Growers are reporting the appearance of black to gray discoloration or “dust” on corn plants. In some cases, large amounts of black “dust” have been reported from combines during harvest, sometimes looking like a cloud of smoke following the combine. The large amount of microscopic spores produced by some fungi can cause this phenomenon.

Diseases such as common smut have been common this year and could have contributed to the appearance of these spores. In addition, the late season rainfall has created a favorable environment for other common fungi to flourish and rapidly produce copious amounts of spores. Some of these fungi, such as Alternaria spp., grow on dead plant tissue, like corn husks, but don’t typically cause damage to the ear underneath (Figures 1a and 1b).

No management is necessary for this issue and it’s not expected to damage the corn, although dust masks may be advised for those who are prone to respiratory issues and sensitive to particulate matter. (For more information see Sept. 23 CropWatch article, Protect Your Lungs with Properly Fitted Respiratory Masks.)