Will Spring Tillage Help Me Reduce Disease in My Corn Field?

• Tillage can be one way to help reduce pathogen inoculum in a diseased field.
• The potential for disease development in a corn field is an annual occurrence based on the disease triangle.
• Integrated Pest Management (IPM) approaches should be used to help reduce the potential for corn diseases to develop and intensify.

The potential for disease development in a corn field is an annual occurrence based on the disease triangle. For diseases to develop, there must be (1) a susceptible host (the plant), (2) a pathogen present, and (3) a favorable environment for the disease to develop and intensify. The susceptibility of a corn product to a particular disease is based on its genetic background and relative maturity (RM). Genetically, a corn product may have low, medium, or high tolerance or resistance to a disease. While the RM of a corn product does not directly contribute to a product’s disease tolerance or lack thereof, the RM of the product may be a factor because it may lead to a product being more or less vulnerable to infection at different times when different diseases are more or less prevalent.

Integrated Pest Management (IPM) approaches—which can include scouting, corn product selection, crop rotation, tillage, fungicide applications, seed treatments, planting date selection, insecticide applications, and field drainage improvements—should be used to help reduce the potential for corn diseases to develop and intensify.

The approach used to manage various corn diseases can differ in response to the causal pathogen, which can be fungal, bacterial, viral, or a result of nematodes or oomycetes. Fungal diseases result from the transmission of fungal reproductive spores that inhabit infected residue, bacterial diseases result from bacteria that may be present in or on crop residue, and viral diseases result when inoculum is injected into plants by infected insects and mites.

Tillage can be one way to help reduce pathogen inoculum in a diseased field; however, complete burial of all stalk and leaf residue is necessary to reduce inoculum to near undetectable levels. University of Wisconsin information indicates that remaining surface residue varies by tillage method:¹

• < 10% with moldboard plowing
• 25 to 75% with chisel plowing
• 25 to 75% with disking
• 40 to 60% with ridge-planting and till planting
• > 90% with no-till planting

Anthracnose leaf blight caused by the fungus Colletotrichum graminicola survives on corn residue between seasons but competes poorly with other soil organisms.² A North Carolina study showed that C. graminicola was not detectable after being buried for three months but survived for ten months when left on the soil surface.³

Continuous Corn Systems

Disease inoculum has the potential to increase when susceptible crops are planted in consecutive years. Allowing two to three years between susceptible hosts should give residue adequate weathering to help decrease the viability of disease-causing inoculum.¹ Tillage between each planting could help reduce inoculum, and as indicated in the Wisconsin information, moldboard plowing is the best tillage method for destroying inoculum. However, moldboard plowing opens soils for wind and water erosion, so the method is rarely used today. As such, inoculum is likely to be present annually.

Scouting, historical field information, and the disease triangle should be used to help determine disease management for the following corn crop. For example, if the growing season is dry with little fog, foliar diseases such as gray leaf spot (GLS) may not develop even if inoculum is present from a previous crop because the disease is favored by moist growing conditions.

In a continuous corn growing system, fungicidal and insecticidal seed treatments should be considered to help protect seeds and seedlings from soil pathogens. Selecting corn products with high tolerance or resistance to known, previous diseases should be seriously considered if such products are available. Continuing the previous example, selecting a product that is highly tolerant to GLS protects plants from the disease regardless of the growing conditions.

Product selection is very important when continuous corn fields have a history of ear rots. Even small amounts of infected residue can provide the inoculum to infect not only the previously infected field but also to infect surrounding fields if growing conditions are favorable for spore growth and spread. Gibberella zea is an ear rot fungus known to spread great distances from the inoculum source.⁴ Gibberella stalk rot can be present without the presence of ear rot; however, the infected stalk rot residue can still be the future source for ear rot infection. Additionally, corn products with long, tight husks may be more prone to ear rots, because the husk retains moisture around the ear. Tillage, particularly moldboard plowing, could be beneficial for reducing G. zea inoculum.⁵ Surrounding wheat fields could also be an inoculum source for G. zea, as wheat is another host for the disease.

Reduced Tillage Systems

Though reduced tillage systems help limit erosion and promote soil health, surface residue increases the opportunity for seedling and growing season diseases to occur because of pathogens living on the residue (Figure 1). Cool, wet soils after planting can cause seedlings to be exposed to soilborne pathogens for longer periods and increase the potential for seedling diseases. Fungicidal and insecticidal seed treatments help prevent seedling diseases, and seed products with high tolerance to potential growing season diseases should be considered.

Though the development of many pathogens is favored by moist growing seasons, others—such as charcoal stalk rot—are favored by hot and dry growing conditions. Therefore, seed products should be selected based on historical growing conditions for the area. No-till fields have been reported to have higher levels of GLS compared to fields with any form of reduced tillage.⁶ Surface residue has also been attributed to earlier and more severe infections of northern corn leaf blight (NCLB), southern leaf blight (SLB), and yellow blight (YB).⁶ University of Illinois research studied the effects of (1) ridge-tillage [planting on a tilled ridge from the previous crop], (2) mulch-tillage [fall and spring cultivation, no moldboard plowing], and (3) no-till on NCLB severity.⁶ Greater yields occurred in ridge- and mulch-tillage plots, and were attributed to their lower NCLB levels compared to the no-till plots. Although the ridge-till method in the study left similar amounts of residue on the soil surface over winter as no-till, the use of planter furrow-openers appeared to reduce initial inoculum and early-onset of NCLB infection.⁶

With reduced tillage systems, seed products with enhanced foliar disease packages should especially be considered. Seed products with trait protection for insects such as black cutworm (BCW), European corn borer (ECB), and southwestern corn borer (SWCB) should also be considered. Black cutworm moths can be attracted to early emerging weeds in reduced tillage fields to lay eggs which can produce larvae to feed on seedlings. The larvae of ECB and SWCB can overwinter in residue, becoming adult moths which may then lay eggs in a continuous reduced-tillage field or migrate to other fields and lay eggs.

Additionally, planting equipment should be adjusted to clear residue from the row, which can help warm the soil for quicker seedling growth. Crop rotation to non-host crops is more important in reduced-tillage systems to help reduce the potential for inoculum survival. Routine in-season crop scouting should be conducted to identify economical disease development that foliar fungicides can potentially manage.

Crown Rot and Tillage

Crown rot usually appears later in the growing season on plants that were predisposed to infection during the seedling growth stage. Crown rots are often caused by Fusarium fungi species, with the exact species varying depending on early season growing conditions (Figure 2). One research study demonstrated that fall plowing resulted in increased Fusarium stalk rot compared to no-till.⁷ However, the results were attributed to stress related to a lower soil moisture level in tilled soil compared to higher moisture levels in non-tilled soil. For additional information, please read Crown Rot in Corn.

Soil Compaction with Spring Tillage

Spring tilling fields that are at their field moisture capacity should be avoided, as soil compaction can occur and lead to poor drainage, water infiltration, and poor root growth. Restricted roots can lead to poor water and nutrient uptake, which can then stress seedlings, increase the potential for early season disease development, and predispose plants to late season pathogens such as crown rot. Spring is not the best time to attempt to alleviate deep compaction (deeper than eight inches) with tillage tools, as wet soils can be scarified and compacted by the tillage sweep or shoe. However, cover crops like oilseed radishes have successfully broken through plow pans and compaction layers with their deep roots. Perennial crops such as alfalfa are also good choices to help alleviate compaction and break the disease cycle.⁸

Bacterial Diseases and Tillage

Bacterial corn diseases include Stewart’s bacterial wilt, Goss’s bacterial wilt, Holcus spot, bacterial leaf streak, and bacterial stalk rot. Spring tillage may reduce the amount of bacterial disease inoculum that successfully overwinters on infected residue, reducing the next year’s inoculum. However, exposed residue can still harbor inoculum and be spread by splashing rain, wind, animals, and by infected insects such as corn flea beetles. Infected corn flea beetles are responsible for infecting corn with Stewart’s bacterial wilt, so scouting seedlings to identify corn flea beetle infestations is important for management along with using resistant corn products. Crop injury from hail, wind, or wildlife can help spread or infect plants with bacterial diseases. Additionally, growers should evaluate corn products’ resistance characteristics for bacterial diseases. Even if a disease cannot be managed, knowledge of the infection may help determine harvesting priorities.

Viral Diseases and Tillage

Spring tillage would have little impact on viral corn diseases. These diseases are transmitted by infected insects such as corn leafhoppers (Corn Stunt Disease) and aphids (Maize Dwarf Mosaic Virus). Scouting and knowing the historical presence of infecting insects can be beneficial for managing viral diseases.

Sources

¹2014. Corn tillage systems. University of Wisconsin Extension. http://corn.agronomy.wisc.edu/Management/L007.aspx#Pest%20Control

²Jirak-Peterson, J.C. and Esker, P.D. 2011. Tillage, crop rotation, and hybrid effects on residue and corn anthracnose occurrence in Wisconsin. Plant Disease. 95(5): 601–610. https://doi.org/10.1094/PDIS-11-10-0837

³Naylor, V.D. and Leonard, K.J. 1977. Survival of Colletotrichum graminicola in infected corn stalks in North Carolina. In, Plant disease reporter: Volume 61. Bureau of Plant Industry, U.S. Department of Agriculture.

⁴Keller, M.D., Thomason, W.E., and Schmale, D.G., III. 2011. The spread of a released clone of Gibberella zeae from different amounts of infested corn residue. Plant Disease. 95(11): 1458–1464. https://doi.org/10.1094/PDIS-03-11-0218

⁵Woloshuk, C. and Wise, K. 2010. Gibberella ear rot. Purdue Extension, Diseases of Corn. BP-77-W. https://www.extension.purdue.edu/extmedia/BP/BP-77-W.pdf

⁶Pedersen, 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. 76(11): 1161–1164. https://doi.org/10.1094/PD-76-1161

⁷Lipps, P.E. and Deep, I.W. 1991. Influence of tillage and crop rotation on yield, stalk rot, and recovery of Fusarium and Trichoderma spp. from corn. Plant Disease. 75(8): 828–833. https://doi.org/10.1094/PD-75-0828

⁸Wortmann, C.S. and Jasa, P.J. 2009. Management to minimize and reduce soil compaction. University of Nebraska–Lincoln Extension. G896. https://extensionpublications.unl.edu/assets/html/g896/build/g896.htm.

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