A tiny pest that causes home gardeners grief each year is already establishing itself in many landscapes, although it's full impact won't truly be felt until later this summer. The intruder is the tobacco budworm, Heliothis virescens, also known as the geranium budworm. A serious pest of tobacco and cotton in the south, geranium budworm prefers to attack the flowers of Solanaceous plants in Nebraska gardens, such as petunia and nicotiana, but will also feed on geranium, rose and many other flowering plants. Some gardeners have such severe problems with this insect, that they have stopped growing geraniums or petunias.
This bothersome insect is the larval stage of a "cutworm" type moth. Adult wingspan is 1 ½ inches, and the wings are light green with brownish shading and crossed by four wavy, cream-colored bands. The caterpillars are quite variable in color, partly based on the flowers they eat, so may be nearly black, pale brown, green or reddish. Dark colored bands run down the caterpillar's back. When fully grown the caterpillars may reach 1 ½ inches long.
Geranium budworms attack the buds of developing flowers, but only rarely feeds on plant leaves. Eggs are glued by female moths on the leaves or flower buds of preferred plants, and after hatching the tiny caterpillars tunnel into the stems and developing flower buds. Damaged flowers fail to open, dry up and die. Older caterpillars eat entire flower buds and feed on the petals, giving flowers a ragged appearance. Severely affected plants may produce few, if any, viable flowers during the summer.
Geranium budworms are a warm-weather, subtropical insect but can survive Nebraska winters as pupa in the soil of protected microclimates around the home, such as patios or courtyards. Areas with concrete surfaces that hold heat would also be good locations for budworm overwintering. Budworms can be active year-round in greenhouses, so some infestations may originate on plants purchased in spring. Finally, budworms can survive in the soil of container plants that are taken indoors in fall and overwintered in the house, or containers of tender perennials that are overwintered in the garage.
Two generations of budworm occur each summer, with the first emerging in late spring. The second generation, which appears in August and early September, is the most damaging and is when many homeowners really begin to take notice.
To control geranium budworms without pesticides begin by monitoring flowerbuds for tunneling by the first generation of insects in early summer. Handpick caterpillars when they are noticed, and drop them into a can of soapy water, or remove the entire flower head and discard it. Keep a vigilant watch on your plants throughout the summer.
Repot plants before taking them inside for winter to eliminate overwintering pupae. Discard old soil in outdoor containers with a history of budworms.
Insecticidal control can be problematic, particularly on geraniums, where caterpillars are protected from applications inside the flowerbuds and stems. Consider planting ivy geraniums instead of standard geraniums; they are less frequently damaged.
Insecticidal control is easier on petunias and the synthetic pyrethrin insecticides can provide good control. Look for products containing the active ingredients permethrin, cyfluthrin, or bifenthrin. Read and follow label directions, and repeat applications as directed on the label.