The main pests to affect roses are Aphids (green fly), rose scale ( a white cluster of bugs covering the rose stems) & two spotted spider mite. The best remedy for rose scale & spider mite is a Winter Oil spray applied during Winter when the rose has no leaves. The oil will smother the bugs & kill them.
After a few days you must scrape away this scale from the stems either with a firm toothbrush or small wire brush.The oil will also smother & kill any over wintering mite eggs left hiding on the undersides of these stems.
There are a number of sprays on the market that will help to eradicate these pests. Both are sucking insects that left unchecked will compromise the health of your rose.
Alternatively, encourage the local bird population into your garden & beneficial insects by planting flowers that will attract them.
The biggest bug bear on rose plants is Black Spot & Rust. As mentioned above, by spraying a fungicide, watering & feeding your roses regularly will help compact these diseases.
Just like humans, if your plants are well fed & watered they will be better armed to fend off infections & disease.