Yellow Caterpillars on Sunflower Plants

Pests and Sunflowers

• Two species of caterpillars are considered pests of sunflower production across the United States; they are the thistle and saltmarsh caterpillars. Both types impact a sunflower's leaves and lead to defoliation. Although the thistle can do quite a bit of damage, it is brown with red and orange accents, similar to the coloring of the butterfly it eventually becomes. Only the saltmarsh caterpillar can be yellow in color.

Saltmarsh Caterpillar

• The saltmarsh caterpillar has yellow, brown or black hair or a variation of the three colors. It's often referred to as the "woolly bear" because of its vast amount of hair, according to Carl Patrick, Extension Entomologist with the Texas A&M University System. It's about 2 inches long when fully grown. The pest generally impacts late-planted sunflowers and causes catastrophic leaf destruction, which jeopardizes the overall health of the flowering plant. The caterpillar will eventually transform into a black and white spotted moth with up to 2-inch wingspan.

Management

• You can apply a chemical insecticide on your sunflower plants to control saltmarsh caterpillars. Look for an insecticide with 3-phenoxyphenyl and 2,2-dichloroethenyl or 2,2-dimethylcyclopropane carboxylate as its active ingredients. Follow the instructions on the bottle for proper application. You can also attempt to disturb caterpillar invasion by digging a ditch or placing a physical blockade around sunflowers, notes the University of Florida Entomology and Nematology Department, Featured Creatures website.

Prevention

• Perhaps the best way to prevent infestation by the saltmarsh caterpillar is to plant sunflowers in early spring -- about April after the last frost. This helps to ensure the health of the plant and its ability to ward off infestation of pests. In addition, manually remove weeds before you plant sunflowers and ensure weeds are controlled throughout the sunflowers' growth season. Caterpillars and other pests are more likely to invade plants populated with weeds.