Key Points

• Continuous corn production presents several challenges; however, proper management and realistic goals can help realize yield potential for a continuous corn system.
• Pest management in a continuous corn system may require different and more intense management strategies than rotated acres.
• Corn products with higher disease resistance, root strength, and other characteristics may be better adapted to a continuous corn operation.

Impact on Your Crop

Research has shown that maximizing corn yield potential in continuous corn production systems is challenging compared to rotated systems.¹ A six-year study by the University of Illinois documented a continuous corn yield penalty of 9 to 42 bushels per acre when compared to corn following soybeans. The yield of the continuous corn system decreased year over year for the length of this study. This was attributed to multiple factors including nitrogen (N) availability, corn crop residue accumulation, and weather conditions.¹

Management

Fields selected for continuous corn should have good drainage, high water holding capacity, optimum fertility, no compaction problems, and low insect and disease pressure.¹

Residue

Healthy, high-yielding corn can result in increased levels of residue that can hinder emergence, seedling establishment, standability, and even yield potential of the next crop. Accumulated corn residues can reduce soil temperatures, reduce N availability, increase soil moisture and favour the survival of specific insects and diseases. Appropriate residue management at harvest and at planting is key to successful continuous corn production (Figure 1). To help overcome residue challenges, farmers may need to use intense tillage or strip-tillage to aid in the burial and destruction of residue. Combine attachments or post-harvest shredding can be used to help size and spread residue uniformly. The rate of residue decomposition is influenced by soil temperature, moisture, microbial populations, and N to support microbial degradation of residue. Using strip-tillage and row cleaners at planting can facilitate better seed-to-soil contact and allow soils to warm faster.

Fertility

Another hurdle in continuous corn production is the immobilization of N (N is tied up by microbes to decompose residue from the previous corn crop) (Figure 2).

To overcome this when planting corn following corn, a higher N application rate is often recommended. An additional 30 to 50 pounds of N per acre (34 to 56 kgs N/ha) may be required for continuous corn when compared to a corn-soybean rotation.² The application of N at multiple times throughout the season, such as N applied preplant and as a side dress, may help increase N use efficiency by corn plants in a continuous corn system.

Phosphorous (P) and potassium (K) should also be maintained at optimum levels in continuous corn to encourage stand establishment and help minimize problems with stalk strength and stalk rots. Relative to a typical rotational crop, corn plants use more P and less K than soybean plants. Using a balanced starter fertilizer is more likely to produce a positive response in continuous corn than in a corn-soybean rotation because of the stressful early growing conditions.

Product Selection

Another key for successful continuous corn production is selecting a well adapted corn product. Products should be selected with high characteristic ratings for emergence, seedling vigor, disease resistance, and root and stalk strength. Products with higher emergence ratings have a better chance of pushing through heavy residue, particularly when the residue is keeping soils cool and moist. Prior year residue can harbour pathogens for diseases such as northern corn leaf blight (Figure 3), gray leaf spot (Figure 4), Goss’s wilt (Figure 5) and Diplodia stalk rot (Figure 6); therefore, higher tolerance or resistance to these and other diseases is beneficial for continuous corn production. The likelihood of feeding by certain insect pests during the growing season, such as corn rootworms and European corn borer, is higher with continuous corn. To help protect against these insects, products with multiple modes of insect trait protection for above and below ground insects may be an option. When using these technologies, it is important to practice good stewardship. Corn rootworm is a serious pest and has overcome Bt traits in some regions in Ontario. Consider rotating out of corn after three years of continuous corn, or sooner, to help keep these pests under control.

Seed Treatments

During seedling establishment, seed and seedling pathogens and soil insects, such as wireworms, seed corn maggots and grubs can be a threat, particularly when heavy residue is present. Appropriate seed treatments with fungicide and insecticide protection can help protect seeds and seedlings during emergence and early establishment.

Fungicides

Fungicides applied at VT to R2 growth stages may be beneficial if controllable leaf diseases have been observed during routine field scouting. Fields with heavier disease pressure may require a sequential fungicide program consisting of a pre-tassel application followed by a VT to R2 application. Fields should be scouted near tasselling to determine if a fungicide should be considered. Timely fungicide applications can be an important tool to help limit potential yield losses. Always read and follow fungicide labels.

Weed Control

Continuous corn systems present additional challenges to weed control. Corn residue can reduce the efficacy of many soil-applied herbicides and/or shield young weed seedlings from contact herbicides. A soil-applied residual herbicide should be applied either preplant or preemergence to decrease weed pressure and reduce potential selection of herbicide-tolerant weeds. Providing early season weed control can widen the postemergence application window. For the most effective weed control, postemergence herbicide applications should be made when weeds are small. Additional information for weed control in continuous corn systems can be found at https://www.mixitup.ca/. Control of volunteer corn is especially problematic in continuous corn systems. A proactive management approach is necessary because control options are limited after the new corn crop is established. At harvest, lodged plants, ear drop, improper combine adjustments, and poor harvest conditions can cause grain loss and increase the potential for volunteer corn the next spring. Keeping harvest losses to a minimum and tilling fields in the fall can reduce volunteer corn in the following crop.

Planting

Unless all corn acres are continuous, consider planting corn on corn acres last because residue is likely to keep them wetter and cooler. Increasing seeding rates to offset emergence losses associated with seedling diseases and insects is generally not necessary. The chance of seedling losses may be higher in continuous corn; however, other management practices such as seed selection and quality seed treatments may help reduce seedling establishment issues. Your Bayer representative can help identify the recommended seeding rate for each product. Because corn residue from the previous year may impede seed-to-soil contact, manage the seedbed to reduce residue interference and improve seed-to-soil contact for improved stand establishment.