I am sorry for this delayed reply to your gardening question as we are transitioning to a new Q&A system. I hope this reply is not too late to be of help.
Black spot of roses is caused by a fungus. It is a major problem on roses across the country. The best way to manage it is to plant resistant varieties. There are several fungicides registered for use on roses that will control black spot, but regular spraying is required to maintain control on susceptible varieties.
Roses like lots of sun, well drained soil that is kept just moist and regular feeding. Apply a couple of tablespoons of a complete fertilizer around each bush every 3-4 weeks during the growing season and water it in well.
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