Rust Symptoms on the Southern Pea

Types of Rust

• Common bean rust infects plants globally. It occurs in most varieties of dry and snap beans, particularly in areas where abundant moisture and high humidity create optimal conditions for the rust pathogen. A parasitic fungus that lives its entire life on its host, it cannot survive on its own.

  Asian soybean rust infected the Orient for decades, but farmers in the continental United States reported no cases until November of 2004. Evidence suggests that the disease crossed from South America to the United States on the winds of Hurricane Ivan, in September of that year.

Symptoms

• In the beginning stages of the disease, bean rust spores infect the undersides of the lower leaves of a plant. The spores may be circular or cone-shaped and have a rusty brown, red, gray, tan or yellow hue. An observer may need a magnifying glass to detect newly-formed spores. The top side of the leaves may show no symptoms, or they may display tiny yellow specks that appear insignificant to gardeners.

  As the disease progresses, spores grow larger and may join other spores to form large lesions. Common bean rust lesions may blacken as the disease develops. Leaves may yellow and die off. The lesions spread to both sides of the leaves and the pods. In serious cases, yields may decrease by as much as 80 percent.

Prevention

• Since southern peas serve as preferred hosts for Asian soybean rust, purchase seeds that are rust-resistant, particularly if you live in areas where bean rust proliferates. Use certified seed treated with a fungicide and avoid planting beans in the same spot each year.

  Other preventative measures include planting in well-drained soil that will not allow the plant roots to remain wet. Water plants at the surface of the ground, rather than from overhead, to keep leaves dry. Lastly, remove all debris from the garden after you harvest the beans. Rust may survive the winter attached to the debris and infect new plantings in spring.

Treatment

• While preventative measures may decrease your chance of the disease infecting your crops, once rust has occurred, fungicides may provide the only solution. If the disease is in its early stages, two applications of fungicide might alleviate the problem. Apply the fungicide at the earliest stage of the disease, then again after seven to 21 days, depending upon label directions.

  Foliar sprays containing sulfur can reduce the disease's devastating effects. Rust may prove more troublesome in fall than in spring, but gardeners must show vigilance at all times, especially if they grow southern peas in an area of known infestation.