Why Some Corn Fields Appear Black This Fall

As you drive through parts of the state this fall, you may notice corn fields with a black appearance, particularly on the husks and leaves. Based on past experience, producers can also expect black dust clouds behind combines and extremely dirty harvest equipment.

This phenomenon is caused by microscopic fungal spores that are released when plant material is disturbed during harvest.

Although foliar diseases such as tar spot, northern corn leaf blight and other fungal diseases were common across the state this growing season, they are not responsible for the widespread black appearance of corn fields seen this fall. Instead, the dark appearance results from saprophytic fungi colonizing dead corn tissue. Saprophytic fungi feed on dead plant material and do not infect healthy plant tissue.

One of the most commonly observed saprophytic fungi is Alternaria spp. While these fungi can cover leaves and husks with dark spores, they typically do not damage the ear or grain beneath them.

The warm, wet conditions experienced during September created an ideal environment for these fungi to grow and produce spores.

No Additional Crop Management Needed

Because saprophytic fungi colonize dead tissue and do not cause further crop damage, no additional management is needed in affected fields.

However, precautions should be taken to protect yourself from the dust and spores released during harvest. Exposure can cause respiratory irritation and, in some cases, more serious health issues.

Combine Maintenance

Air Filters

• Inspect cab air filters regularly, potentially on a daily basis when dust levels are high.
• Clean or replace filters according to manufacturer recommendations.
• When replacing filters, ensure all gaskets are in good condition and properly installed so cab air remains well filtered.

Fan Settings

• Make sure the heating, ventilation and air conditioning (HVAC) system is operating at the appropriate blower settings to maintain positive cab pressure and reduce dust entry.

Door Seals

• Inspect door gaskets and seals to ensure the cab door closes tightly.
• Proper seals help prevent dust and spores from entering the cab.

Adjust Combine Settings

Proper machine adjustments can reduce grain damage and minimize dust production. Consider evaluating:

• Deck plate settings
• Gathering chain speed
• Feed accelerator speed
• Rotor or cylinder speed
• Concave clearance
• Concave type

Personal Protection

Individuals with Existing Respiratory Conditions

People with asthma, Farmer's Lung, chronic respiratory diseases or existing respiratory infections should make every effort to avoid dust exposure.

Monitor symptoms closely and leave dusty environments if symptoms worsen.

Reduce Exposure Whenever Possible

• Stay inside the cab during harvest and unloading operations whenever practical.
• When working outside, position yourself upwind of dust sources whenever possible.

Wear a Properly Fitted Respirator

• Wear a NIOSH-approved respirator with two straps (such as an N95) when dusty conditions cannot be avoided.
• Ensure the respirator fits properly and forms a tight seal around the face.
• Individuals with heart or lung conditions should consult a healthcare provider before using a respirator.
• More information is available on the Personal Protective Equipment page from the University of Nebraska Medical Center's College of Public Health. 

Seek Medical Attention When Needed

If you spend an extended period in a dusty environment and begin feeling ill within several hours, seek medical advice promptly.

Health conditions associated with exposure to agricultural dust include:

• Farmer's Hypersensitivity Pneumonitis (Farmer's Lung)
• Organic Dust Toxic Syndrome (ODTS)

Symptoms may resemble influenza and include:

• Cough
• Chest tightness
• Fever
• Chills
• Fatigue
• Shortness of breath

Because treatment differs from that of influenza or other common illnesses, early recognition and medical evaluation are important.

Resources

• Human Health Concerns from Grain Dusts and Molds During Harvest, Purdue University