by the crop.

Article Link

Sources
Kaiser, D. and Fernandez, F. 2020. How to take and interpret the basal stalk nitrate test. University of Minnesota. https://blog-crop-news.extension.umn. edu/2020/09/how-to-take-and-interpret-basal-stalk. html
Laboski, C. 2016. Considerations when using the end-of-season corn stalk nitrate test. University of Wisconsin Integrated Pest and Crop Management. https://ipcm.wisc.edu/blog/2016/09/considerations-when-using-the-end-of-season-corn-stalk-nitrate-test/
Milander, J., Iqbal, J., Mamo, M., and Timmerman, A. 2022.-Using a Cornstalk Nitrate Test to Evaluate Nitrogen Management Decisions. University of Nebraska. https://cropwatch.unl.edu/2022/using-cornstalk-nitrate-test-evaluate-nitrogen-management-decisions
Zebarth, B.J., Drury, C.F., Tremblay, N., and Cambouris, A.N. 2009. Opportunities for improved fertilizer nitrogen management in production of arable crops in eastern Canada: A review. Canadian Journal of Soil Science. 89: 113-132. https://doi.org/10.4141/CJSS07102
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1213_134529

Fall Residue Retention or Tillage for Disease Management

Considerations for Residue Management

Crop residue retention improves the biological, physical, and chemical properties of soil. Additionally, nutrient recycling is a reason to conserve residue through no-till or minimal-tillage field management. Conservation tillage increases these benefits, though it also increases the inoculum sources for certain corn diseases. Crop residue has long been known as an inoculum source to spread disease.

Epidemics of soil-borne diseases tend to occur when susceptible crops are grown for several consecutive years. Crop residues and soil contain pathogens that can remain in their dormant state until conditions favor the development of the disease cycle. The primary infection source of soil-borne disease is the population of pathogens, also known as the inoculum, in the area. This is in contrast to air-borne diseases, such as common and southern rust, which initiate infection when their inocula are blown into an area on air currents.

 


Figure 1. Baled corn residue reduces disease inoculum.

 

Surface Residue Management

Corn residue remaining on the soil surface has been reported to potentially result in earlier and more severe infections of fungal diseases such as northern corn leaf blight or southern leaf blight. Where these diseases have been a problem, crop residue can be buried with tillage, baled (Figure 1), or grazed in the fall to reduce the amount of residue on the soil surface post-harvest. By reducing the initial plant disease inoculum, the risk of early onset of the disease can be lessened. Early onset infections may cause more yield loss compared to infections that begin in the later stages of grain fill. Growers should also consider controlling weeds growing in tree lines or fence lines that could serve as alternate hosts for diseases. For example, green foxtail can be a host for northern corn leaf blight and pigweed species can be a host for Fusarium species.

 

Some Tillage Leaves Some Residue – Disease Dependent Tillage Recommendations

Tillage can help lower the survival of most common fungal pathogens by mixing plant residue into the soil. Soil contact increases the rate at which plant residue is decomposed by non-pathogenic soil microorganisms, which feed on the residues and outcompete many pathogenic inocula that might otherwise survive if the residue remained on the soil surface. For example, the fungus which causes anthracnose leaf blight, top die-back, and stalk rot, Colletotrichum graminicola, is a poor competitor with soil microorganisms. Research has shown that populations of C. graminicola are reduced to undetectable levels after three months of being buried but can remain aggressively infectious for 10 months if left on the surface.

Minimum and conventional tillage can reduce the inoculum of Gibberella zeae, the organism that causes Gibberella stalk rot and ear rot. However, even small amounts of corn residue can affect the spread of this particular disease. A study evaluated the effect of three tillage types—ridge-tillage, mulch-tillage, and no-tillage—on the disease severity of northern corn leaf blight and yield levels in three corn products. The ridge-tillage treatment involved planting on a tillage ridge from the previous crop and the mulch-tillage treatment involved fall and spring cultivation with no moldboard plow. After two years of northern corn leaf blight infection in the test fields, the researchers found higher yields and lower disease levels in the ridge- and mulch-tillage plots compared to the no-tillage plots, though certain products had more resilience to the disease. Although ridge-tillage left residue on the soil surface over winter, the use of row cleaning attachments on the planter which moved material to the side of the seed furrow (Figure 2) was believed to reduce initial inoculum and early onset of plant infections.

 


Figure 2. Moving residue away from the seed furrow can reduce the amount of inoculum present that may result in the early onset of plant infections.

 

Gray leaf spot (Cercospora zeae-maydis) cannot successfully survive when infected residue is buried. Generally, if residue covers 30 percent or more of a field that had gray leaf spot the previous season, there is the potential for damaging levels of the disease if favorable weather conditions occur. However, as little as 10 percent residue coverage can lead to considerable infection and subsequent yield loss if the corn product being planted has low tolerance to gray leaf spot. Although crop rotation can help reduce gray leaf spot inoculum levels, infected leaf and stalk/husk debris can remain after one or two years, respectively, particularly in minimum-tillage systems. A study documented that the severity of gray leaf spot increased as minimum tillage (greater than 15% surface residue) adoption increased through the 1980’s and 1990’s. Thus, where reduced tillage is implemented, tolerant corn product selection and fungicide use, when necessary, are essential tools to combat this pathogen.

 


Figure 3. Corn residue management is a cultural practice to manage some foliar diseases.

 

Summary

Tillage is a way to reduce disease inoculum and decrease the risk for some corn diseases such as gray leaf spot, northern corn leaf blight, and southern corn leaf blight and stalk rots. Small amounts of disease inoculum in combination with favorable conditions for disease development can increase disease pressure even for well-managed crops. Therefore, an integrated management approach should be used to control these diseases.

Other key factors in corn disease pressure have been noted by researchers, including weather, corn product resistance, crop rotation, and location. Consider the disease history of the field before tilling this fall and when placing corn seed orders.

 

Article Link

 

Sources
Pedersen, W.L. and Oldham, M.G. 1992. Effect of three tillage practices on development of northern corn leaf blight (Exserohilum turcicum) under continuous corn. Plant Disease vol. 76: 1161-1164. https://www.apsnet.org/publications/plantdisease/backissues/Documents/1992Articles/PlantDisease76n11_1161.PDF
Jirak-Peterson, J.C. and Esker, P.D. 2011. Tillage, crop rotation, and hybrid effects on residue and corn anthracnose occurrence in Wisconsin. Plant Disease vol. 95: 601-610. https://doi.org/10.1094/PDIS-11-10-0837
Keller, M.D., Thomason, W.E., and Schmale, D.G. III. 2001. The spread of a release clone of Gibberella zeae from different amounts of infested corn residue. Plant Disease vol. 95: 1458-1464. https://doi.org/10.1094/PDIS-03-11-0218
Mohler, C. L. and Johnson, S. E. 2009. Crop rotation on organic farms, a planning manual. Sustainable Agriculture Research and Education (SARE). https://www.sare.org/wp-content/uploads/Crop-Rotation-on-Organic-Farms.pdf
Rees, J. and Jackson-Zeims, T. 2008. Gray leaf spot of corn. NebGuide G1902. University of Nebraska-Lincoln. https://extensionpublications.unl.edu/assets/html/g1902/build/g1902.htm
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. ©2023 Bayer Group. All rights reserved. 1211_177102.

Managing Stored Grain during Fluctuating Temperatures in the late Fall and Winter

Managing grain quality during late fall and winter is an ongoing chore that can be even more challenging when temperatures fluctuate on a daily basis. To avoid grain quality loss, growers should be aware of what changing temperatures can possibly do to stored grain and what important steps that can be taken to manage grain temperatures.

 

Why changes in temperature can cause storage problems for grain.

Inconsistent air temperatures can occur frequently across much of the grain producing areas of the United States and Canada in late fall and throughout the winter. Checking the condition of stored grain during this period is crucial to maintaining the quality and value of the product. Crusted, wet, or sticky kernels can be signs of trouble inside the grain bin.

Solar radiation in the winter can cause issues when it comes to grain temperature. The amount of solar energy on the south side of a bin in February is much greater than in June. Grain within two feet of the bin walls may be warmer than the average air temperature (Figure 2).

 


Figure 1. Grain bin in winter.

 


Figure 2. Illustrating the effects of potential temperature swings throughout a given day during the fall and winter months.

 

The most important cause of deterioration of dry stored grain is grain temperature. If temperature is not controlled, moisture can migrate from one part of the grain mass to another, where it can accumulate and potentially cause spoilage.

What causes air and moisture to migrate within a grain bin? It is estimated that the air space within a grain mass can range from about 30% to 60% of the total space. The temperature of the air surrounding the grain is about the same temperature as the grain. As average daily temperatures outside of the bin decline in late fall/early winter to 20 °F and colder, the walls of the bin also become cooler. Since grain has fairly good insulation properties, most of the center mass of grain (and the air surrounding the grain) remain at about the same temperature as when the grain was placed in storage. These temperature differences create a circulation of air and moisture known as convection currents. The cooler air surrounding the grain near the bin walls becomes denser and settles near the bin floor. It then migrates toward the center of the grain mass where the warmer grain increases the air temperature, causing it to become less dense and rise through the warm grain. As it rises, the air absorbs small amounts of moisture. Then the air continues to make its way into the upper part of the grain mass and the top of the bin, which is cooler. As it cools, condensation can occur, and moisture is deposited in the grain. This can lead to spoilage (moldy grain) and/or crusting, usually in the top center of the grain surface.

 

What is Equilibrium Moisture Content and why is it important?

Equilibrium moisture content (EMC) is the percent moisture content at which grain will stabilize, given a certain temperature and relative humidity (RH) of the air surrounding the kernels. The EMC charts for several types of grain crops can be found at this link: https://extension.okstate.edu/fact-sheets/aeration-management-knowing-when-to-run-aeration-fans. html.

Why is this information so important to grain storage managers? Regardless of how much air fans supply to a bin, the temperature and RH of that air will dictate whether the grain will decrease or increase in moisture content (MC). The stabilization time is impacted by the amount of air supplied. However, the final grain moisture content is determined by the temperature and relative humidity of the air. If a certain MC is desired for the grain being stored, it is important to know whether air being supplied will either deposit moisture in the grain or remove moisture from the grain. If the desired condition of the grain cannot be met given the temperature and RH of the air, then it is not cost efficient to run the fans. For example (Table 1), if corn is being stored in a bin and the outside air conditions are 50 °F and the RH is 70%, the resulting MC of the grain aerated over time will be an EMC of 15.7% (using the EMC chart for corn found in the link above). If the goal is to maintain or reduce the moisture content, do not run fans in conditions that would cause a higher MC as found in the EMC chart. Once a stored crop is close to a safe storage moisture, aeration can be more efficient. If corn inside the bin is at 16% moisture, and you want to dry it to 15%, running the fan in air condition scenarios A, C, E and F (Table 1) would help achieve that goal, as the EMC’s are lower than 15%. Scenarios B and D would not achieve that goal as the EMC’s are above 15%.

 

Table 1. Equilibrium Moisture Content for corn resulting from three different temperature and two different relative humidity levels.
Air condition scenario Air Temperature (°F) Relative Humidity (RH) Equilibrium Moisture Content
A 40 50 12.7
B 40 70 16.4
C 50 50 12.2
D 50 70 15.7
E 70 50 11.2
F 70 70 14.5
Adapted from Aeration management: Knowing when to run aeration fans. Oklahoma State University.4

 

Tips on managing stored grain during temperature fluctuations.

 

Safety

The dangers of grain handling cannot be stressed heavily enough. NEVER enter a bin when the grain is flowing and be extremely cautious around all grain handling structures and equipment. EXTREME CAUTION should be used if entering a bin with moldy grain or if the upper layer of grain is crusted. Be sure to have safety precautions and emergency plans in place and make them known to all workers and bystanders on the farm.

 

Article Link

Sources:
1Mahrenholz, A. 2022. Keeping your grain safe in fluctuating temperatures. Purdue University Extension.
https://extension.purdue.edu/news/county/pike/2022/03/pike-keeping-your-grain-safe-news.html
2McKenzie, B. and Van Fossen, L. 1995. Managing dry grain in storage. Purdue University Extension. AED-20.
https://www.extension.purdue.edu/extmedia/AED/AED-20.html
3Hellevang, K. 2020. Proper spring grain drying and storage critical. North Dakota State University. Extension and Ag Research News.
https://www.ag.ndsu.edu/news/newsreleases/2020/march-23-2020/proper-spring-grain-drying-and-storage-critical
4Jones, C. 2018. Aeration management: Knowing when to run aeration fans. Oklahoma State University Extension. BAE-1116. https://extension.okstate.edu/fact-sheets/aeration-management-knowing-when-to-run-aeration-fans.html
5Dawson, A. 2013. Knowing when it’s time to turn on the aeration fan. Manitoba Co-operator. https://www.manitobacooperator.ca/crops/knowing-when-its-time-to-turn-on-the-aeration-fan/
Additional sources:
Cloud, H.A. and Morey, R.V. 2018. Managing stored grain with aeration. University of Minnesota Extension. https://extension. umn.edu/corn-harvest/managing-stored-grain-aeration
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