How do I prevent and treat blackspot on roses?Updated a month ago

Black spot is one of the most frustrating fungal diseases for rose growers, but it can be managed with a proactive approach. Prevention is key. The best way to handle black spot is to prevent it in the first place. Felicia recommends choosing disease-resistant varieties whenever possible, planting in full sun to allow the leaves to dry quickly after rain or morning dew, pruning for airflow—good air circulation helps prevent fungal spores from thriving and watering at the base and avoid overhead watering.

If you start noticing black spot, here's how to get ahead of it:

• Remove infected leaves promptly. Pick them off and dispose of them (don't compost).
• Apply an organic or synthetic fungicide. I personally like rotating between products to prevent resistance. Options include:
  • Organic: Neem oil, copper-based sprays or a baking soda solution (1 tsp baking soda + a drop of dish soap in a quart of water).
  • Synthetic: Products containing myclobutanil or tebuconazole work well for serious cases.
• Spray regularly. If black spot is active, spray every 7–10 days, especially after rain.

Should You Completely Defoliate the Rose?

No, you don't need to completely strip the bush of all its leaves—that can stress the plant and slow down recovery. Just remove the worst-affected leaves and continue treating. Remove no more that 50% of the total volume of leaves from the plant. If it's late in the season and the plant is already struggling, you can let it go dormant and do a hard prune in early spring.

Do You Need to Replace the Mulch?

Yes, it's a good idea to refresh the mulch around your roses if black spot has been a persistent issue. The fungal spores can overwinter in old leaves and debris, so rake up and dispose of fallen leaves and replace old mulch with a fresh layer to help block spores from splashing back up onto the plant.

If you stay consistent with these steps, your roses will recover and have less disease going forward!