Rusts

    Rusts

    Many fungal species

    rust

    Rust on hollyhock (Claudia Nischwitz, Utah State University Extension)

    rust

    White pine rust on Ribes (Robert L. Anderson, USDA Forest Service, Bugwood.org)

    rust

    Fir broom rust (Joseph O'Brien, USDA Forest Service, Bugwood.org)

    Hosts, Symptoms & Signs

    • many hosts; commonly seen on hollyhock, roses, hawthorn, flax, cottonwoods and fir (at higher elevations)
    • rusts are very host specific and rarely kill the host plant
    • orange blisters occur on plant tissue at infection points
    • ruptured blisters release orange-colored spores that can cause new infections
    • deformed growth in conifers
    • early defoliation can occur in deciduous trees

    Disease Cycle

    • overwinter on living host material
    • in spring, spores are wind dispersed over great distances
    • the disease cycle is typically completed on one or two hosts
    • rust is an obligate parasite and requires a living host

    IPM Recommendations

    • Manage trees to improve or maintain overall health.
    • Use resistant plant varieties when available.
    • Remove alternate hosts to break the disease cycle.
    • Remove infected plant material to prevent spread to uninfected plants and to prevent overwintering.
    • Plant farther apart to allow for air movement and a reduction in humidity.
    • Apply a preventative fungicide (chlorothalonil; myclobutanil; tebuconazole) to protect healthy leaves.
    • Leaves with fruiting structures (orange blisters) cannot be saved.