HPIPM:Rust

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Pucciniomycotina
Class	Pucciniomycetes
Order	Pucciniales
Suborder	Uredinineae
Family	Pucciniaceae
Genus	Uromyces

Scientific Name

Uromyces appendiculatus

Scientific Name Synonyms

Uromyces phaseoli var. typica

Uromyces phaseoli

Common Name

dry bean rust

Part of Plant Affected

Leaves, stem, pods

Symptoms and Damage

Rust symptoms first appear on the upper and/or lower surfaces of leaves as small yellow or white slightly raised spots. Green pods, and occasionally stems, also may become infected and develop typical rust pustules. These spots enlarge and raise further to form reddish-brown or rust-colored pustules which are about 1/8 inch diameter and contain thousands of microscopic spores called urediniospores (summer spores) which allow the fungus to spread within and between fields. Pustules may be surrounded by a yellow border. Spores are readily released from the pustule and give a rusty appearance to anything they contact. Spores feel 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 severe during early reproductive development of the bean plant. Near the end of the season, many pustules change color, and form dark brown to black teliospores (winter spores) which allow the fungus to overwinter in some production areas. Rust reoccurs next spring when teliospores germinate to form basidiospores which then infect volunteer beans. Infected plants produce pycnia (yellow blisters on the upper leaf surface) and aecia (white cups) on the lower leaf surface or stems near the soil line. Aeciospores move with the wind currents and infect new crop bean plants, resulting in summer spore production. Summer spores are produced in repeating cycles of progressive disease development throughout the summer. Summer spores are moved long distances (regionally) by wind.

Factors Favoring Disease Development

Rust development is favored by cool to moderate temperatures less than 86° F with moisture conditions that result in prolonged periods of free water on the leaf surface. Repeating cycles of summer spore development may occur at 10 to 14 day intervals under favorable conditions. The earlier plants become infected during development, the greater the potential for yield loss. Anything that delays plant maturity, such as hail damage, excess nitrogen, or late planting increases the potential for significant yield loss in the event that environmental conditions favor a rust epidemic.

Management Approaches

1. Plant certified seed of varieties resistant to the prevalent races of rust in the area.

2. Avoid the use of susceptible varieties, especially when planting after June 25, since plants may be exposed to more spore pressure from earlier maturing fields during late August and early September.

3. Incorporate infected bean debris into the soil after harvest and rotate with non-host crops for at least two years. Eliminate volunteer beans the following season.

4. Monitor fields frequently during blossom and early pod development for the initial signs of rust, especially if daily high temperatures are less than 86° F and there is more than 0.25 inches of rainfall per week.

5. Fungicides that prevent or reduce rust infection are more effective when applied early in the epidemic. Thorough coverage is essential.

Moderately to severely rusted bean plants require twice as much moisture from irrigation as uninfected plants to maintain pod set and seed fill.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.