By Alex116
Nairnshire,
United Kingdom 
further to my question on my stag's horn
(a) yes the leaves are still green but not growing
(b) buds have dried out and rub to dust
(c) appears to be a lack of sap in wood
(d) finally since the severe winter snows there has been
abit of a drought and high winds
8 May, 2011
Sounds like it's drying/dried out Alex. Have you watered it at all? Established trees don't usually need to be watered once they've been in a year or two, though.
Have you done the bark test? You scrape a little bit of the bark away and see if it's green and moist underneath, or brown and dead. If the top growth is dead, I'd cut it back. Sumacs are legendary for suckering from the roots, so it's extremely likely to regrow from the base, even if the top is dead.
8 May, 2011