Yes, this is rose black spot disease.
If it is not a large-scale planting, the following is recommended:
1. Prune yellow and withered branches to prevent further spread.
2. Spray Mr Ganick Organic Plant Acid RTU on the leaves and base of the plant once a week. If it’s the rainy season, spray twice a week.
3. Apply compost (approximately two handfuls) or Mr Ganick Bougainvillea & Rose Booster (about 15g) once a week.
For large-scale planting, it is recommended to use Mr Ganick BST (20g mixed with 20L of water) combined with an surfactant such as Mr Ganick Organic Silwet.
