Growing roses organic starts with the soil for roses.
So organic care for the soil in which they grow is a must if you want a healthy rose garden.
Most of us do not have perfect garden soil. But good soil is the basis of all gardening, and an absolute requirement for good organic gardening.
Constant mulching with organic materials
Roses likes richly organic soil. Since they grow and bloom over a long season, roses need lots of organic rose food
They seem to prefer clay based soils that hold nutrients longer, and give firm support to their shallow feeder root systems.
So if your soil is very sandy, you need to add lots of organic soil amendments, maybe as much as 75%, and really work it in well.
Also adding a 2-3 inch layer of organic mulch every month during the season will really help, especially if the weather is hot.
Try the baking sode solution for general fungus disease.
Here is the recipe: 1 tablespoon baking soda, and one tablespoon light-weight horticultural oil to 1 gallon of water. Mixed thoroughly.
Apply late evening, or very early in the morning, a day after a thorough watering.
The foilage needs to be dry so direct sun won't burn it.
If you use this mild rose spray for fungus diseases, make sure you do so on a regular basis. For example every week.
Haphazard spraying applications don't seem to produce reliable results.