I got a few very old rose-bushes in my garden. As in most years,the
roses had bloomed gorgeously, now for the second time.
What has been worrying me for a few weeks now is that the bushes have
been massively losing their lower leaves; they turn a dirty brown and
fall off. I couldn't detect any bugs or mildew. What other desease
could have befallen them?
Thanks for advice.

Yoyo