Rose Care in Planters
I have 12 planters on my balcony with roses and each time I spray them with some kind of fungus or disease remedy, a few days after the lower leaves turn yellow and fall off. I do not understand why and I have took all the necessary measures to look after them properly. They are kept watered and are planted in part soil/part compost with rose food also. I have had them each 1 year. It makes absolutely no difference whether it is cold or hot at the time. This is happening and I do not know what to do. They give lovely blooms in the summer and autumn and at the moment on the top of the plant new shooots are coming through.
Sometimes it is the chemical being sprayed. The mix might be a bit off or if the product has been on the shelf a while it can alter a bit and cause such a reaction. I always water my rosebushes the night before I am going to apply any Pesticide. I found a great Earth Friendly fungicide called Green Cure. I have not had any black spot, powdery mildew or rust problems since I started using it. It is available on-line at a website called Planet Natural. They also have some great insecticide products and such. I would try using different sprays and see if that helps. Sometime though the lower leaves just turn yellow and fall off because it is the end of their usefulness to the rosebush and being lower they get shaded by the upper growth. It could be just their natural cycle that just so happens to time out with your spray applications.
Here are a couple links to articles for you too on this: