Rust

Puccinia and Uromyces species

The various species of these fungal diseases affect a wide variety of crops including asparagus, beans, corn, onion and spinach. Rust usually starts out as yellow or whitish spots on the top sides of the leaves. The distinctive bright reddish or yellowish spores that give the plant its name appear later, as pustules on the undersides of the leaves. The leaves commonly turn yellow, the plant grows slowly and becomes stunted, and in severe cases it eventually dies.

Rust is spread by wind borne spores and can travel long distances, but you should still remove infected leaves and crop debris to minimize local sources of infection. Ideally use drip irrigation to keep leaves dry and make sure air circulation is good. If you must use overhead irrigation, water in the morning or early evening so the leaves have a chance to dry out before nightfall. To minimize the effects of the disease keep the plants well fed and watered, but don’t give them too much nitrogen.

Image: William M. Brown Jr., Bugwood.org