Yellowing Rose Leaves

Yellowing Rose Leaves

Hi. I just joined this community, so forgive me if this question has been asked to death. I've got about 20 rose bushes, very hearty things — in fact the only plant in my garden that survived Katrina (I'm in New Orleans). They "woke up" around a month ago and did their first spring bloom thing. All looked healthy and happy. Now they all have the yellowing leaves (fungus, right?) and new shoots are drying up and falling off the branches. Two part question. 1) What can I do to stop the yellowing and get things healthy again? 2) Is there any way to prevent this from even beginning in the future? I'm constantly trimming them all back and giving them lots of attention. Last week I sprayed some soapy water on trouble spots to get rid of aphids. Could the soap have caused this? Could caterpillars which are everywhere in spring cause this? Is this just something that happens in the spring? I seem to recall having the same problem in April '05. It cleared itself up eventually, but, ugh! Thanks for your input.
Pictures of my garden

Pictures of my garden

Dahlias

Dahlias

Discoveries in the garden

Discoveries in the garden

yay i finally like my room!

yay i finally like my room!

A few pics and a few questions

A few pics and a few questions

beans beans

beans beans