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Sarah Browning

Sarah Browning, columnist

GWYNETH ROBERTS/Lincoln Journal Star

A tiny pest that causes gardeners grief each year already is 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 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.

Description

This bothersome insect is the larval stage of a "cutworm" type moth. Adult wingspan is 1½ 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 they 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 1½ inches long.

Damage

Geranium budworms attack the buds of developing flowers, but only rarely feed 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.

Life cycle

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 also would 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.

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Two generations of budworms 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.

Control

To control geranium budworms without pesticides, begin by monitoring flower buds for tunneling by the first generation of insects in early summer. Hand-pick 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 with a history of budworms in outdoor containers.

Insecticidal control can be problematic, particularly on geraniums, where caterpillars are protected from applications inside the flower buds and stems. Consider planting ivy geraniums instead of standard geraniums; they are less frequently damaged.

Insecticidal control is easier on petunias, and synthetic pyrethrin insecticides can provide good control. Look for products containing the active ingredients permethrin, cyfluthrin or bifenthrin.

And as always, read and follow label directions, repeating applications as directed on the label.

Sarah Browning is an Extension dducator with University of Nebraska-Lincoln Extension in Lancaster County. Reach her at 402-441-7180; 444 Cherrycreek Road, Suite A, Lincoln, NE 68528; or sbrowning2@unl.edu.

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