- Raspberry horntail caterpillars are black or black and yellow in color, up to 1/2 inch long. The larvae and adults feed on rosebushes and may prevent flowers from blooming. Adults lay eggs on canes in spring from April to June. Prune all canes affected by raspberry horntail to prevent eggs from hatching and avoid infestation. If adult caterpillars are present, treat the shrubs with pesticides.
- Fall webworm larvae are pale yellow in color. After eggs hatch in summer, the larvae feed on shrub and plant foliage. Both blackheaded and redheaded fall webworms are found in North America. The adults are white, but in larval stages they look like small, yellow worms. Fall webworms survive the winter and come out of dormancy in late May. Adults lay eggs on the undersides of leaves, where they hatch in approximately one week. As larvae mature, they feed heavily on leaves and cause extensive damage.
- The American lady butterfly, also known as American painted lady and painted beauty, creates larvae that look like yellow worms. The larvae may be mostly yellow with thin black stripes on them. Butterfly larvae feed heavily on foliage, but damage does not become dangerous unless there are very large populations of butterflies. Look for butterfly nests and remove them to prevent American lady larvae.
- Prevent worms and other pests from invading your shrubs by selecting companion plants to keep them away. Aster, chrysanthemums, dill, mint, thyme, sage and borage all repel worms and other undesirables. Good crop rotation also prevents pest infestation. Keep the area around shrubs free of debris and weeds that may attract worms, caterpillars and other pests. A layer of mulch under shrubs attracts beneficial beetles that eat larvae, worms and other pests.
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