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Rhododendron Rust


Rhododendron Rust

Usually appear in

Spring to Autumn.

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Caused By:-     Mainly Chrysomyxa species of Fungi


Chrysomyxa rhododendri on Spruce tree. Picture by Joseph O'Brien, USDA Forest Service,
Rhododendron Rust is mainly caused by fungi from the genus Chrysomyxa. Many of these had been identified as Chrysomyxa rhododendri. Like most rust fungi it requires two species to complete its life cycle. The other species is mainly Spruce from the genus Picea. The top leaf surface shows signs of yellowish leaf mottling with corresponding Orange-red pustules containing spores on the lower surface of the leaf.
The rust develops when spores land on the plant in spring from Spruce trees and continues to infest the leaves until they fall off in autumn. In mid-summer the orange pustules on the bottom of the leaves contain spores that will release and spread the fungus by wind to infect Spruce.
Usually, but not always, the fungus on one specie does not infect that specie, but its companion host in this case trees from the Genus Picea.
See also these other rusts Anemone, Antirrhinum, Bean, Bluebelle, Cedar Quince, Chrysanthemum White, Fucshia, Gladiolus, Gooseberry, Hollyhock, Juniper Pear, Mahonia, Mint, Pear Juniper, Pelargonium, Periwinkle, Plum, Potato Internal, Quince, Rose, Rust, White.


As with any fungal disease one of the best ways of preventing it is by good hygiene. Remove all dead leaves in autumn to prevent the spores from over wintering. If the leaves is from an infected plant burn them.
Check plants regularly and remove infected leaves by hand as soon as they are seen and then spray with a suitable fungicide. Spray the plant and the soil around it with a fungicide suitable for the control of rust fungus.
Water the compost of susceptible plants directly trying not to wet the foliage.
Maintain an open structure to allow good air circulation through the plant and ensure greenhouses are always well ventilated.
Often there are resistant varieties of the plant you wish to grow.
Try not to grow Rhododendron near Picea(Spruce) species.

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