Rose bush with black spots on leaves

Achasanai

Just wondering if this is a bad sign. The black spots are on nearly all the leaves lower down on the bush. What's odd is that the bush is doing better than ever before, and has lots of strong new growth and plenty of flowers. Should I be worried?

Sgt Pepper 64

Achasanai wrote: »

Just wondering if this is a bad sign. The black spots are on nearly all the leaves lower down on the bush. What's odd is that the bush is doing better than ever before, and has lots of strong new growth and plenty of flowers. Should I be worried?

Its a bad fungal disease. Burn or bin the leaves (dont compost them)

https://www.rhs.org.uk/advice/profile?pid=270


What is black spot?
Black spot is the most serious disease of roses. It is caused by a fungus, Diplocarpon rosae, which infects the leaves and greatly reduces plant vigour. Expect to see leaf markings from spring, which will persist as long as the leaves remain on the plant.

The fungus is genetically very diverse and new strains arise rapidly. Unfortunately, this means that the resistance bred into new varieties usually fails to last because new strains of the fungus arise to overcome it.

Symptoms
These are variable, depending on the rose variety and the strain of the fungus.

You may see the following symptoms:

Typically, a rapidly enlarging purplish or black patch appears on the upper leaf surface, with diffuse and radiating strands of the fungus sometimes just visible.
Leaf tissues may turn yellow around the spots and the leaf often drops, even though other parts are as yet unaffected
At other times, the yellow colour does not appear, but infected leaves still drop
Sometimes, the spots remain relatively small and the leaf does not drop
Small, black, scabby lesions may also appear on young stems
Badly affected plants can shed almost all their leaves and their vigour is greatly reduced. The symptoms are so severe that, anecdotally, the disease has been blamed for a decline in the popularity of roses in UK gardens in recent decades.

Control
Non-chemical control
Collect and destroy fallen leaves in the autumn, or bury under a layer of mulch. Prune out all stem lesions in spring before leaves appear. These actions will help delay the onset of the disease, but are of limited value because spores are bound to blow in on wind-blown rain from elsewhere.

Popular garden varieties of hybrid teas, floribundas, climbers and patio types are usually susceptible. Gardeners may gain a few years' respite by planting the newest varieties which claim resistance, but as discussed above, this usually does not last. Older species types are little affected.

Chemical control
The fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus), and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are labelled for the control of rose black spot.

Achasanai

Sgt Pepper 64 wrote: »

Its a bad fungal disease. Burn or bin the leaves (dont compost them)

Wow. A lot worse than I thought. I just assumed that because it was flowering so well, and had so many leaves, that it might be okay. Thanks for the reply!