I realized I did not include the recipe for the spray that I use on the bud worm. Its easy to make, but you have to spray the plant frequently and thoroughly. But if you pay attention to your petunias and geraniums and spray them regularly, they repay you with lots of bright blooms.
Bud Worm Spray:
1 quart water
2 teaspoons organic SOAP - not detergent
1 teaspoon rubbing alcohol
I like to spray this on the plant in the evening and then, in the morning wash the plant off. Do not spray the plant in bright sunlight because you could burn the leaves. Also, you will notice a some flower petals will change color due to the soap.
Another treatment for budworm is any insecticide containing Bacillus thuringiensis/Bt (Thuricide, Dipel, etc.). BT is considered an organic control as well. It is also a good idea to look through the plant in the evening for the worm and hand pick them off. For more information on this you can go here: http://www.ext.colostate.edu/pubs/insect/05581.html
The bud worm eats the sexual parts of the flower, the stigma, and ovary.