Page 88 - AG 7-2011 Revised 2016

Rust of Rose Rust of Rose

Photo Courtesy of UNIVAR Photo Courtesy of UNIVAR

LEAF SPOT

Photo Courtesy of Corky’s Pest Control
Brian Rineberg

RUST
Rusts infect many plants including junipers, pines and especially roses. This fungus will form
dry, orange colored spore masses on the underside of the leaves, and discolor the upper side
of the leaves. Moderate infestations of rust pustules on the underside apparently do not do any
harm. The upper surface of heavily infested leaves turn yellow or brown and the leaves may
drop prematurely. Plants generally can weather one season of a rust outbreak.
Rust is primarily spread by windblown or water-splashed spores. Each type of rust is specific to
certain hosts. Rust fungi infect under mild, moist conditions. Warm, humid weather increases
the rust outbreaks.
Since rusts are fungi, similar to powdery mildew; the treatment practices are the same. Just
remember as a general rule that fungus relates to water. Reduce water and you may possibly
reduce the risk of your plants being affected by a fungus.
Because fungi are seasonal, the best control is prevention before they take hold rather than
trying to control after the fact.
LEAF SPOT
Bacterial leafspot is noticed as small, water-soaked spots that are visible from both sides of
a leaf. The spots usually are limited by leaf veins and have an angular, square, or rectangular
appearance. They rapidly turn brown and with aging may dry out and become papery and tan.
Lesions tend to be relatively small (less than 0.25 inch in diameter) and restricted to leaves.
Leaf Spot is a seed-borne bacteria. It can spread rapidly via splashing water such as sprinkler
irrigation. Disease development is favored in warm, moist conditions. Infected transplants will
carry the bacteria into production fields.

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