Rose lovers are a breed onto themselves, because one cannot simply stick a rose plant into the ground, walk away, and expect perfect blooms year after year. They take work, but if you are a true rosarian, the results are worth the effort.
The rose’s susceptibility to black spot, which is a fungal disease caused by Diplocarpon rosae, is worse than mildew or rust because black spot frequently kills plants. It’s particularly deadly for non-resistant hybrid teas. Miniature roses are also highly susceptible.
Recognizing black spot early on is essential to its elimination. Look for small black spots with feathery edges, on the upper leaf surfaces; lower branches will be affected first. As the disease progresses, the spots will enlarge, become ringed with yellow, and- if the black spot is not stopped-the leaves will eventually turn entirely yellow and drop. Defoliation can cause the plant to die.
But have heart: a combination of prevention and fast action once the black spot is noted can save your plants.
- Do your research for your area, and plant resistant rose varieties.
- Placement is of upmost importance; plant far enough apart to allow for lots of circulation. Black spot fungus requires water to reproduce and grow.
- Plant your roses in full sun.
- Water in the morning to give your roses plenty of time to dry out.
- When you prune, immediately remove all diseased leaves and canes to the trash to prevent its spread to other plants.
- After pruning, use a dormant season horticultural oil spray.
A combination of 4 teaspoons of baking soda per gallon of water with a 1% solution of narrow-range horticultural oil is one way to manage black spot, along with powdery mildew. Avoid getting it on open blossoms. Neem oil may also prove effective. Don’t rule out preventive sprays of fungicides such as triforine or chlorothalonil.
Checking for black spot gives you the best excuse to closely examine, and while doing so, stop and smell your roses.