How to Manage Pests

Pests in Gardens and Landscapes

Rusts

Rusts are fungal diseases that infect many hosts, including birch, cottonwood, cypress, false cypress, fuchsia, hawthorn, juniper, pine, poplar, rhododendron, rose, and spruce. Dry reddish, yellowish, or orange spore masses or pustules form on infected tissue, especially on the lower surface of leaves. The upper surface of heavily infested leaves turns yellow or brown and infected leaves may drop prematurely. Orange, gelatinous masses appear on some infected evergreen hosts. Some species cause tissue swellings or galls, colorful spots on plants, or cankers on bark. These can cause branch dieback and occasionally kill the entire plant. Some rusts may cause leaves and shoots to become distorted, dwarfed, and discolored, forming "witches' brooms."

Life cycle

Solutions

Avoid overhead watering, which favors spore germination. Rake infected leaves or needles and clip and dispose of infected shoots and branches as soon as they appear. Fungicides applied in the spring can reduce some rust diseases, but the frequent applications required to provide good control are generally not warranted in landscapes. To control white pine blister rust, nearby alternate hosts (Ribes spp.) are sometimes removed, but the effectiveness of this is questionable.

rusts
Rust spores on rose leaves

rdwestgallrustRound western gall rust swellings


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