I've always relied on viewing unit debuffs. Your debuffs are not the only ones that should be visible, its important to know how much damage / CC there is on target and for how long.
Additionally if you play somewhat correctly, there's almost no need to track your diseases unless its very specific timing like for Death Striking.
Spam plague strike for desecrates, slow people with Chain and use IT to balance your runes after plague striking. Pestilence vs melee classes on spare blood runes to generate RP and refresh diseases. You will automatically keep diseases up on target & around you, requires minimal effort and you can focus on other important details.