In message . com,
tom&barbara writes
Hiya folks,

Hope you are all enjoying the glorious weather! Have been lurking for
the last few weeks as have had no questions and have been unable to
answer anyone elses. Well all that is about to change I'm afraid.

I have some hollyhocks in the garden, only about six of them. I have
noticed that the leaves have some sort of disease, there are masses of
bumps on the underside of the leaves and I mean absolutely loads. The
leaves are literally covered with what looks like loads of eggs,
although I don't think they are eggs, they are also an orange colour.
The plants don't seem to be getting very tall but they do have buds on
which look fairly healthy. Does anyone have any ideas or know what
this is? Thank you in advance.

Hollyhock Rust (Puccinia malvacearum), also known as Mallow Rust or
Malva Rust. This is a South American fungus which has spread more or
less worldwide, and affects a variety of plants in the mallow family -
particular Hollyhocks, Common Mallow (and some of its weedy relatives)
and Musk Mallow.

It's claimed that Antwerp Hollyhocks (Ficifolia Group) are relatively
resistant. I suspect that the bloodlines of Alcea rosea are so
intertwined that you can't rely on this. It's also claimed that Alcea
rugosa is resistant as well. Herbaceous Lavateras (Lavatera thuringiaca
and cvs) are pretty much resistant and have a similar habit, but not the
range and intensity of colour.
--
Stewart Robert Hinsley
http://www.malvaceae.info/