Answer: What pests! You might try setting a protective barrier of wire mesh over the plants, you can string clear monofilament fish line 6-8" above each row, and a couple down either side of the plot to keep the crows from landing in the patch so they'll encounter the line when they try to land, and get confused by the unseen obstruction, or possibly a floating row cover would exclude them.
Continuous flagging is the most traditional way to keep birds from crops such as corn. Stakes are placed 15 to 20 feet apart all around the corn patch and a long flag of cloth is attached to the top. The flag can be tied directly or tied first to a string and the string attached to the stake (gives more play iin the wind). Set up the stakes before the corn is attractive to the crows. Another method, although more frequently used for ripening fruit trees or small fruits, is bird netting.
Noise makers like a radio (got any neighbors who might be bothered?), mylar or metallic flash tape and balloons (the reflection bothers the birds), strings down the row with streamers of flagging tape, all of which have been used with varying degrees of success. Varying your scare tactics works best, as it keeps pests from getting used to them.
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