By Craig Allaman, Lead Agronomist, Cornelius Seed 

As harvest approaches, you may notice some corn fields taking on a black or sooty appearance. With the corn crop drying down rapidly over the last couple of weeks and the warm, moist conditions we’ve experienced, we expect saprophytic fungi to be fairly active this fall. 

While seeing black corn can be concerning, in many cases what you’re seeing is part of the natural breakdown of dead plant material. 

What Are Saprophytic Fungi? 

Saprophytic fungi are microorganisms that colonize and feed on dead plant tissue. As the corn plant reaches maturity and dies, there is more dead tissue available for these fungi to colonize. 

Warm temperatures combined with moisture, humidity, fog and heavy dew can create favorable conditions for their growth. That means fields that have died down quickly followed by warm, damp weather may show significant fungal growth on leaves and husks. 

The result can be corn plants that appear black, dirty or covered in a dark, dusty material. 

Is Black Corn a Cause for Concern? 

The appearance can look alarming, but saprophytic fungi themselves are not pathogens of corn. Their role is to help break down dead plant material. 

Iowa State University Extension notes that these fungi are not known to produce toxins, and harvested grain from affected plants should generally look relatively clean. 

Harvesting heavily colonized fields can, however, create a considerable amount of dark, moldy dust as the combine moves through the dry plant material. 

Don’t Confuse It With Tar Spot 

One important consideration is distinguishing saprophytic fungal growth from tar spot. 

Tar spot typically produces distinct, irregular-shaped, raised black spots on corn leaves. Saprophytic fungal growth tends to have more of a fuzzy, dusty or out-of-focus appearance across dead plant tissue. 

If you’re unsure what you’re seeing, take a closer look at the affected leaves and talk with your Cornelius Seed agronomist or Seed Rep. 

Be Mindful of Dust During Harvest 

Fields with heavy saprophytic fungal growth may produce significant amounts of dust and fungal spores during harvest. 

Growers with allergies or respiratory concerns should take extra precautions to limit exposure to this dust. Keeping combine engine and cab filters clean is also important when harvesting heavily affected fields. 

What Should Growers Do? 

For most growers, the key right now is simply knowing what you’re looking at. 

We expect conditions this fall may make saprophytic fungi more noticeable than usual. If your corn begins looking black as it dries down, don’t immediately assume you’re dealing with a new disease or a grain-quality problem. 

Scout the field, examine the affected tissue and distinguish between saprophytic fungal growth and diseases such as tar spot. 

For additional photos and information on identifying saprophytic fungi, read Iowa State University Extension’s “Why is my corn black?” 

If you have questions about what you’re seeing in your fields as harvest approaches, contact your Cornelius Seed agronomist or Seed Rep. 

Plant It. Profit.