Sometimes I cut open a bag that 2 cubic feet of mulch came in, and wrap that around what I want to spray, or what I want to protect.
A lot of spray tends to collect on the plastic and then run down into the soil, so it is better to spray a little, let it dry, then spray more, and repeat.
P.S. I also use those bags, or even 1-cubic-foot bags, to line a raised bed when the walls or corners would otherwise let the soil dry out too rapidly.
Once I even laid them UNDER a narrow, shallow raised bed that went on top of masses of roots from heather and rhododendron. I usually hate laying down plastic on the ground, but this seemed the only way to keep heather out of the 6" deep, 8" to 12" wide bed (its more like a container that sits on the ground, than a raised bed).
Well, surprise! Despite the shallow and narrow dimensions, that bed holds water better than any other bed I have, and turned out to be a MUCH better home for plants that like constant moisture (my summers are dry). (At the moment, yellow california poppies are thriving and pansies and doing OK. There are lobelia and snapdragons hidden by the poppies.
