word - A Halloween Riddle

My first's where you are when you aren't trick-or-treating
My next is the start of what kids will be eating
My third, when gigantic, might test your comport
My fourth starts the season where goblins cavort
My fifth is a note sung by sirens that lure you

My last's where you put the disguise that obscures you

My whole is a staple of magic primeval
For witches invoking the forces of evil

Answer

Thanks to Dr Xorile for seeing the final solution from my first attempt and GentlePurpleRain for the last fix in formatting:

My first's where you are when you aren't trick-or-treating

IN, because when you're not out trick-or-treating, you're in.

My next is the start of what kids will be eating

C, the "start" of candy.

My third, when gigantic, might test your comport

ANT, as in a comport-testing gigantic ant.

My fourth starts the season where goblins cavort

A, the "start" of autumn.

My fifth is a note sung by sirens that lure you

TI, one of the notes do, re mi, fa so, la ti, do

My last's where you put the disguise that obscures you

ON, because you put the disguise on to obscure your identity.

My whole is a staple of magic primeval

For witches invoking the forces of evil

INCANTATION