Chrysanthemum White Rust

Puccinia horiana

Chrysanthemum White Rust

Puccinia horiana P. Hennings 5430720 by Nancy Gregory (CC BY 3.0 us)
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Some green leaves infected with Puccinia horiana
Puccinia horiana P. Hennings 5430720 by Nancy Gregory (CC BY 3.0 us)
1 of 2
Puccinia horiana is a fungal disease that targets Chrysanthemum species, it spreads through airborne spores and thrives in moist, cool conditions. It appears as raised, light-coloured, warty bumps around 5mm in diameter, these are across the underside of the leaves. On the upper surface, these pustules correspond with depressed yellowing of the leaf tissue. Over time these warts turn brown as the disease further infects the plant, leaf health will decline and leaves are likely to distort and die back. Commonly known as Chrysanthemum White Rust, this fungal pathogen originates from Japan, it has now spread throughout Asia, Europe and South America. Heavy infestations can stunt plant growth and reduce vigour, eventually leading to plant death. This problem is most often identified from late summer-autumn, however it is generally active year-round. Chrysanthemum cultivars differ in their susceptibility to this problem. Present in South Africa.
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Symptoms

Raised, light-coloured, warty bumps across the underside of the leaves.
Depressed, yellowing of the leaf tissue on upper leaf surfaces.

Chemical treatment

Fungicides for use on rust diseases of ornamental plants can be used to treat this problem.

Prevention

Monitor plants for early signs of infection. Isolate and dispose of strongly infected plants. Hot water treatments can be effective on dormant plants. All foliage should be removed and the roots trimmed. The treatment involves submerging the plant in hot water for 5 minutes, a temperature of 46 degrees Celcius is recommended. The plants should then be cooled by submerging in cold water and air-dried.
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