A time to start cutting these down. It will be to remove dead, damaged and diseased wood. In high winds, it ensures minimal damage to branches if it can move through the Rose. It will improve next years flowering – if there are no pointless branches the energy can move through to where it is needed most. Some leave until spring to do only once. You can return to them in spring if uneven growth starts to bolt. This job should really be done from september in preparation for winter, if not then do leave till spring. It will acclimistise for winter but hard pruning in “baltic” conditions will weaken it.
There is some disparity in the the care of Roses. Some say time-intensive, some argue too much method. Roses are relatively straightforward if you follow a few steps, if anything disease is more likely to thwart it than you.
Prune to a leaf node/bud to avoid dieback. This is an improper cut to the stem which simply goes brown and remains inert. It stores no energy so remove. Dieback however, can be a result of infected soil from previous planting harbouring grey mould and canker. Cutting back in a correct manner highly reduces this risk.
Remove any crossing branches to ensure full circulation and stems do not touch. This is general practice to avoid diseases spreading, cross contaminations. It is also reshaping the Rose so it retains its desired habit.
Cut back spent growth, straggly or unwanted. Look for central stem and 3/4 outward stems (dependent on how big), cut back shoots to 3/4 leaf nodes from the bottom. This should be maybe a third of its height. You can use your discretion for aesthetics. It depends how brave but it will be absolutely fine.
Roses seem susceptible to a number of diseases and pests although some varieties more than others. Varieties are crossed for resistance but as the cross species adapts to fight off the disease, the disease also adapts to survive.
Rust is a fungal disease, it affects the leaves – they will fall before they should. The plants overall performance is affected, in extreme cases can kill a Rose.
Powdery Mildew is a debilitating condition for a Rose. It is easily avoidable. It is usually to high conditions of humidity and lack of air circulation. Spores will infect the plant and impede its performance. Grey mould is pretty much the same thing.
Black spot, a fungal infection that blackens the leaves. Varieties are created to overcome infection but as discoveries are made, Black spot adapts to survive. Older varieties seem to be safer for some reason. Cut out the infected area and remove diseased leaves in autumn.