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How to identify it
- Larvae are gray, cream, greenish gray or green with distinct white, yellow, green and brown stripes running the length of the slender body. They are told from other armyworms by a relatively large head with two straight dark bands over the top.[2][1]
- The adult is a yellow-brown or straw-colored moth with a brown or dark streak running the length of each forewing, interrupted near the middle and continuing to the outer margin; the wingspan is 1.2 to 1.5 inches. The 'false' wheat head armyworm, D. terrapictalis, has somewhat darker forewings and substantially darker hind wings.[1][2]
- Larvae hide around the base of the plants during the day and feed on the heads mainly at night, hanging upside down from the awns; damaged kernels are hollowed out, with a small hole bored into the base of the floret.[2][1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Dargida terrapictalis ('false' wheat head armyworm) | A native western species whose larvae and moths look the same; it was trapped with D. diffusa in Oregon and Washington wheat areas, and the moths differ mainly in their darker forewings and much darker hind wings. Its host range and pest status are not known.[1] |
| True armyworm | Other armyworms lack the wheat head armyworm's relatively larger head with two straight dark bands over the top and its slender striped body, and the wheat head armyworm prefers to feed on the heads.[2] |
| Stored-grain weevils | Hollowed kernels with small holes look very similar to weevil damage in stored grain, but wheat head armyworm damage happens in the field before harvest.[1][2] |
Where it lives
Found throughout the United States and Canada and most common in high-producing wheat areas such as Kansas, Nebraska, Oklahoma and Colorado; Dargida damage has been reported in Umatilla County, Oregon, since 2007, Lincoln County, Washington, in 2007 and 2008, and Bonneville County, Idaho, in 2005 and 2006.[1]
Biology and life cycle
The wheat head armyworm overwinters as a pupa in the soil. Moths emerge in spring and within a few days lay eggs on wheat or barley; larvae can be found in wheat from late May, with numbers rising into mid-June as the flag leaf develops. The larvae pass through five instars.[1][2]
There are two generations a year in northern regions. The first generation feeds on foliage and then on the ripening head and pupates in midsummer as the heads ripen; the second moth flight comes in late August, and those moths lay eggs on warm-season grasses in the fall after harvest. Oregon and Washington trapping in 2009 and 2010 recorded two flights, the second much smaller.[2][1]
Larvae feed on a variety of grasses and cereal crops and seem to prefer the heads; timothy is considered a preferred host, and some entomologists suggest it rather than wheat is the preferred crop. Larvae and moths are typically active only at night, and the larvae move toward the base of the stalks during hot days.[2][1]
Damage and signs
- Larvae may feed on all parts of grass and cereal plants but concentrate on the heads, boring a small hole into the base of the floret and hollowing out the kernels. The damage closely resembles stored-grain weevil injury.[1][2]
- The first generation tends to cause undetected but significant damage, which is usually noticed only when damaged kernels turn up at harvest. Infestations are often limited to field margins. WSU spring wheat trials near Davenport, Washington, recorded a 35 percent yield loss attributed to the insect in 2007 and 2008, though economic harm is infrequent.[1][2]
Health risk
The sources treat the wheat head armyworm only as a pest of cereals and grasses and mention no effect on people.[1][2]
Control
Prevention
Scouting is unlikely to be justified unless it is part of an integrated program or the area has had infestations before; Oregon State and Washington State do not routinely recommend spraying at the first sign of the insect, and no scientifically tested economic thresholds exist.[1][2]
Where monitoring is wanted, sweep-net the field margins first, where infestations usually start, and then sweep deeper into the field with a consistent number of sweeps. Sex-attractant pheromone traps placed in or beside the field from late April to midsummer and checked weekly also track the moths; OSU recommends changing lures and insecticidal strips every four weeks. Extension offices can help with identification at least to genus.[1]
Pesticides
No insecticides are specifically labeled for wheat head armyworm in the Pacific Northwest, and the High Plains guide has no chemical control data for it; armyworms appear on many cereal labels, and the insecticides listed for armyworm should be effective. Studies suggest pyrethroids work well but affect natural enemies, so use them with restraint and spray early in the morning or late in the evening while the larvae are exposed and feeding, since daytime applications are likely to be less effective.[1][2]
Common questions
- Why do my harvested wheat kernels look weevil-eaten?
- Wheat head armyworm larvae bore into the base of florets and hollow the kernels while the crop is still standing, which looks very much like stored-grain weevil damage; the first generation usually does this unnoticed in late May and June.[1][2]
- How is the wheat head armyworm different from other armyworms?
- It has a relatively larger head with two straight dark bands over the top, a slender striped body, and a preference for feeding on the heads rather than the foliage.[2]
- Should I spray when I find a few larvae?
- Oregon State and Washington State do not routinely recommend spraying at the first sign, because economic damage is infrequent, infestations are usually limited to field margins and no tested threshold exists; if treatment is warranted, armyworm-labeled contact insecticides applied early morning or late evening should work.[1][2]
Sources
- Oregon State University Extension Service, “Wheat Head Armyworm True or False: A Tale from the Pacific Northwest, EM 9000 (S. I. Rondon, M. K. Corp, D. Roberts, K. S. Pike, P. J. Landolt and D. Keys, May 2011).” extension.oregonstate.edu/catalog/pub/em-9000-wheat-head-armyworm-true-or-false-tale-pacific-northwest (accessed 2026-11-10)
- High Plains IPM Guide (Colorado State University, University of Nebraska, University of Wyoming and Montana State University), hosted by Bugwood, “Wheat Head Armyworm (F. B. Peairs, G. L. Hein and M. J. Brewer), High Plains Integrated Pest Management Guide, Bugwood wiki.” wiki.bugwood.org/HPIPM:Wheat_Head_Armyworm (accessed 2026-11-10)
- iNaturalist, “Dargida diffusa taxon page (order and family).” www.inaturalist.org/taxa/218139 (accessed 2026-11-10)