|The leaves on my roses all turn yellow and then brown, after that they fall off.|
|Disease is the most likely culprit, and it would be difficult to diagnose which disease without more information. For example, blackspot fungus causes black spots on the upper leaf surfaces, then yellowed leaves, finally defoliation. Rust is a fungal disease that causes powdery orange spots on the undersides of the leaves and eventual curling of the leaves. Viruses can cause mottled leaves, yellow circles on leaves and stunted plants.
As soon as you notice any of these fungus disease symptoms on your roses, remove and destroy any affected leaves and spray your plant with a compost tea. This can be made by putting a gallon of finished compost that contains some manure into a 5-gallon bucket and filling it with water. Leave the mixture in the shade for about 2 weeks, then filter the solution and spray. For best results, spray in the evening and repeat every 3 or 4 days.
Also, since many foliar diseases rely onhigh humidity for spread, water your plants in the morning and prune in the early spring to improve air circulation.
Good luck this year.