Howdy Nick,

I work for The Home Depot and I have years of experience with roses and other plants.

From what you've stated, it sounds like you have a mixture of blight or black spot and perhaps a pest has burrowed into the rose bush. Burrowing bugs are usually harder to fix that the plant is worth.

The blight is from a disease in the soil that affects the plants branches and leaves. The black spot is also a fungus
that causes problems on roses.

Remember, plants can have more than one disease at a time.

Lastly, if it is an old rose, the cracking bark will provide a soft point of entry for evil boring bugs such as: raspberry cane borer, rose stem sawfly,and rose stem girdlers.

If you decide you would like to treat the blackspot here are my methods.

First I would trim off all the affected leaves/branches and dispose of immediately. Make sure you dispose of the leaves on the ground as well.
Next I would recommend a solution made with baking soda. Dissolve 1 teaspoon baking soda in a quart of water, add a few drops of liquid soap to the mix to help it cling better to the foliage, spray infected plants thoroughly.

I hope this fixes your problem,

Yours Respectfully,

Coach Dave

It sounds like aphids, a major problem with roses. Try the baking soda route or a more intense spray that you can find at a garden center.