Rust is a fungus
Rust is another disease which is a lot more prevalent in our climate. But the news is not all bad. In a large proportion of cases, this disease arrives instead of, rather than as well as! The disease it pretty much replaces, is powdery mildew – a disfiguring mouldy white fungus which only occurs on a very few, extremely prone cultivars, none of which, in our experience are David Austins. Yippee.
So if you read that a certain rose is prone to mildew, 99% chance is, it won’t get mildew in our climate at all (powdery mildew, that is). Unfortunately it will most probably get rust (which is, of course, worse than mildew). Rust, particularly well named, appears as “rusty” spots under the leaves, a few at first, and then, if the plant is particularly prone, lots, that cover half the leaf, start to appear on the upper surface as yellow spots, and eventually cause the leaf to die and drop off.
Because of the texture of the spots, quite powdery and easy to rub off, the spores seem to spread more easily and infect neighbouring plants. In light of this, removal of infected leaves is even more important than with other diseases, alongside the inevitable spraying.
Roses badly prone to rust can often lack vigour, due to the continuous battle to produce new leaves. Not many David Austin’s fall into this category, but the ones that do must be sprayed very regularly or left in the shop.
The good news is that most of the broad spectrum sprays prevent rust. and some are systemic.
One other thing to note about rust is that, like spider mites, this is not a rose specific phenomenon. Some annuals and perennials ,for instance antirrhinums and hollyhocks, need spraying alongside your roses to keep the enemy at bay. Another common plant that shares hosting that we have observed, is Kikuyu grass. Unfortunately this is a “weed” that does extremely well in our district, but as it is a hideous nuisance in or near the gardens, this is a good reason to get your poison out and “round-it up”.