This Neem Oil product is supposed to have very good anti fungal properties. The oil is extracted from the trees seeds using alcohol. If Black Spot is a recurrent problem I would look more closely at the soil these roses grow in to see what is missing, or not in balance, that allows this disease to be so prolific.

Oils can sometimes help with blackspot but they are much less effective than the products you have been using. You will also need frequent reapplications. And while roses growing in healthy soil will be more vigorous and better able to withstand blackspot infections, garden roses that are not resistant to this disease will become infected even in the most perfect of soil conditions. It has to do with a genetic lack of natural defenses. Hybridization of roses for flower form, production, color and so on has produced remarkable garden specimens, but they vary greatly in their ability to withstand BS infections. The best way to handle this disease long term is to grow varieties with high inherent resistance. Your local rose society is a good resource to find these out.

In recent years I have attended several rose lectures..by the local TV and Radio rose experts. Every single one has poo-pooed the using of harsh chemicals in our rose gardens. If you work to have healthy soil, stick with roses a bit more resistant to diseases in your zone..and if your roses get something you can use something organic..your roses can fight off disease

Absolutely make the soil you grow your roses in into a good, healthy soil which will grow strong and healthy plants that are better able to ward off plant diseases as well as insect pests.