An ear rot problem usually begins before the combine reaches the field.
Weather around silking, insect injury, hail, hybrid susceptibility, crop residue, and plant stress all influence which fungi infect the ear. By August, the grower’s job is less about preventing the original infection and more about identifying affected fields, understanding the likely toxin risk, and changing harvest and storage plans before damaged grain becomes a larger problem.
Ear rots are not all the same.
Some are favored by hot, dry conditions. Others increase under cool, wet weather. Several can produce mycotoxins, while others mainly reduce grain quality. Mold color alone is not always enough for a firm diagnosis, but the location and pattern of growth provide useful clues.
Waiting until harvest can be costly.
Open ears while the crop is still standing. Begin in areas with known stress:
Walk in a pattern that covers the whole field. Do not inspect only end rows or visibly damaged plants.
Peel back husks and examine the tip, base, and sides of the ear. Note mold color, kernel injury, husk condition, and whether the mold begins at wounds or follows a consistent pattern.
Collect representative samples for laboratory confirmation where grain safety is in question.
Aspergillus ear rot deserves attention after hot, dry weather, especially where drought stress occurs after pollination.
The fungus often colonizes kernels near the ear tip or at insect-damaged areas. Aspergillus flavus commonly produces olive-green or yellow-green powdery spores. Other Aspergillus species may appear darker.
The major concern is aflatoxin.
Drought-stressed corn, nonirrigated corners, and ears injured by insects are especially vulnerable. Nebraska Extension notes that hot, dry conditions combined with wind and insect damage increase Aspergillus risk and that the disease is more common in drought-stressed corn.
The presence of mold does not tell you the toxin concentration. Grain must be sampled and tested.
Aflatoxin can be distributed unevenly, so a poor sample may miss contaminated pockets. Follow approved grain-sampling procedures and use a qualified laboratory.
Fusarium ear rot can develop under a wide range of conditions.
Symptoms commonly appear as scattered white, pale pink, or salmon-colored mold on individual kernels or groups of kernels. Infection frequently occurs where insects, birds, or hail have damaged the ear.
Some kernels develop a “starburst” pattern—white lines radiating from the kernel cap.
Fusarium species may produce fumonisins, which create livestock and grain-market concerns. The risk varies by species, environment, and grain handling.
Because infection can be scattered, Fusarium may be less obvious than a solid mat of mold. Pull ears from several areas and look closely at damaged kernels.
Gibberella ear rot is often associated with cool, wet, or humid conditions around silking and early grain fill.
White mold develops near the ear tip and may turn pink or reddish as it spreads toward the base. In severe cases, husks adhere tightly to the ear.
The pathogen can produce deoxynivalenol, commonly called DON or vomitoxin, and zearalenone.
Fields following corn or wheat may carry more inoculum because the fungus survives in residue from both crops. Rain splash and wind move spores to silks.
Nebraska Extension describes Gibberella as a tip-initiated white-to-pink or red mold favored by cool, humid conditions, with the potential to produce DON and zearalenone.
Do not assume red mold is only a quality issue. Test grain intended for feed or sale where infection is meaningful.
Diplodia ear rot often produces dense white or gray mold between kernels and husks.
Infection frequently begins near the ear base and moves toward the tip. Severely affected ears may become lightweight and mummified. Small black fungal structures can develop on kernels, cobs, or husks, giving the surface a rough appearance.
Diplodia is favored by wet conditions around silking and is more common in continuous corn or fields with abundant infected residue.
Unlike Aspergillus, Fusarium, and Gibberella, Diplodia has not generally been associated with mycotoxin production in U.S. corn. It can still create serious losses through reduced test weight, fines, poor storability, and dockage.
A nontoxigenic mold is not harmless in storage.
A field may experience weather favorable for an ear rot without developing a major problem.
Hybrid resistance, husk coverage, ear orientation, insect control, residue, crop rotation, planting date, and plant health all affect infection.
Insect wounds are particularly important. Damaged kernels provide entry points and expose nutrients to fungal growth. Ear-feeding insects can also carry spores as they move.
Hail creates similar opportunities.
Drought weakens the plant and may loosen husks around the ear tip. Wet weather can prolong silk exposure, increase spore movement, and slow ear drying.
The disease is the result of the host, pathogen, and environment interacting. Weather raises or lowers risk, but field scouting determines whether that risk became a problem.
Ear rots and stalk problems often occur together.
A plant supporting a diseased ear may also have suffered drought, nutrient stress, leaf disease, or root injury. As grain fills, the plant may pull carbohydrates from the stalk, leaving it vulnerable to stalk rot and lodging.
Use the pinch test on lower internodes and push plants away from the row. Plants that crush easily or fail to return upright should be considered for earlier harvest.
Record whether weak stalks occur in the same areas as ear mold.
A field with both ear rot and lodging risk may need to move to the front of the harvest schedule even if grain moisture remains higher than preferred.
Harvest order can reduce losses.
Fields with significant ear rot should generally be harvested before cleaner fields. Delaying allows mold to progress, ears to drop, stalks to lodge, and grain to experience repeated wetting.
The cost of drying wetter corn may be less than the cost of losing contaminated or lodged grain.
Keep affected grain separate where practical. Mixing moldy grain with clean grain can spread fines and contamination and make the entire lot harder to market or manage.
Do not blend grain to avoid legal, contract, or safety limits. Follow current regulations and buyer requirements.
Moldy kernels and damaged ears often produce more fines.
Combine settings should remove as much lightweight material as practical without throwing away sound grain. Fan speed, sieve settings, rotor or cylinder speed, and ground speed may need adjustment.
Inspect the grain tank frequently.
A field that appears manageable from the ear can produce a high percentage of cracked kernels and fines after shelling. Those materials concentrate mold, restrict airflow in the bin, and increase spoilage risk.
Clean grain improves storability.
Warm, wet grain allows fungi to continue growing.
Dry affected corn promptly. Do not allow wet loads to remain in trucks, carts, or holding bins longer than necessary. The exact safe moisture depends on storage duration and temperature, but moldy grain generally deserves more conservative management than sound grain.
Nebraska Extension recommends drying and cooling affected grain quickly, storing only the highest-quality grain for long periods, and avoiding mixing severely affected grain with clean grain.
Aeration should cool grain uniformly. Monitor the center and surface of the bin, not only the exhaust air. Check for crusting, condensation, heating, and odors.
Fines tend to accumulate in the center of the bin and reduce airflow. Coring the bin after filling can remove part of that concentration.
Mycotoxins are rarely distributed evenly.
A few highly contaminated kernels can be mixed into a large amount of cleaner grain. This makes sampling the largest source of testing error in many situations.
Take multiple incremental samples from moving grain when possible. Combine them into a representative composite and follow the laboratory’s required sample size and preparation.
A scoop from the top of one truck is not a reliable representation of an entire field.
Separate samples by field or storage unit. Combining several fields can hide the source and complicate marketing decisions.
Laboratory identification of the fungus and laboratory measurement of a toxin are different services. Confirm what the lab will provide.
Moldy grain produces dust containing fungal spores and fine particles.
Use properly fitted respiratory protection during harvest, unloading, bin entry, cleaning, and handling. Keep cab filtration systems maintained. Minimize exposure when opening husks in heavily affected fields.
Never enter a grain bin without following confined-space and grain-engulfment safety procedures.
The urgency of harvest does not reduce the hazard.
Once an ear rot is visible in August, fertilizer cannot remove the fungus or destroy an existing mycotoxin.
Late nutrient applications may improve color in some plants, but they do not sanitize kernels. Applying fertilizer in response to mold distracts from the decisions that can still reduce loss: harvest timing, segregation, drying, cooling, testing, and safe feeding or marketing.
Balanced fertility earlier in the season can support plant strength and reduce stress, but excessive nitrogen, potassium shortage, poor pH, and other imbalances must be addressed through a long-term program.
Do not use a crop-health product as a substitute for disease identification.
After harvest, compare disease locations with weather, hybrid, planting date, insect injury, residue, and soil conditions.
Where one hybrid is consistently affected, review resistance ratings. Where infection follows continuous corn residue, consider rotation and residue management. Where pivot corners or sandy ridges show Aspergillus, review drought management and insect scouting.
Where wet low areas develop Gibberella or Diplodia, examine drainage and hybrid selection.
Save photographs and laboratory results. “Moldy corn” is not enough detail for future decisions. Record the specific disease and toxin where confirmed.
Supply Solutions can help growers review soil and fertility factors that may have contributed to weak plants, but fertilizer is not the August treatment for an infected ear. Contact the company when building the next crop’s nutrient program, while relying on crop-disease specialists, laboratories, and grain handlers for immediate ear-rot and mycotoxin decisions.
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