Disease 3 - Rust on Rosa and Fuchsia

Above photo showing rust on the undersurface of fuchsia leaf from Botanic Gardens

Above is a close up of rust fruiting bodies through a hand lens. Fungus within the leaf produces stalks with spores on the end, with the continued growth of these stalks bursting the epidermis of the leaf in that area. The masses of spores are then blown about by the wind. 

Below are photos showing what rust looks like on both sides of rose leaf.

Rust is a collection of fungal diseases that refers to the orange-brown spore masses which are produced on affected plants. There are a large number of different fungal rust species which all lead to the presence of rust disease on susceptible plants. 

Host Range : ornamentals, fruit, vegetables, field crops and weeds. Generally a particular species of rust can attack only certain host species, but there are some special species of fungal rust that can attack different genera. 

Symptoms : Leaves, stems and fruit can be attacked. 

On leaves, the upper surface becomes speckled with small yellow patches which can coalesce. On the under surface there are corresponding orange-brown or rusty spots. In heavy infection there may be premature defoliation and serious weakening of plant. 

A few rusts stimulate plants cells to grow into gall-like structures (eg. acacia)

Disease Cycle : Rust can overwinter as thick walled spores on infected plants, on debris from infected plants, within the soil and on seed. Wind can blow the spores onto new hosts. Can also be spread from water splash from infected host plants. Generally speaking, most rusts favour high humidity, but vary in their preference for temperature. 

Control : 

cultural : avoid planting too thickly, avoid overhead irrigation in rusts that favour moist conditions, use resistant varieties (although this can cause emergence of new strains), do not vegetatively propagate from diseased plants or use seed from these plants, remove and burn diseased plants and prunings, control susceptible weed species.

chemical : copper or sulphur-based sprays (sulphur based can cause scorch on some plants in temperatures over 30 degrees celsius ). Most widely used fungicide is mancozeb. 

Reference : Kerruish, G-36

                     McMaugh, pg. 277