Symptoms
Rusty-orange to brown, powdery clusters of spores on the underside of leaves, matched on the upper side by yellow spots. Heavily infected leaves turn yellow and drop prematurely, and the plant weakens. It affects roses and mallows among others, and some rusts have an alternate host (for example pear rust and juniper).
Treatment
Remove and destroy infected leaves and improve air circulation. Apply fungicides in cases of heavy infection. With host-alternating rusts it is worth avoiding the proximity of alternate hosts.
Prevention
An airy site, watering at the base, avoiding wetting the leaves, choosing resistant varieties, and raking up and removing fallen leaves in autumn.
Sources
- Atlas of plant diseases
