Ok...by scabs do you mean something physically on the leaves (not bugs) or do you mean little red bugs crawling around.
If it's "scabs" could be rust fungus. Is the plant kept moist or somewhere that is VERY humids. Rust fungus is naturally on/in all plants, but comes out when it is humid. Best thing would to be remove the most infected leaves. If you want a natural remedy, that will be hard. First of all, put the plant somewhere dryer. Second, mix cinnamon powder in water until disolved into a thick paste, and paint it on the plant with a brush. You won't be able to put cinnamon into a spray bottle, as it doesn't dissolve, so it will just clog it up (so don't try). I find as an anti-fungal the past works the best. Then let the past dry and don't peel it off. Other alternatives would be sulfur power (naturally occuring but poisonous in large doses, so keep off your skin etc). Take plant to somewhere outside and dust it with sulphur powder. Keep it somewhere that animals/humans won't be near for several weeks, then wash it off and repeat if necessary.
If it's little red bugs (you will see little bugs moving and some webs) they are called spider mites. That means the area the plant is in is too dry. Move it somewhere more humid and spray with a superfind horticultural oil, insecticidal soap, a mix of soap and water (non-antibacterial), or neem oil. You need something that will smother the bugs and kill them and larvae.
Hope this helps.
Prevent a litter
Fix your critter