The garden webworm (Achyra rantalis) attacks a wide range of crops including strawberries, legumes, corn, cabbage, spinach, cucumbers, and beets. They also occur on several weeds, including the lambsquarter, pigweed, and dock. Pigweed is a preferred host plant for webworms, especially, the garden webworm. The caterpillars make shelters of loose webbing and feed on leaves.
They are about 1 inch long when fully grown. The color is yellowish green when young with prominent dark spots and a yellowish head. Adults are white to brown moths with dull yellow to brown coloration plus both pairs of wings have light and dark markings. Eggs are small, yellow or green in color, and laid in groups of 2 to 20 on the underside of leaves.
Young larvae consume large amounts of foliage by skeletonizing leaves and can completely defoliate plants in a short period of time. As they devour leaves, webworms spin a web drawing leaves together or folding individual leaves together to form a tube in which they hide when disturbed. Slender worms move backwards rapidly when disturbed.1,2
Severe infestation can weaken or kill plants. Several generations are produced during the growing season. Pupae pass winter in the soil and emerge in early spring. Injury and defoliation appear to be worse when weeds are around. Therefore, keep your garden weed-free, particularly from pigweed and lambsquarters.2
For corn use Insecticides Approved for Application on Corn for Garden Webworms. Observe specific label guidelines in regard to usage restrictions and application techniques.
Image Credits: Alton N. Sparks, WikiMedia