Both of these require that trails are overgrown and neglected. If you stick to mainstream trails with a lot of traffic and regular (probably volunteer) work to trim them, this won't be an issue because you won't be touching any plants while riding the trail.

I'm in Kansas, and I have gotten ticks from trails where tall grass brushes your legs when you're in the middle of the trail. If it's trimmed back, you won't be in that grass.