We've used several pairs of the decoy mods my wife made, he usually cutting them from some fairly robust plastic and mounting them on bent metal coat hanger wires. We've done this for about 10 years, and we have watched butterflies fly in among the food and then turn and fly out apparently when they spotted the decoys. It's almost comical to watch but it certainly is a relief. The decoys usually, if marked with a good enough ink last four to five years and don't need to be moved around unless you actually move your brassicas around. Generally it looks like the decoys are probably an effective guard over 10 to 12 by 15 or so foot patches. You'd have to experiment with it to figure out how much space a pair of decoys would work for. But they certainly do seem to work well.
We've used several pairs of the decoy mods my wife made, he usually cutting them from some fairly robust plastic and mounting them on bent metal coat hanger wires. We've done this for about 10 years, and we have watched butterflies fly in among the food and then turn and fly out apparently when they spotted the decoys. It's almost comical to watch but it certainly is a relief. The decoys usually, if marked with a good enough ink last four to five years and don't need to be moved around unless you actually move your brassicas around. Generally it looks like the decoys are probably an effective guard over 10 to 12 by 15 or so foot patches. You'd have to experiment with it to figure out how much space a pair of decoys would work for. But they certainly do seem to work well.