Do your roses grow in a shaded place?
Have you been pruning your roses recently?
Was it growing season pruning?
Does your roses show any sign of sickness or pest infestation?
Are the old flowers left on the plant?
Roses need full sun to grow healthy. If they don't receive at least 4-6 hours of direct sunlight daily, they will not bloom normally. Try to provide sunlight to your roses by thining shade casting trees and shrubs or transplant your roses in a sunnier place if thining is not possible.
If roses are excessively trimmed and pruned during the growing season, many flower buds may be removed so they will not bloom. You should prune roses during the growing season only to give them the shape you want or to remove dead or dying growth.
Improper dormant season pruning can lead to poor flowering. Don't prune roses below the bud union, because this will remove most flowering buds. Pruning during the dormant season should be done lightly, but if heavy pruning is necessary to wait until plants have bloomed in spring.
Check the symptoms of the disease that your roses are showing to find out exactly what is wrong with them and how to treat them. Many diseases and pests can be treated so don't write off your roses yet.
Roses will not produce many new flowers when old blooms stay on the plant. Roses will put energy into producing seeds on the old flowers so new flowers will grow rarer. Remove old flowers when they start to fade.
Your roses might have gone into their natural plant cycle. It is normal for roses to flower one time in late spring, and one time in late summer or early fall. They will not flower or will flower rarely if its not their time for blooming.
Schrock, D. 2004. Ortho home gardener's problem solver. Des Moines, Iowa: Meredith Books

Sreten null
Hi! I’m Sreten Filipović. I graduated from the Faculty of Agriculture at the University of Belgrade, with a master's degree in Environmental Protection in Agricultural Systems. I’ve worked as a researcher at Finland's Natural Resources Institute (LUKE) on a project aimed at adapting south-western Finland to drought episodes. I founded a consulting agency in the field of environment and agriculture to help farmers who want to implement the principles of sustainability on their farms. I’m also a founding member of the nonprofit organization Ecogenesis from Belgrade whose main goal is non-formal education on the environment and ecology. In my spare time, I like to write blog posts about sustainability, the environment, animal farming, horticulture, and plant protection. I’ve also published several science-fiction short stories.
You can find me on LinkedIn at https://www.linkedin.com/in/sreten-filipovi%C4%87-515aa5158/