Home gardeners who wish to grow flowers with colorful blooms often plant chrysanthemums, more commonly known as mums. Members of the daisy family, mums typically bloom from late summer through the early part of fall. While mums are fairly pest resistant, they are susceptible to infestations of caterpillars which feed on mum foliage and flowers.
Caterpillars are the most damaging pest of garden mums. Beet armyworm caterpillars are green or black, hairless and have yellow strips running along each side of the body. Mottled gray moths are the adult form of this pest that only live four to seven days. Moths lay their eggs on the undersides of host plant leaves, where they hatch into caterpillars that feed on mums. Corn earworms also damage mums by feeding on them. Adult forms are light brown in color that live 15 to 30 days and lay up to 35 eggs on host plants each day. After hatching, larval forms search for a place on host plants to feed. Immature larvae are typically brown, green, black, yellow or pink.
Beet armyworms feed on the foliage of infested mums, skeletonizing leaves and leaving the large leaf veins intact. Heavy infestations of beet armyworms can defoliate entire plants. Corn earworms feed on a variety of garden plants, including garden mums and vegetable crops. Feeding injuries often occur on flowers, buds, stems and leaves of infested mums. After defoliating one plant, corn earworms may move on to another host plant and begin feeding.
Both caterpillars have natural enemies that feed on them, keeping them under control. Some natural predatory insects include big-eyed bugs, minute pirate bugs, parasitic wasps and green lacewings. Beet armyworms are susceptible to a virus that causes them to become limp, turn black and die. Light caterpillar infestations may be controlled by removing caterpillars by hand. Place them into a bucket of soapy water after hand-picking them from your mums.
Heavy infestations of caterpillars may require chemical control methods to prevent serious mum damage. Insecticides are warranted if five to 10 caterpillars are found on plants. Your local garden center has a variety of insecticides that kill caterpillars. Choose a product with the active ingredients malathion, permethrin or methomyl for best results.