Common Rust, Common Smut And Disease Mimics Developing In Corn

 

Most of the corn in the state is at tasseling. This growth stage is also when most common fungal diseases begin to develop. Currently, common rust and common smut are the main diseases being found in corn.

 

 

Common rust is a minor disease of corn in South Dakota. This disease can be found almost in every corn field. The disease develops from spores blown in from southern states as the common rust pathogen does not survive in South Dakota. Typical symptoms of common rust are small, dark, reddish-brown raised pustules on a corn leaf. The pustules vary from oval to elongated shape (Figure 1). Older leaves especially along the field edges can have moderate levels of common rust.

 

 

Common smut was found at very low incidence in a few corn fields in Brookings and Codington counties. Common smut can develop on any part of the corn plant especially if the young growing tissues are injured by hail, insect feeding, and other injuries. A smut gall is composed of a mass of black, greasy, or powdery spores enclosed by a smooth, greenish-white to silvery-white membrane (Figure 2). As the spores mature, the outer covering of the gall becomes dry and papery and disintegrates, releasing the spores (teliospores). The released teliospores fall to the ground and become the overwintering inoculum for the next growing season. Common smut can be managed through seed treatment, but infections that happen later in the season will not be controlled by a seed treatment.

 

 

 

Plants with symptoms resembling those caused by biological agents were observed in a few fields (Figure 3 and Figure 4). These symptoms are caused by genetic abnormalities and do not spread from plant to plant.