Downy Mildew and Botrytis
Downy mildew and botrytis both become more important when conditions are cool, moist, humid, or crowded. They can be confused with other rose problems from a single photo.
Downy mildew signs
- Angular purple, red, or brown leaf patches, often limited by veins.
- Yellowing and quick leaf drop.
- Pale growth on leaf undersides may appear in humid conditions.
- Can be more sudden and severe than black spot.
Botrytis signs
- Spotted petals and buds that fail to open.
- Grey-brown fuzzy mould on decaying petals, buds, or stems.
- Problems during cool wet spring or autumn weather, or in very humid sheltered sites.
Controls
- Increase air circulation by spacing and pruning.
- Avoid irrigation that leaves flowers and foliage wet for long periods.
- Remove and dispose of infected flowers, buds, leaves, and cane material.
- Reduce dense groundcover around roses where humidity stays high.
- For downy mildew, environmental management is often more realistic than rescue spraying in home gardens.
Direct treatment notes
- Fungicide labels for downy mildew and botrytis are more specific than general rose disease sprays. Do not assume a black spot product controls downy mildew.
- Check local extension, RHS, HSE, or EU/member-state authorisations before product use.
- Severe suspected downy mildew, nursery-stock issues, or repeated rapid defoliation should be escalated to a diagnostic service.
Use controls lawfully: Current local product label/register wins for any pesticide, fertiliser, or soil amendment use.
Sources
Discussion log
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