I’d have to see screenshots from all your trees, passives, and uniques before I can look into this but I assume you have the Icarian Poison node, which is supposed to ramp up how quickly poison (or in this case armor shred) is applied.
There’s additionally a bug that is causing Aura of Decay to apply ailments (poison/armor shred) too quickly. This will be resolved in 0.7.7e.