I have been noticing that my canna leaves (all rolled) are turning brownish with what appears to be eggs. They also have some holes in them. I opened up the rolled up leaf yesterday to find a green caterpillar. It seems to have affected more than half the leaf. I removed the half of the leaf along with the nasty creature. A new leaf had also comeup and when I checked that, it has some holes in it too . What can I do to prevent this? My cannas are in huge barrels and are just sprouting. I am so frustrated.