Most recently reviewed by: Dalton Ludwick & Holly Davis (2020)
Common Name(s): Corn earworm, Cotton Bollworm, Soybean Podworm, Tomato Fruitworm
Corn earworm belongs to the Order Lepidoptera (butterflies, moths and skippers) and the adult stage is a stout bodied, brownish to buttery-yellow moth with a wingspan of about 1 1/4 to 1 1/2 inches. There are usually darker bands present near the tips of the front and hind wings.
There are six larval instars (or stages). The first instar is about 1/16” long and the the 6th instar can grow to 1 3/4 inches long. There is no one color for the larvae, and they can range from yellow to pink to green. Regardless of coloration there will be a darker stripe down the midline of the top of the larva, and somewhat wider stripes on the lateral edges of the body when viewed from above. A yellowish band is often found on the side of the larvae, and the band contains the dark, circular spiracles, the holes that let air into the insect’s body. Larvae have many microspines on the back and sides of the body, and these are not found on other common corn caterpillar pests. The head is orange to tan but may be more brownish in some larvae.
Origin and Distribution
Corn earworm is native to the New World and overwinters in Texas, has multiple generations here, and is a threat throughout the growing season. In the United States, it is thought to be able to overwinter south of about 40 degrees north latitude, but as the summer progresses the moths fly north and infest the entire country and some of Canada.
Habitat & Hosts
Corn earworm has an extremely wide food host range and can be found wherever its host plants grow. There are many non-crop plants on which the earworm can develop early in the year before crops and gardens are planted. Cultivated hosts include sweet corn, field corn, green beans, snap beans, cowpea, peas, peppers, eggplant, lettuce, sweet potato, rice, cotton, grapes, strawberry and many others. Typically the “worm” in sweet corn is the corn earworm. Corn earworm is also a very significant pest in hemp or cannabis production, and it is not uncommon to find larvae consuming buds and leaves.
Eggs are laid singly on host plants. These are pearly white when laid and become somewhat more yellow over the course of the three days or so before they hatch. The larval stage, comprising six larval instars, lasts 12 to 15 days during the warm part of the growing season, longer when it is cooler. When fully grown, the 6th instar larvae leaves the host plant, burrows into the ground and enters the pupal stage which lasts 10 – 15 days during the summer. Adults emerge from the ground, mate and disperse to lay eggs. Sometimes they disperse very
long distances on storm fronts. Moths consume liquids and nectar as food and they are not damaging to plants.
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
Management practices differ depending on which crop is being damaged. On field corn and sweet corn, the eggs are laid on silks, and the newly hatched larvae feed down the silk channel and then on the tip of the ear. In this case there is little opportunity to use insecticides because the larvae are in protected spaces. If insecticides are to be used, then they should be applied at the time of egg laying, usually with repeated applications from the time of silking until after the brown silk stage is reached.
Control is more straightforward when the earworms are feeding on the outside of the leaf or fruiting structure. In this case, sprayable formulations of Bacillus thuringiensis can be applied if a least toxic control method is desired. It must be noted, however, that corn earworms are now resistant to many of the Bt toxins in these sprayable insecticides because they built up resistance to them on Bt (GMO) corn in the last 25 years that corn has been used in the US. Synthetic pyrethroids can be effective, especially on smaller larvae, but it is also the case that corn earworms have developed significant levels of resistance to synthetic pyrethroids due to their widespread use in agriculture. Chlorantraniliprole is highly effective on corn earworm larvae, even large larvae. Spinosad and Spinetoram are very effective as well, as is the old insecticide carbaryl (Sevin). Agricultural producers have more options available and should consult a crop-specific control guide.
Corn Earworm. University of Florida Featured Creature: http://entnemdept.ufl.edu/creatures/veg/corn_earworm.htm.