Hi nagendra,
Here are a few organic pesticides and tips for rose cultivation.
Bordeaux mix helps to prevent fungal diseases, including black spot and powdery mildew. If it’s a problem every year, do a preventative spray right after spring pruning, but before the leaves open.
•Potassium bicarbonate fungicides can be used on mildew during growing season, in extremely humid areas. It tends to be safer than the homemade solutions with baking soda (sodium bicarbonate).
• Severe fungus infections can be treated with copper or sulfur fungicides.
Consider companion planting to deter bugs. Alliums to repel nematodes, nasturtiums to trap aphids, alyssum, geranium, rosemary and thyme to attract beneficial insects.
Regards
Ashwini S