In the plant world, rust is the common name for several fungal diseases that affect turfgrasses like zoysia and St. Augustine, ornamental plants like gladiolas and daylilies, and edible plants like corn, beans, and squash.
The first sign of a rust infection is typically small white, yellow or orange spots that appear on the leaves, typically during the cooler months. As the disease advances, the leaves may develop lesions that turn yellow, brown, or even black, and may eventually fall off.
For help diagnosing a plant that may be affected by rust, take a sample in a sealed bag to your county Extension office.
Prevention through garden sanitation is the best strategy, but rust may be treatable with an approved fungicide, if the disease is caught early enough.