I've seen lots of scarecrows in my gardening life, and sometimes I think the scarecrows are more for us humans than they are to actually scare crows away. The coolest scarecrow I've seen was named Esmerelda and she had a really neat hand painted gourd head, mardi-gras beads, boobs, cool dress, and I don't know if she scared any crows away but she was way cool. She lived in a blueberry patch.
I've just planted the first planting of sweet corn, and as soon as those kernels sprout and head skyward the crows start plucking. Today I was working in the tomato patch (installing drip tape, yet another blog story) and I heard the crows squawking. I know the corn hasn't come up yet, but that was my signal to install the scarecrows.
When I first started growing corn here, it was the first time I had actually grown corn (about 3 years ago). I never really had enough land to grow corn, since it takes quite a bit of space to do well.
When the corn started sprouting that first year, my neighbor told me he had seen crows eating the sprouts. I panicked, and immediately thought "oh my gosh, I don't have clothes for a scarecrow, or a hat, and what kind of head do I put on it?" (lol) He told me the best scarecrow was to simply tie a black garbage bag on a pole and stick it in the ground in the corn patch. The crows think it's a dead crow on a stick so they don't come near.
I've got these neat plastic fence posts that I've used for everything from flower bed surrounds, chicken lots, dog lots, flower bed protection to tomato supports.....blah, blah, but every spring, several of them don garbage bags and keep the crows away until the corn gets too big for the crows to be interested in messing with it. Trust me, it works here! I put them about 30' on center around the corn patch. Cheap and reliable.