Scale is a small sap sucking insect of about ½ cm, that covers itself in a dome shaped waxy armour. They come in a wide range of colours from white cottony tufts, through shades of grey to a dark red/black appearance and the covering can be hard or soft. But all look like your rose has tiny scales. Soft covered scale can be accompanied by a sooty mould from secreted honey dew.
Scale mostly appears on the stem of the plant but can be seen on the undersides of the leaves in bad infestations. They drill down into the soft tissue of the plant to feed.
If left, scale can breed fast and will spread to other plants. The sap loss will weaken or kill the plant if not treated.
The treatment will depend on the severity of the infestation.
For small problems: Scale can be gently scraped off with your fingernail or an old toothbrush. There are many home remedies but try a bit of rubbing alcohol dabbed directly onto the insect with a cotton tip.
For larger problems: Prune off any badly affected stems you can afford to loose and spray with an Agricultural Spray, either White Oil, Eco Oil or Neem to smother scale. As the incubation period on scales vary from one to three weeks, repeat the spray once a week over three weeks to catch the hatchlings. Always spray these in the cool of the day as Oil’s may cause burning to your plant if applied in full sun.
Please note that when the scale die, they stay attached to the plant but can be easily brushed off.