The Geranium Budworm (Heliothis (syn. Helicoverpa) virescens) is a very serious pest of cotton and tobacco in the more southern areas of the United States, hence its more acceptable name of `Tobacco Budworm'.

In the southern states, this insect's food is almost entirely tobacco for the early broods; later, the caterpillars feed on beggarweed, and to a limited extent on cotton, tomatoes, garden peas and sweet peas. Swan and Papp (1972) report that geranium is the preferred host in California of the later broods of this pest.

While this pest is considered to be a warm-weather, subtropical insect it has been a serious problem to home gardeners, commercial establishments and pesticide applicators on the Front Range of Colorado (East of the Rocky Mountains) for years. This pest invaded Western Colorado in the late 1980's and has been a serious pest of geranium and many other herbaceous flowers in this area since that time.

The favorite herbaceous flower for this insect in Colorado is considered to be the geranium. However, when petunias and geraniums are in the same planting bed, petunias also are eagerly consumed. Impatiens, nicotiana, ageratum, dandelion, marigold and several other bedding plants are also attacked.

The adult budworm moth has light green wings with a series of lighter color bands that span a distance of 1 1/2 inches. Adults lay eggs singly on leaves of targeted host plants during early evening. Eggs are laid on the flower buds of geranium. Other flowers receive their complement of eggs on the leaves. The larval budworms are striped and quite variable in color from dark brown to red or even green depending in part on the plant they are feeding on. Young larvae tunnel primarily through small buds and stems while larger caterpillars chew holes in flower buds, petals and leaves. Larvae take one month to eat their way to maturity. In the Grand Valley of western Colorado (Mesa County) where 180+ day growing seasons are common, two generations a year are normal.

Damage by the larvae includes:

• feeding on developing ovaries and flower buds
• tunneling in plant stems
• feeding on plant leaves and flower petals

Damage to the developing flower buds seriously reduces the show of blooms with some budworm infested plantings producing no blooms during most or all of the growing season. In the insect's early stages of development, the larvae are small enough to tunnel into flower buds and plant stems. The damage by the small larvae as they tunnel through plant stems results in the introduction of various disease organisms into the plant and results in stems that break readily.

The budworm overwinters as pupa in earthen cells several inches beneath the soil surface. In areas where winter temperatures dip below 20 degrees fahrenheit, pupa do not successfully survive the winter. However, soil in areas near buildings, especially on the south side, may not reach temperatures low enough to kill the pupa. Adults normally emerge in late spring.

Budworms can be active year-round in greenhouses and many of these greenhouse infestations may be responsible for some of the budworm pressure in Northern areas where this insect would not normally overwinter outdoors. Budworms can overwinter in the soil of potted plants that were outdoors during the summer months and then taken into the home during the winter. Microclimates around homes and other buildings protected from low temperatures provide niches of survival for overwintering pupa.

Control:

To avoid the use of pesticides hand picking of the caterpillars is strongly recommended. In some areas of the United States, a braconid wasp (Cardiochiles nigriceps) and a sarcophagid fly parasitize caterpillars. Polistes wasps also destroy many larvae, but in Western Colorado these natural control agents are inadequate to control infestations of the Geranium Budworm.

Insecticidal control of the caterpillar has been difficult since they are quite resistant to most insecticides. By 1969 it was reported that Heliothis (Helicoverpa) virescens was practically immune to all available insecticides. Since then new materials have been developed but the smaller larvae have the habit of tunneling inside geranium tissues hiding from the debilitating effects of contact insecticides. Caterpillars on petunias are, however, easier to control than those on geraniums. On petunias this pest normally eats flower petals and leaves and does not tunnel. Insecticides which have shown some degree of success are Orthene, Sevin, the pyrethroids Talstar and Scimitar and the biological control treatment Bacillus thuringiensis. BT materials are relatively host specific and the proper strain of this bacteria must be selected in order to be effective.

Insecticidal treatments should be repeated often to disrupt the life cycle. Alternating insecticides used in these control efforts will help reduce the chances of this pest developing additional insecticidal resistance.

References Used

Cranshaw, W. 1992. Pests of the West: Prevention and Control for Today's Garden and Small Farm. Fulcrum Publishing, Golden Colorado.
Cranshaw, W. & D. Gerace. 1997. Colorado Green.