Tobacco Budworm Really Bites

Source from:  By Maggie Wolf Special to The Tribune  07/04/2006

Pests destroy budding flowers, gardeners' hopes. An economically serious pest on cotton, tobacco and soybeans, the tobacco budworm causes serious disappointment for some gardeners. Petunias, carefully transplanted and watered, show only shredded or missing blossoms. Geranium buds promise great color, but after days of waiting for flowers to open, gardeners look closer to find there are no flowers at all. This caterpillar pest has eaten it away, leaving behind a bud of false hope. Tobacco budworm is native to the Western Hemisphere. In nature, it feeds on penstemon, cranesbill, lupines, sunflower, velvetleaf and more. As Europeans settled in America, the budworm welcomed farmers' monoculture of tobacco and cotton. It has been a major pest to these crops and others, causing significant losses. Resistant to many insecticides, tobacco budworm is difficult to control, although recently developed GMO cotton gives some farmers a solution. In landscapes, tobacco budworm most commonly attacks geranium and petunias. With so many host plants, it's only a matter of time before this pest finds your garden. A tobacco budworm's lifecycle includes complete metamorphosis. In early summer, adults emerge from the ground where they survived winter as pupae. Moths (adults) mate and females lay eggs on flower buds. After eggs hatch, caterpillars (larvae) feed on developing flowers and seeds. As the larvae grow, they move from spent flower to new flower, usually at dusk. Infested geranium flower buds simply never open. Petunia blossoms look tattered and unattractive, and the damaged flowers wilt sooner than usual. Budworm caterpillars grow about 1 1/2 inches long after about 4 weeks. These mature caterpillars drop to the soil, burrow 2 to 6 inches deep, and pupate. Depending on soil temperature and other environmental cues, metamorphosis is complete in 2 to 3 weeks. Shorter days or colder temperatures may cue the pupae to remain underground until the next spring. In most of Utah, there are probably two 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 like Sevin. The organic insecticide B.t. (Bacillus thuriengiensis) may kill budworms feeding on petunias as long as the flower buds and other chewed plant parts are covered with the spray. B.t. is less effective on geraniums, since these buds are closed and covered by an outer sheath. Once inside geranium buds, caterpillars can safely eat all they like. Synthetic pyrethrin insecticides are effective, but they also kill many other insects and should be used only as a last resort. Budworms have many natural enemies, including paper wasps, bigeye bugs, minute pirate bugs, damsel bugs and spiders. Picking caterpillars off the plants at dusk helps reduce populations, but it takes a sharp eye to see them. Cold can also help. If tobacco budworm is a recurring problem in a certain area, try to expose pupae to cold winter temperatures. Spade over or till the soil during a dry winter spell. Pupae exposed to temperatures 20 degrees and lower will die. Enditem