Budworms

Budworms - they're not just the bane of marijuana growers!

Budworms destroy flowers, buds, and leaves, and there are several types. All of them are the larval stage of certain moths. They are called budworms because they burrow into the flower buds of tobacco, marijuana, spruce, cotton, petunia, nicotiana, and geranium. After those resources have been exhausted, budworms start feeding on many other nearby flowers, such as roses, snapdragons, angelonia, and penstemon.

Tobacco budworm (USDA) Public Domain

Budworm lifecycle

The budworm begins its life cycle as an egg. These spherical, flattened eggs are laid singly, usually on buds or leaves. The newly emerged larvae may be colored olive green to reddish brown, with longitudinal stripes and several rows of spines along the back. Depending upon the specific species of budworm and the food they are eating, the color may change to match the host food, making them difficult to see. Budworm larva go through several instars. After gorging on your flower buds and other plant parts for a month or so, adult caterpillars drop to the ground where they burrow down 4 to 6 inches and pupate into moths. There are generally two or three generations each year, in spring and summer. Each species has distinct descriptions and host foods. Two of the most common budworm pests:

• Tobacco budworms (Helicoverpa virescens) - Cream colored or grayish-brown moths, 1/2 inch wide, with a wingspan of approximately 1-1/2 inches; larva feed on many annual flowers.
• Spruce budworms (Choristoneura fumiferana) - Brown moths with 2 dark half-circle spots on either side of the wings; larva feed on many conifer trees.

Damage caused by budworms

Tiny budworm larvae burrow into small flower buds, where they feed and grow. As they become larger, budworm emerge from inside the ruined flower buds to feed on nearby mature flowers and leaves.

How to control budworms

Very often, budworm damage isn’t seen until flowers are open or the bud is destroyed. Monitoring buds regularly is critical for control. Check buds and flowers for small holes. Holes in buds will average 1/16 inch in diameter, while leaf and flower holes tend to be 1/8 inch. Handpick any visible caterpillars, which are normally most active during the evening and hide near the base of the plants during daylight hours. Chemical insecticides have not been found effective. Luckily, treatments containing Bacillus thuringiensis/Bt are effective when sprayed early and regularly enough. Rototilling or installing landscape cloth over affected areas during the fall may disrupt the budworm lifecycle.