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Hollyhock Rust


Hollyhock Rust

Usually appear in

Spring to Autumn

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Caused By:-     The Fungus Puccinia malvacearum


This rust fungus is a major problem of hollyhocks. It is caused by the fungus Puccinia malvacearum which only attacks Hollyhocks and their relative the common Mallow(Malvs rotundifolia). This infection is one of the major reasons why this wonderful plant is not grown commercially any more and which has led to the declining popularity of this wonderful plant. Despite this debilitating disease the Hollyhock will continue to flower for years in favourable conditions until the plant finally succumbs and dies by other diseases. This fungus on Hollyhocks is characterised by the surface of the leaves developing many yellow spots which correspond with the underside of the leaves which are peppered with bright orange fungus pustules. These pustules may also form on the upper side of the leaves, on stems, and on green flower parts. The spores from these pustules are carried by splashing rain and air currents to other plants and parts of the plant to cause new infections. The fungus overwinters in infected plant debris and in the spring new leaves are infected by plant debris. The infected leaves become distorted and discoloured often with many holes which then die back. Hollyhock rust tends to become more severe as the summer progresses, killing most of the leaves on infected plants by the Autumn. Picture by Whitney Cranshaw, Colorado State University,
See also these other rusts Anemone, Antirrhinum, Bean, Broad Bean, Bluebelle, Cedar Quince, Chrysanthemum White, Fucshia, Gladiolus, Gooseberry, Juniper Pear, Mahonia, Mint, Pear Juniper, Pelargonium, Periwinkle, Plum, Potato Internal, Quince, Rhododendron, Rose, Rust, White.


It is important to break the disease cycle and remove infected leaves as soon as the fungus is seen. In winter cut all hollyhock stalks back to ground level after the worst of the frost has done its job and carefully collect all leaves and other plant debris and destroy them preferably by burning. Then watering the area with a soil sterilant like Jays Fluid or Amarillatox should help to control this fungus. In Spring and summer very two weeks from early spring onwards spray plants with a systemic fungicide.
For maximum protection begin fungicide treatments in early spring when the first leaves are expanding watering early in the day so the plant parts will dry quickly.
Try and avoid growing the common mallow, which are related to hollyhocks, in the vicinity.
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.
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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