Roses Down Under

With the problems I have been having I decided to do some research onthe rust which is found on roses. The species Phragmidium (rst) has a number of different types, each of which is restricted to one or a few host species. For example P. rubi-idea is only found on raspberries, P. violaceium on cultivated blackberries and loganberries, and P. tuberaculatum is the particular type of rust which infects roses. The rust on hollyhocks is different again, Puccinia malvacearum, and fromwhat i read everywhere rust does not jump from species to species, so I don't have to worry that the rust on my hollyhocks is infecting the roses.

Rose rust is a fungus which first appears as small orange or rust coloured spots on the leaves and will become more prominent as the infection advances. At this stage there will also be rust spots on some of the stems too. Some publications say that rust will be more likely to be foundwhen the humidity levels are high and the temperatures are warm to very warm. Certainly when conditions are favourable rust can appear quite early in spring, first showing as small orange spots on the top of the leaves. The infection then spreads quite quickly and there will be many small raised orange spots on the underside of the leaves. If this is left and the weather is giving the best incubation conditions some roses will have all the lower leaves infected.

As the season and the disease prgress the orange spores change to small black pustules or raised areas which contain overwintering teliospores. Leaves which are badly infected will fall off the bush. Some rose bushes affected by rose rust will completely defoliate, and this can threaten the life of the bush.

When looking this up on various websites there are many differing view as to how bad a rust infection can be, from 'most infections are light enough not to require control' to 'if left untreated rust spots on roses will eventuially kill the plant'.

How do you treat it? Spraying with a fungicide of some sort is the recommended treatment. Sprays containing sulphur or copper are the ones mentioned most often. But just as important as spraying is good garden hygiene, picking up all infected leaves as they fall and in bad cases pruning out infected stems and destroying them.

Some cultivars are definitely more pront to getting rust than others. I have a few in my garden which are my indicator plants, and some of them are so badly infected this season they will probably be given a ride to the bonfire heap in the late autumn! But for some reason this year plants which have never had rust before are quite badly infected. It must be the weather conditions which are causing it.

I normally don't spray my roses at all, but this summer I think I will have to get out my sprayer and douse the worst affected roses with a copper spray. I know that will mean most of the affrected foliage will drop, but it may stop the infection from spreading even more. And one day when I feel so inclined, I will go out with a large plastic bag, pick up all the dropped leaves, and put them in the rubbish bin.