I'm not sure what spray you are using but Bt (sold as Dipel, Thuricide, Biokill, Wormkill, etc.) works very nicely on budworm. It doesn't have much of a shelflife on the plant so you have to spray new buds every seven days. And the spray doesn't stain or harm the flowers.

Also fyi, the larvae don't live in the soil but the caterpillars will pupate there.

Joe

I have to spray BT once a week on my petunias, larkspur, pansies, dianthus, and especially ivy geraniums and Martha Washington pelargoniums. It's expensive (12.95), but a little 2 oz bottle lasts me all year. It does no damage to the flowers and it is non-toxic to animals and humans.

The moths (little light brown ones) will arrive every year in April and start laying their eggs on your plants. There is no way to beat them. They are everywhere.
Don't bother changing your soil, they'll just show up from somewhere else.

Good luck. Last season I posted a question: what is your worst garden nemesis? and mine was budworms.
Renee

BT works on the digestive system of the caterpillar and to be effective needs to be ingested when the worm is just beginning to feed. This is why the frequency of application is important. Al