Black spot (blackspot) is one of the most common diseases of rose bushes; and, if left unchecked, it can cause quite a bit of damage to your rose garden.
Caused by the fungus Diplocarpon rosae, black spot begins just as its name suggests, with black spots showing up on the surface of the leaves.
As the spots grow larger, they become ringed with yellow, eventually causing the whole leaf to turn yellow and fall off. The stems may also have black or purplish spots. If not treated, black spot will leave your rose garden not only naked, but significantly weakened and unprepared for the next winter.
Like most fungal diseases, black spot thrives in wet, humid weather, usually when temperatures are in the mid-70s Fahrenheit. The spots produce spores which spread to other leaves and plants. The spores can survive the winter in fallen leaves and infected canes.
While black spot may seem relentless in your rose garden, it’s actually easy to manage with the right treatment and prevention strategies. Here’s how to control black spot in your garden.
How to Treat Black Spot
If you’ve noticed telltale black spots on your roses, you should:
Once the infected leaves and stems have been removed, treat your rose with a fungicide. Spray the entire plant, making sure to get the tops and bottoms of the leaves as well as the stems. You can use a chemical fungicide or any number of organic options such as:
- Lime Sulfur
- Neem Oil
- Potassium or Ammonium Bicarbonate
How to Prevent Black Spot
With these gardening habits in place, you can keep black spot at bay:
- Preventive Treatment: If black spot is a perennial problem in your yard, begin a preventive treatment with an organic, nontoxic, fungicidal spray (such as those on the list above), right before your roses sprout in spring. Continue treatment every couple of weeks to keep the fungus under control.
- Black Spot of Rose (University of Maine)
- Blackspot (Rose Magazine)
- How to Use Neem Oil in Your Garden (article)
- Protect Trees and Shrubs with Dormant Sprays (article)
- How to Control Powdery Mildew (article)
- How to Prune Roses (article)