Geranium budworms, also called tobacco budworms or Heliothis virescens, feed on geraniums in warm climates. The adult budworm moth lays eggs on the leaves and flowers of a geranium. Upon hatching, the larvae and caterpillar tunnel their way through the plant, damaging the flower and leaving the plant vulnerable to disease.
Geraniums may bloom sparsely or not flower at all if budworm larvae eat young flower ovaries. The larvae also tunnel into plant stems, causing them to break off easily, and leave visible damage when they eat the leaves and existing flowers of the geranium. Small holes in stems or black droppings on leaves may indicate a budworm infestation.
Budworms can survive winter by burrowing into the soil of potted plants brought indoors. Before bringing potted geraniums indoors for the winter, change the soil to prevent providing a safe home for these damaging insects.
Gardeners should remove caterpillars and larvae from geraniums by hand, as they resist applications of most insecticides. During the day, budworms cluster around the base of the plant for shelter. They emerge to feast on the plant during the early evening hours, making this the best time for hand removal.