Control (Rate of Decay) follows the usual rules for mass limits. It can increase the rate of decay by 10% x (level squared) or decrease it by 10% per level.

Common Modifiers [+40%] 
    Persistent [+40%] 
    Extended Duration (x3000) [+140%] 
    Based on Activation Roll [+5%] 
    Full Increase Only [-80%] 
    Reduced Duration (1/60) [-35%] 
        Applies to the ability to alter decay, not the Persistent effect 
    Magical [-10%] 
    Spell Components [-20%] 
        Must say "decay" in Latin 
        Must gesture with hands 
Level 1 [14] 
    Control (Rate of Organic Decomposition, Rare) 1 [14] 
Levels 2+ [+14/level] 
    Increase Control by 1 level [+10 base] 
Mass Levels 1+ [+9/level] 
    Add Control (Rate of Organic Decomposition, Rare) 1 [9] 
        Doesn't Increase Rate Control [-50%] 
        Further Mass Levels increase this by 1 level 
Rate Levels 1+ [+9/level] 
    Add Control (Rate of Organic Decomposition, Rare) 1 [9] 
        Doesn't Increase Mass Affected [-50%] 
        Further Rate Levels increase this by 1 level