Rust
Rust symptoms first appear as small yellow or white slightly raised spots on the upper and/or lower surfaces of leaves. Those spots enlarge and raise further to form reddish-brown or rust colored pustules which are about 1/8 inch (1-3 mm) in diameter and contain thousands of microscopic spores called summer spores (urediospores). Pustules may be surrounded by a yellow boarder. Spores are released from the pustule readily giving a rusty appearance to anything they contact; they fell like talcum powder when rubbed between the fingers. Severe infection results in premature leaf drop. Pod set, and especially pod fill, can be reduced if infection is sever during early reproductive development of the bean plant. Green pods, and occasionally stems, may also become infected and develop typical rust pustules. Near the end of the season, pustules undergo a subtle change and form dark brown to black winter spores (teliospores), which signify the end of the currnt infection cycles.

Rust development is favored by cool to moderate temperatures with moisture conditions that result in prolonged periods of free water on the leaf surface. Multiple disease cycles may occur at 10-14 day intervals under favorable conditions. The earlier the plant becomes infected during its development, the greater the chance for yield loss. Anything that delays plant maturity, such as hail damage, excess nitrogen, or late planting may increase the potential for significant yield losses in the event that a rust epidemic occurs.

Certified seed of varieties resistant to the prevalent races of rust in the area is used. When late planting is necessary, susceptiblr varieties are avoided. Incorporation of infected bean debris into the soil after harvest and rotation with non-host crops for a least two years is recommended.

Various fungicides are available that can prevent or reduce rust infection if applied early in the epidemic and coverage is thorough. Fields aremonitored frequently during blossom and early pod development for the initial signs of rust. Effectiveness of fungicides will also depend on environmental conditions and irrigation methods. Center pivot systems and frequent rains may wash protectant fungicides off leaves before they can affect the rust spores.