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Armyworms

Armyworms

Spodoptera and Mythimna species

Insectalso: Fall armyworm, True armyworm, Beet armyworm

Caterpillars that feed in large numbers and march from plant to plant, named for the way they move through a planting like an army. Several species attack gardens, including the fall armyworm, and they can chew up corn, lettuce, tomato, and many other crops, sometimes appearing suddenly in big numbers overnight.

🔎 How to spot it

The caterpillars grow to about one and a half inches and range from pale green to brown to nearly black, with lengthwise stripes; the fall armyworm has a pale upside-down Y on the front of its dark head. Young larvae skeletonize leaves, leaving one surface intact like a windowpane, while older ones chew ragged holes and eat from the leaf edge inward, and on corn they burrow into the whorl and ears. The drab tan moths fly at night.

🥀 Damage it causes

Armyworms defoliate plants and bore into lettuce heads, corn whorls and ears, and the fruit of tomato and pepper, often ruining the harvested part directly. Because they feed as a group and move on once a plant is stripped, damage can be heavy and fast, and a single generation can clear a row of seedlings.

🛡️ Prevent it

Scout often, especially in late summer when fall armyworm flights peak, and check the undersides of leaves for the fuzzy egg masses and tiny young larvae. Keep down grassy weeds that host them, and use floating row cover on vulnerable young plantings. Healthy, promptly harvested crops give the caterpillars less to bore into. Encourage the birds, parasitic wasps, and predatory bugs that feed on them.

🧯 If it is already here

Handpick caterpillars and crush egg masses; on small plantings this is very effective. The organic sprays Bacillus thuringiensis (Bt) and spinosad work well while larvae are still small, and are best applied at dawn or dusk when the caterpillars feed. Large caterpillars are harder to kill, so catch infestations early. Remove and destroy badly infested plants.

💡 Good to know

Armyworms get their name from their habit of moving en masse from a stripped plant to the next, sometimes crossing whole beds. Fall armyworm cannot survive cold northern winters and instead spreads north each year on storm fronts from the south, so outbreaks tend to come late in the season. A range of parasitic wasps and flies attack them and usually keep numbers down.

🌱 Plants it attacks

714 plants in the library can be attacked by this pest

Acorn SquashAdirondack Blue PotatoAdzuki BeanAfrican Blue BasilAfrican MarigoldAgapanthusAgeratumAgrimonyAji Amarillo Pepper🍓Albion StrawberryAlice du Pont Mandevilla🥔All Blue PotatoAlmondAloe VeraAmbrosia CornAmerican BasswoodAmerican Beauty Dragon FruitAmerican BeechAmerican PersimmonAmethyst Falls WisteriaAmish Paste TomatoAnaheim PepperAnemoneAngelique TulipAngeloniaAniseAnise HyssopAnjou PearAnnabelle Smooth HydrangeaAnnual VincaApeldoorn TulipApple MintApril Tryst CamelliaArbequina OliveArizona Sun Blanket FlowerArkin CarambolaArmenian CucumberAroniaArp RosemaryArugulaAshwagandhaAsian PearAsian PersimmonAtemoyaAtlantic Giant Pumpkin🥕Atomic Red CarrotAucubaAugust Beauty GardeniaAunt Molly's Ground CherryAutumn Joy SedumAvocadoBachelor's ButtonBalsam FirBalsam PoplarBanana PepperBarbara Karst BougainvilleaBartlett PearBay LaurelBayberryBeach PlumBeauregard Sweet PotatoBecky Shasta DaisyBee Balm🍅Beefmaster TomatoBenarys Giant ZinniaBengal Tiger CannaBetter Boy Tomato🥬Bibb Lettuce🍅Big Beef TomatoBig Boy TomatoBilberryBing CherryBitter MelonBlack BeanBlack Beauty EggplantBlack Beauty ZucchiniBlack Beluga LentilBlack Cherry TomatoBlack CrowberryBlack Currant🍉Black Diamond WatermelonBlack Kabouli ChickpeaBlack Krim TomatoBlack RaspberryBlack Sapote🥬Black Seeded Simpson Lettuce🥕Black Spanish RadishBlack Tartarian CherryBlack WalnutBlack-Eyed PeaBlack-eyed Susan VineBlood OrangeBloomsdale SpinachBlue Bird DelphiniumBlue Bird Rose of SharonBlue FescueBlue Lake Green BeanBluecrop BlueberryBocking 14 ComfreyBok Choy

For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.