Risk vs. reward/threat assessment :p

I would pop on a tall, sturdy pair of boots and go for it!

You should definitely go for the shot! Why the heck not? Like the others said - just make sure you wear boots and don't snag your dress on anything

I would do the shot, but wear leggings/boats so that you are better protected.

Tick activity is relatively low August/September, but starts up right before winter unfortunately. However, with the leggings, you'll notice them before they get to your back and your dress should contrast them too, just have your bridal party check it over once the shot is done. You'll be dealing with adults vs. larvae which are usually bigger/easier to spot as well. Have someone carry some tweezers just in case!

I would totally do it. or at least get just far enough into that the photographer can make it appear/take the shot you are all the way in. maybe for that shot. make sure you wearing rubber boots or something. and get your girls to fluff/brush out your dress after.

I hope to get this sort of shot for my wedding, but doubt it'll be possible (unless we can find some awesome tall grasses that weren't crushed by all the Alberta snow!).

I say get the shot - Peak season for ticks in Atlantic Canada is May/June and October/November. The chances of coming into contact with a tick are relatively low in September. One thought is to wear a pair of leggings and boots while getting the pictures - you won't see them in the shot, but they will protect your legs enough to help prevent latching on, and even if they do, you'll be able to see them right away.