According to Fred :
I've heard lots of horror stories on the home owner destroying
valuable landscape when spraying for poison ivy (or any weed using
weed killer).

With a pinpoint sprayer and no cross-breeze, roundup is pretty
selective.

Best (for you) to remove it by hand. But if you must use chemicals,
then I'd recommend you use a brush or rag to wipe it on the suspect
leaves.

Aforesaid botanist said the best way to apply in tricky circumstances
(like right in the middle of desirable plants) is to wear a pair
of rubber gloves, then a pair of cotton gloves overtop. Stuff
the cotton gloves with some torn up cotton balls if you wish. Then,
simply dip your hand in the roundup solution, wrap your fingers around
the poison ivy, and slide your hand up the plant.

Poison ivy is really difficult to remove by hand, because it
spreads by long rootlets, at times quite deep in the dirt.

If you just pull it and leave any roots behind in the soil,
it'll grow back. Roundup will kill the roots.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.