While it may be very concerning to see a cloud of black dust following the combine when picking corn this year, this dust is not something that normally impacts the grain or grain quality. The black cloud is the caused by fungal spores that have formed on the dying leaves and husks. The main types of fungi causing this phenomenon are common smut (Figure 1) and several saprophytic, weak, parasitic fungi, such as Alternaria, Cladosporium, and Aureobasidium.

An ear of corn lays on the ground, and it has a fungi called common smut. The fungi is black and grey, and forms as circular bulbs.
Figure 1. Common smut on corn.

Plants affected by these fungi have a sooty appearance, which usually occurs when the crop is mature and wet, such as when humid weather occurs. Stressed plants may be more prone to infection by these sooty molds.

Corn leaves that are affected by saprophytic fungi. The leaves appear discoloured in shades of grey, black and yellow, and looks sooty.
Figure 2. Saprophytic fungi on mature corn leaves.

Occasionally, the sooty molds may infect the kernels, giving them a black appearance. If kernel infection is extensive, the grain should be thoroughly cleaned to remove light, damaged, and moldy kernels. Store the grain at 15% moisture content with proper air movement through the bin. Checking the grain on a regular basis is recommended.

The head of a combine is cutting corn. A dusty cloud is coming up from the field, which is happening due to saprophytic fungi in the corn.
Figure 3. Dust surrounding the combine head because of saprophytic fungi on corn.
A combine drives in a field cutting corn. A dark dusty cloud is coming up, which is happening due to saprophytic fungi in the corn.
Figure 4. Dust produced from harvesting corn with saprophytic fungi.

Black dust caused by saprophytic fungi primarily annoys farmers harvesting corn and contributes to beautiful red sunsets while causing little impact on grain quality or yield. Combines may become covered with the sooty black dust, which may require additional maintenance checks. Combine operators should ensure that the engine filters are clean to prevent further issues such as overheating. While harvesting, it is recommended for anyone prone to respiratory issues to wear a dust mask as a precaution.