This fungal disease appears as a black powdery coating on leaves and is caused by one of several different sac fungi (Ascomycetes), often Cladosporium and Alternaria. The appearance on corn is usually due an infestation of aphids that supply a honeydew secretion that the fungi use to live and multiply. Although the sooty mold is unsightly and blocks sunlight, it usually does not do significant damage to the plant.
- Wash or spray the leaves with 1 tablespoon dish soap or insecticidal soap per gallon of lukewarm water.
- Control the aphid infestation by:
- Using row covers
- Blasting with a water hose
- Spraying with Neem (avoid contaminating water or spraying beneficial insects especially bees)
- As last resorts for very severe infestations spray with sulfur or pyrethrin, heeding cautionary warnings on the containers