Caterpillars come back to eat petunias every year
I live in NYC and am a terrace gardener. I love to grow petunias, particularly trailing ones as they can be seen from the street from my 4th floor terrace. My petunias for years have been plagued by caterpillar damage. As many others have suggested on this forum, I use BT (Bacillus thuringiensis), which works very well, but the caterpillars always come back, every season, with the damage usually apparently beginning in early July. I have to spray the BT the rest of the summer, and it is a hassle, not to mention the awful smell. Not sure what type of caterpillar they are; they are green and, before I learned about BT, they used to get pretty big and fat. If I spray a lot, they must die off, but are seemingly continually replaced by new ones, so the ones I see these are generally smaller and skinnier.
I've talked to lots of people here and very few of those who grow petunias have this problem. I see healthy petunias all over the city in window boxes and I find it VERY hard to believe all these city folks are diligently spraying their flowers! So I can only conclude that this is not a widespread problem that everyone has; however, I wonder if, once you get them, these annoying little guys lay eggs that can survive the winter and just keep coming back. I once tried changing out all of the soil, but it didn't help (it's possible I wasn't diligent enough in getting rid of all the old soil).
This year, I did not grow petunias. I have only now, almost mid-August, begun to see caterpillar damage, on geraniums, and it is very, very minor. I think geraniums are not really their thing; sticky petunias are like fuel for them. So I am pleased but would love to get back to growing petunias next summer.
Does this theory make any sense at all? Can the eggs survive the winter? Multiple winters? How do I get rid of this problem for good? The fact that so many people are not experiencing this encourages me that is it is possible.
Thanks for any help you can provide!