I have used Tabasco sauce diluted 1:10 with water spray plants. It is somewhat helpful, just have to reapply every few days or after a rain. Sometime ago I read a very inexpensive way to keep them from bird feeders. Not pretty, but inexpensive and the most effective I have found. I used an empty birdseed bag (40 lbs), opened a the bottom large enough to get over the pole between the bird feeder and the ground. Tie in place to create a hood on the pole. Squirrels crawl up the pole and end up inside the bag unable to reach the bird feeder. I have been using this all summer and have lost far less bird seed than normal. Unfortunately it does not work for grackles when they are around.