A devastating insect pest of tobacco and cotton crops, the budworm (Helicoverpa virescens) also plagues the home garden. The ravenous caterpillars feed heavily on the buds and flowers of many garden favorites; vegetables, chrysanthemums, zinnias, gardenias, marigolds, nicotiana, petunias, roses and geranium. The damage occurs throughout the summer months but becomes the most noticeable during the late summer. Controlling the insects through handpicking or insecticide applications is often difficult.
Types of Insecticides
As the budworm matures, it becomes resistant to insecticide applications, especially pyrethroid-based insecticides. Insecticides containing permethrin, cyfluthrin, esfenvalerate or bifenthrin are all effective chemical insecticide control sprays. Consider using spinosad-containing broad spectrum insecticide sprays or powders in the vegetable garden because they offer a safer means of insect control on edibles. Spinosad insecticides do not kill beneficial garden insects. Bacillus thuringiensis insecticides are comprised of a naturally occurring bacterial disease that infects and kills budworms effectively.
Vegetable Garden Infestations
Budworms regularly infest garden vegetables like peas, squash, tomatoes, cabbage, peppers, cantaloupe and lettuce heads. The budworms will require prompt treatment with insecticides right after hatching because they will quickly enter the heads of lettuce and leafy vegetables. Once the caterpillars burrow deep in the protective foliage of the vegetable plant insecticides are often ineffective because the spray or powder does not reach the feeding budworm caterpillars.
Insecticides are the most effective when applied early in the season, when the larvae first hatch from the eggs or when the larva remains small, less than 1/4 inch in length. In order for Bacillus thuringiensis to be effective, the budworm must consume the insecticide. It works well when applied to the flower's surface so that the budworm will readily eat it, such as the flower of the petunia. It does not work well on plants that the caterpillar burrows into deeply before consuming, such as the geranium.
Effectiveness Time Frame
Spinosad insecticides provide protection for up to four weeks after application. Bacillus thuringiensis remains effective for only two days after application. Chemical based insecticides will need to be reapplied after several days to gain control. Each insecticide has its own effectiveness time frame. Apply chemical insecticides in the midafternoon for best results. The insecticides are available in spray form or a wettable powder solution.