I was asked about rust in some oats east in the county. These oats are coming along, getting closer to graze. It has been a little dry here, and many aphids are present. Tip burn is showing up where temperatures dropped. Once we started looking through the field, it was apparent spots on the leaves were the result of aphid feeding. We still need to scout for aphids since they vector barley yellow dwarf virus (BYD). Many times, aphids feeding will leave a small, circular red spot. This appears different than rust since the rust postule is raised from the leaf.
Crown rust is something we see more in our area south. Like rust we see in wheat and corn, the spores are carried by wind and move long distances easily. The spores overwinter in warmer southern climes and come back to our region in the summer. Rust is identified on the leaf by the small pustules which contain orange-yellow spores. Though grazing and grain are managed differently, UGA Extension Forage Scientist Dr. Dennis Hancock says rust can reduce yields in grazing. If rust is present, it is recommended to grave heavily to reduce the amount of fungal inoculant on the oat crop. We would also have to monitor this close grazing.
The key to differentiating rust from leaf spot or aphid feeding is the orange powder spores on your finger after rubbing the leaf. Here is a photo of rust from Seminole County Agent Rome Ethredge: