In an effort to desensitize to plastic bags and other things I used a plastic, push in the ground type fence post. Like this:
And tied new things to it for the horses to investigate. I put the post in the middle of the pen and attached the "new things" to the post, the horse could then investigate it at their own pace.
I tied plastic bags that would blow in the wind, black garbage bags, sleigh bells, a piece of an old tarp, a hula hoop with the rattle beads, milk jugs, 2 ltr pop bottles, even some pop cans. Anything you want them to get familiar with that won't hurt them.
I would leave the "New item" on my "introduction stick" for a few days and let the horses get used to it. The items couldn't chase them, the horses had plenty of room to get away from it, and more than anything, it gave them something to think about. The more items I put on the post the faster they got used to them...the stick turned from the scary post to the discovery stick. I LOVE letting a horse figure out anything that they can possibly learn on their own
...( I mean if they can learn to be ok with it on their own that's better IMO than forcing something on them, not all principles apply here)
Once they were OK with the object, I'd rub it on them, by the time we got to that step they didn't care much anymore.