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Pelargonium Rust


Pelargonium Rust

Usually appear in

All Seasons

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Caused By:-     The Fungus Puccinia pelargonii-zonalis


This is the fungus on the underside of the leaf. This fungus is specific too Zonal Pelargoniums Ivy-leaved pelargoniums are not affected. It produce dark brown, fungal pustules on the underside of the leaves. They are arranged in concentric circles and there is a yellowing of the leaves above the pustules on the leaf top surface. As with any fungus it prefers a damp humid atmosphere to germinate and infect. It is easily controlled by spraying with fungicide like Scotts Rose Clear. The fungus can be present in the leaves for about two weeks before symptoms appear. Symptoms occur all year round indoors and outdoors when the temperature is above 7 degrees centigrade. In severe cases affected leaves turn yellow and drop off. This of course weakens the plant, but most plants survive the infection if sprayed with fungicide. If plants are heavily infected and weak, it may be best to destroy them and start again. This rust is believed to have originated in southern Africa and was first detected in the UK in 1965, but it has now spread around the whole world.
See also these other rusts Anemone, Antirrhinum, Bean, Bluebelle, Broad Bean, Cedar Quince, Chrysanthemum White, Fucshia, Gladiolus, Gooseberry, Hollyhock, Juniper Pear, Mahonia, Mint, Pear Juniper, Periwinkle, Plum, Potato Internal, Quince, Rhododendron, Rose, Rust, White.


The spores germinates and infect best when the temperature is between 7 to 25 degrees centigrade and conditions are humid and moist.
Infection can also spread via cuttings which are infected with the fungus as it has a long period, up to 2 weeks, when the plant tissue is infected but no symptoms are seen. Therefore it is best to quarantine new plants for that period for prevention purposes. Systemic fungicides are best for protection from this disease.
In the European Community the products permitted under organic regimes have little effect rusts. Fungicides containing myclobutanil (Bayer Garden Systhane Fungus Fighter and other formulations), penconazole (Westland Fungus Attack) and triticonazole (Scotts Fungus Clear Ultra) can be used to control rust, but care should be excercised when using these fungicides.
The fungus is encouraged by high humidity with a lack of air circulation. In greenhouses it is best to keep air circulation high and conditions on the drier side.
It overwinters on old plant materials so these should be burnt.
Spraying with a suitable fungicide is necessary and must be carried out several times.
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 as the rust needs a period of leaf wetness to germinate and infect.
Watering the soil in the dormant season with Jays fluid or Amarillotox should also help. In some Countries these products are not licensed for this use.
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.
Avoid over application of nitrogen, which produces soft growth which is more susceptible and ensure adequate potassium fertiliser.

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