How to recognise it
This fungal infection can appear similar to rose black spot, with rounded, red/brown patches appearing on the upper surfaces of leaves. However, unlike rose black spot, these patches can develop a grey/white mould growth on their underside in humid conditions. The leaves may wither and drop as a result of the infection.
Stems can also be affected, with long, darkened patches appearing.
Why it’s a problem
Can be unslightly, cause premature leaf fall and generally weaken the plant.
Where you are likely to find it
Mainly affects roses grown in glasshouses (ie for commercial purposes) but may occassionally be found on garden roses.
How to prevent it
Ensure that there is adequate air flow around and between the plants (this fungus thrives in humid conditions) and that good ventilation is provided for glasshouse roses, particularly overnight. Avoid overhead watering which can moisten the leaves making them susceptible to infection.
Maintain good hygiene around vulnerable plants, or areas where there has been an outbreak, particularly by removing and destroying any plant debris at the end of the season to remove any overwintering fungal spores.
Ensure you thoroughly clean any tools you have been using around plants which may have rose downy mildew, including your hands/gloves if you have been handling the plant.
How to get rid of it
Badly affected plants should be destroyed as they are likely to be weakened beyond the point of recovery and will only spread the disease.
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