Recognising and treating fungal infections and viral diseases on roses

The well-known diseases of roses are mostly fungal diseases, which like to spread especially in larger rose plantings.

Warm, humid spells of weather also encourage them.

In general, a well-ventilated site is probably the best protection against an infestation.

If an infestation does occur, the fallen leaves should be collected as soon as they have dropped from the plant and disposed of (not in the compost...).

Spores sometimes lurk in them for years, waiting for the next chance to infect!

Anyone who wants to enjoy healthy roses for a long time and wants to prevent rose diseases can pay attention to a number of things over the years when planning and caring for their roses. Besides the right site, an adequate supply of nutrients (proper fertilising) is decisive for later infestation with fungal diseases.

​​Roses love deep as well as loose soils with a high humus content and sunny positions. In heavy soils, the planting area should be backfilled "two spades deep" with sand and compost. This gives the rose a loose soil with important nutrients.

The ventilation of the site also plays a role. A well-ventilated site speeds up the drying of the foliage after rainfall and the morning moisture ('dew'). Fungal diseases are strongly promoted by prolonged moisture.

Another point is fertilising. Nitrogen-rich fertilisers after the first flowering push the plants into vigorous growth, but make them more susceptible to fungal diseases. Less is often more here.

Powdery mildew is recognised by a reddish-violet discolouration at first, which in the course of time turns into a white, floury coating on the foliage.

Affected parts of the plant should be removed by cutting back into healthy wood. Alternatively, systemic fungicides are available from specialist retailers, which can also be used preventively every 10-14 days.

Downy mildew shows itself as red-violet patches on the leaves at first, which later turn grey-black.

A heavy infestation leads, as with powdery mildew, to premature leaf loss. Downy mildew can generally only be treated chemically.

Recognisable by round spots with a light centre that later falls out. Treatment as for mildew.

Appearing already at the start of the season, but often in July and August, rose rust quickly and reliably leads to massive leaf loss. Leaves infested with rose rust have orange-red to blackish-brown fungal spores on the undersides of the leaves.

With a light infestation it is enough to cut off the leaves and dispose of them safely; a heavier infestation requires the use of an approved fungicide.

Black spot also leads to premature leaf loss on the affected plants. Black spots of varying size on the leaves are a sign of infestation.

Treatment is the same as for rose rust. Effective products are available for both diseases.

Since this is a virus, it can hardly be controlled. To prevent the epidemic from 'spreading', plants that show yellowish ring spots, line patterns or vein clearing on the foliage should be destroyed.

In any case, ask your gardener (or in our forum, with a photo) in order to identify the disease with certainty before taking this rather drastic step. Rose mosaic is mainly transmitted during grafting and should now only very rarely be encountered!

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• Help is given here for a rose bush that lets its leaves, heads or even everything droop
• Here you get advice on black spots on the rose leaves