Battle for the Belt: Season 3, Episode 14: Corn Disease

In Episode 14, we talked with Dr. Pierce Paul, Professor and Chair of the Department of Plant Pathology and State Extension Specialist for Cereal Crop Pathology. We discussed common diseases in corn, ear rots, vomitoxin, and crop disease forecasting tools.

Season 3, Episode 14 of Battle for the Belt is now available: https://www.youtube.com/watch?v=OF9Zqn32qe8  

As a recap, in Battle of the Belt and the new Replanting trials, we are evaluating five planting date windows: Ultra early (late March to early April), Early (mid to late April), Normal (early to mid-May), Late (late May-first week of June), and very late (mid to late June). Additionally, we are evaluating contrasting seeding rates and relative maturities in corn.

What are the potential impacts of planting date and seeding rate on corn disease development?

Altering planting date and seeding rate can greatly influence the conditions that favor corn diseases. For example, higher seeding rates create denser canopies, leading to increased humidity within the crop. This will create an ideal environment for many foliar diseases to thrive. Similarly, later planting dates may align the crop’s most susceptible growth stages with mid-to-late summer conditions that are favorable for pathogens like gray leaf spot and tar spot.

“It’s not just about maximizing yield,” Dr. Paul notes. “You also have to consider what environmental conditions your planting decisions may create – and whether they may promote more disease.”

When discussing plant diseases, we often hear the terms severity and incidence. Can you briefly describe what these terms mean?

When scouting fields, it is very important to distinguish between incidence and severity. Incidence tells us how many plants are affected by a disease. For example, if 10 out of 50 plants show disease symptoms, this would be described as 20% disease incidence. Severity tells you how much each plant is affected. As an example, if assessing the ear leaf, and half of the leaf is covered in lesions, we would consider this to be 50% severity (Figure 1). Severity is often a better predictor of yield loss, while incidence tells us how widespread the disease is across a field.

What are the most common diseases we see affecting corn here in Ohio?

The top corn diseases to watch out for in Ohio include:

• Gray Leaf Spot – consistently prevalent across the state.
• Northern Corn Leaf Blight – weather dependent.
• Tar Spot – growing concern, especially in Northwest Ohio.
• Rusts – common and southern rust, more likely in southern regions.
• Ear Rots – including Gibberella and Fusarium ear rots, which can lead to grain contamination with mycotoxins.

Several ear rots will lead to the production of mycotoxins. What are some of those mycotoxins, and discuss why they could potentially lead to further issues post-harvest?

Some ear rot diseases produce mycotoxins, which can be harmful to livestock and reduce grain marketability. Key toxins in Ohio include:

• Deoxynivalenol (DON) or “vomitoxin” – causes feed refusal and performance issues in swine.
• Zearalenone – mimics estrogen and disrupts animal reproduction.
• Fumonisins – a concern for horse health.
• Aflatoxins – produced under drought-like conditions, can be a threat to human and animal health.

These contaminants pose challenges both on-farm and during grain marketing. Awareness and management are key.

When should farmers consider applying fungicides, and how do they determine the optimal timing?

Fungicide timing depends on disease pressure, hybrid susceptibility, and weather conditions. In high-risk situations – wet years, delayed planting, or disease history in the field there are a few recommended management strategies:

• Targeting application at the R1 stage (silking) for most foliar diseases.
• Selecting products based on the primary diseases of concern.
• Considering whether your hybrid is susceptible or resistant.

Fields near woods or rivers also tend to have higher disease pressure and may benefit more from fungicide applications.

What are disease forecasting models, and how can they be utilized to our benefit?

Disease forecasting models use weather data to estimate the risk of certain diseases developing. There are models available on the Crop Protection Network for gray leaf spot and tar spot, with additional tools in development for vomitoxin risk assessment.

Models can help you decide whether a fungicide application is worth the investment. These tools look at weather conditions leading up to key growth stages and calculate the risk of disease development or grain contamination with mycotoxins (forthcoming).

Resources Available for Further Reference

• Crop Protection Network (CPN) – Fungicide Efficacy for Control of Corn Foliar Diseases: https://cropprotectionnetwork.s3.amazonaws.com/corn-foliar-efficacy-2025.pdf
• Ohio State University Extension Corn Disease Fact Sheets – Printable guides to help identify and manage common foliar and ear diseases: https://ohioline.osu.edu/topic/ag-crops-and-livestock
• Corn Disease Forecasting Models – Real-time disease risk assessments. Available through the crop protection network. https://cropprotectionnetwork.org/crop-disease-forecasting
• Contact an OSU Extension Specialist – Reach out to your local Extension educator, field specialist, or crop pathology expert for field-specific recommendations: https://extension.osu.edu/directory/?f%5B0%5D=sm_field_ext_program_area%3Aagnr

Field & Crop Progress Updates

Planting is complete! Last week, the soil dried out and was adequate for planting across many locations in Ohio, including our three research stations. This resulted in all three locations planting the fifth and final planting date for the study (Table 1).

Across all planting dates, both corn and soybeans are progressing well with the extended period of heat the state has seen recently. Planting date one soybean at each location has entered the reproductive stages and is now presenting flowers (Figure 2). Corn from planting date one is currently at the V9 to V10 growth stage, entering a period of rapid growth and biomass accumulation.

At the Northwest location, soybean planting dates one and two are at the R2 and R1 stages, while planting dates three and four remain in the V4 and V2 vegetative stages. Corn growth stages from planting dates one through four at this site are V9, V8, V6, and V4, respectively.

The Western and Wooster locations are seeing similar growth stages for both crops; specific stages by planting date are summarized in Table 2.

Keep following the ‘Battle for the Belt’ this growing season to learn more and get further updates! You can find the full video playlist of Battle for the Belt on the Ohio State Agronomy YouTube channel.