Overview:

Tobacco budworms pupate over winter in the soil, about 2 to 6 inches deep.  Emerging adults mate in early summer.  Females lay eggs on flower buds.  After eggs hatch, larvae burrow into the flower bud and eat the developing flower. As the larvae grow, they move from spent flower to new flower, usually at dusk.  While geranium flowers may be entirely consumed, damage to petunia is usually less severe.  Still, the tattered petunia petals are unattractive and damaged flowers wilt sooner than usual. 

Caterpillars grow to about 1 1/2 inches before dropping to the soil and pupating.  In most of Utah there are probably 2 generations per summer.  In warmer climates with longer growing seasons, there may be four or five generations per summer.

 Tobacco budworm is resistant to many common insecticides, such as Sevin.  The organic insecticide B.t. (Bacillus thuriengiensis) can kill budworms feeding on petunia, since the flower buds can be covered with the spray.  Geranium buds are closed, so budworms eat very little B.t. as they feed inside the bud.  Synthetic pyrethrins are effective, but also kill many non-target insects, so should be used only as a last resort.