How to Manage Pests

Pests in Gardens and Landscapes

Seasonal development and life cycle—Rust fungi

Rust fungi infect under mild, moist conditions. Rusts are spread primarily by windblown or water-splashed spores. In addition to orangish pustules, many species also form black overwintering spores on leaves in the autumn, which start the disease cycle in the spring. Each type of rust is specific to certain hosts. Many species have complex life cycles, alternating generations between two host species. Certain rusts that can kill pines alternate their life cycle between pines and other hosts, such as Ribes (currant and gooseberry) or oaks. These rusts usually do not harm their alternate hosts. Others, such as the rose rust, Phragmidium mucronatum, are apparently restricted to one host species.

Spores of rose rust
Spores of rose rust

Statewide IPM Program, Agriculture and Natural Resources, University of California
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