Symphilids (Hanseniella ivorensis)
Small pests which look like tiny 1-2 millimeter, cream or white colored centipedes.
But unlike centipedes (harmless to plants), they destroy small roots and burrow into the larger ones, where corky patches indicate areas that these pests have gnawed.
Your plant will begin to show signs of necrosis and leaves will start to die off.
It does not take long for the whole plant to become affected with no recovery from the damage.
Symphilids are not normally found in sterilized potting mixtures. They most commonly occur when using manure or compost based mixtures which have not been sterilized.
If infestation is suspected here's a way to determine if you have them:
When you water your plant they will rise to the surface of the soil and you can plainly see them crawling on the top of the soil.
If you do find an infestation, than the soil will need to be treated with an appropriate pesticide.
From personal experience I have used Fungus Gnat Killer ( "B.T." a non chemical / biological control) in the powdered form. Sprinkle it on the surface of the soil and water it in. One application will kill most of the living larvae, but to be thorough, it is better to repeat a second application 7 days later to catch the breeding cycle.