Answer #1 · Maple Tree's Answer · Hi M-Overhead watering or a lot of rain can cause fungal diseases. With all the rain you have received most likely the foliage is not drying quickly early in the day. If days have been cloudy this makes it even harder for any moisture on the leaves to dry. Roses are very susceptible to Black Spot fungal disease when moisture is allowed to stay on the foliage for any period of time. Black spot disease typically begins as black spots on the foliage and are most prevalent on upper leaf surfaces. Leaves eventually begin to yellow around the spots, then become all yellow and fall off. The spots may also appear on rose canes, first being purple and then turning black. Roses are also susceptible to Powdery Mildew but this fungal disease is usually caused by warm daytime temperatures with cool moist or humid nights. With Black Spot, any infected foliage or stems should be pruned out and any fallen leaves should be raked up and discarded in the trash. Do not add any infected stems and foliage to a compost pile. These fungal diseases should be treated along with pruning out infected parts of the roses. I noted a link below to an article that will help you with the treatment of these diseases. The article will give you some products and application tips on the treatment of your roses. Just click on the link to go directly to the article.

http://www.gardenality.com/Articles/74/Problems-and-Solutions/Diseases-and-Fungus/Disease-Control-for-Roses/default.html

I uploaded a few pictures of Black Spot and Powdery Mildwew on rose leaves for you to see. Let me know if these resemble what you are seeing on your roses.

Please ask if you have any other questions.

John)