Also make sure the Roundup you use is strong enough. I'd go with a 10%
solution to deal with poison ivy. Get the concentrate and apply it
with a tank sprayer, not the weak pre-mixed stuff, which is around 1%
and fine for general weeds. Also, you can get an additive that can
be used with any spray that make it stick to the leaves better. This
is important with poison ivy because the leaves are slick and oily, so
a lot of the spray tends to run off. That's one of the reasons you
need the Roundup to be strong. There are also other herbicides that
are labeled as brush killer that are effective as well.