[Teabag]

would really fresh manure burn down into the roots of some of the perrenial weeds on my plot,i can get loads of the stuff and thought i might try it

[blackbob]

probs easier to use roundup
i think your on to a loser with that plan,heat rises so it aint gunna get the roots i'm afraid.
get all ya free muck and stack it the more the merrier

[Trillium]

I agree with blackbob. Some perennial tap roots can go down 4 ft easily and fresh manure would never reach that far. But a systemic like glyphosphate would, though it sometimes might take several tries.

[Tigerhair]

Cover it with something - carpet, cardboard (worked for me) or plastic (black) - keep your poo for another day when it's rotted.

[Diggerpete]

Best way's to dig them up if you can.