Cutworm vs Armyworm: A Gardeners’ Guide to Battling Pests

Cutworms and armyworms are common pests that can cause significant damage to various crops and plants. Both belong to the family Noctuidae and are caterpillars of nocturnal moths. Understanding their similarities and differences can help farmers and gardeners better manage these pests.

While cutworms and armyworms may look alike, they have distinct behaviors and feeding patterns. For instance, cutworms typically feed at night, hiding in soil or plant debris during the day. Armyworms, on the other hand, can feed both during the day and night. The larvae of these pests can be identified by their size, color, and markings.

Managing these pests involves monitoring their presence, scouting fields, and implementing pest control measures when necessary. The earlier they are detected, the more effectively growers can protect their crops from significant damage.

Cutworm and Armyworm Overview

Identification

Cutworms:

• Heavy-bodied, night-flying moths
• Larvae are up to 2 inches (5 cm) long
• Can be pale greenish-gray to brown in color
• Curl up and lie still when disturbed

Armyworms:

• Heavy-bodied, night-flying moths as well
• Have a wingspan of 1½ to 1¾ inch
• Forewings are dark gray-brown with distinct markings
• Hind wings are light gray-brown with a whitish fringe

Life Cycle

Cutworms and Armyworms

• Eggs: white or greenish, laid in masses, darkening when approaching hatching
• Larvae: Feed and grow, undergoing molting stages
• Pupae: Transform into adult moths

Damage

Cutworms

• Primarily nocturnal feeders
• Damage seedlings, young plants, or vegetables
• Cut stems at or near the soil surface

Armyworms

• Attack grasses, small grain crops, corn, alfalfa, beans and more¹.
• Damage crops by chewing on foliage, sometimes causing complete defoliation²
• Can clip heads of small grains and feed on seed heads of cereals

Pest Management Strategies

Monitoring

Monitoring is crucial for both cutworms and armyworms. Regular field scouting helps identify early signs of infestation. Trapping is another method that can be used to detect their presence. For example, pheromone traps can be effective in attracting adult moths.

Setting up traps:

• Place in fields prior to crop emergence
• Check traps every 3-5 days
• Maintain trapping throughout the season.

Cultural Control

Cultural control methods focus on reducing pest populations through practices that limit their establishment and reproduction. These practices can include:

• Proper field sanitation: Clean and destroy leftover crop debris
• Crop rotation: Alternate between host and non-host plants
• Timely planting: Synchronize crop growth with pest-free periods
• Tillage: This can reduce the number of larvae in the soil.

Biological Control

Biological control methods involve introducing or conserving natural enemies of pests, such as:

• Predatory insects (e.g., beetles and lacewings)
• Parasitic wasps, which attack pest larvae
• Entomopathogenic nematodes, which target pest larvae in the soil.

Examples of natural enemies:

• Steinernema carpocapsae: A nematode effective against cutworms
• Trichogramma spp.: Tiny wasps that parasitize the eggs of armyworms.

Chemical Control

Chemical control involves the application of pesticides and insecticides to manage pest populations. These measures should be used judiciously as part of an integrated pest management (IPM) strategy. IPM focuses on using chemical controls only when necessary and considers the environmental impacts.

Methods to reduce pesticide use:

• Apply only when pest populations reach economic thresholds
• Utilize selective pesticides targeting specific pests
• Rotate pesticide classes to prevent resistance.

Comparison Table: Cutworm vs Armyworm

Specific Crop Considerations

Corn

• Armyworms: Known to infest whorl-stage corn, resulting in defoliation or stalks and leaf midrib consumption. More on armyworm in corn
• Cutworms: Can damage seedlings by cutting stems near the soil surface.

Alfalfa

• Armyworms and Cutworms: Both pests can feed on alfalfa leaves, potentially causing defoliation and impacting crop yields. More information on managing these pests in alfalfa

Small Grains

• Armyworms: May completely defoliate young small grain plants and clip seed heads of cereals and forage grasses.

Sugarbeets

• Army Cutworms: Can cause damage to sugarbeets by feeding on foliage, potentially reducing yield. More details on army cutworms in sugarbeets

Canola

• Armyworms and Cutworms: Both pests can impact canola by feeding on the foliage, potentially causing reduced crop yield. Pest management tips for canola crops

Peas

• Armyworms: Can feed on pea plants and cause significant crop loss if left untreated.

Turfgrass

• Fall Armyworms: Known to cause rapid, significant loss of leaf tissue in bermudagrass, ryegrass, fescue, and bluegrass. Identification and control tips for fall armyworm in turfgrass

Comparison Table

Signs of Infestation and Treatment Thresholds

Field Scouting

Field scouting is crucial for detecting infestations of cutworms and armyworms in crops such as corn and small grains. Start scouting as soon as the crop emerges and continue twice weekly until plants reach 18 inches high¹. Look for signs of damage like:

• Holes in leaves
• Clipped stems
• Presence of larvae

Dethatching

Dethatching removes the thatch layer, which consists of dead grass and organic debris, providing a habitat for cutworms and armyworms. This method helps minimize infestations by:

• Exposing larvae to natural predators
• Reducing available food sources
• Improving irrigation and airflow

Drench Test

A drench test helps detect the presence of cutworms and armyworms in the soil. Here’s how to do it:

1. Mix one gallon of water with one tablespoon of liquid dish soap.
2. Pour the mixture over a one-square-foot area of infested soil.
3. Observe the area for 10 minutes and count the number of larvae surfacing.

Economic Thresholds

Economic thresholds help determine when pest control measures become cost-effective. For example, an economic threshold for armyworms in corn is 25% of plants showing damage with larvae still present². Base treatment decisions on factors like:

• Larvae density
• Crop value
• Pest control costs

Comparison Table: Cutworm vs Armyworm

Effective Treatment Options

Bacillus Thuringiensis

Bacillus Thuringiensis (Bt) is a naturally occurring soil bacterium. It works by producing proteins that are toxic to specific pests like armyworms and cutworms.

• Pros:
  • Biological control
  • Targets specific pests
• Cons:
  • May not be effective against all species

Spinosad

Spinosad is a fermentation product derived from a soil bacterium. It targets the nervous systems of pests like armyworms and cutworms.

• Pros:
  • Low toxicity to humans and other mammals
  • Biodegradable
• Cons:
  • Requires proper timing of application

Steinernema Carpocapsae

Steinernema carpocapsae is a beneficial nematode that parasitizes various pests, including armyworms and cutworms.

• Pros:
  • Biological control
  • Safe for humans, pets, and beneficial insects
• Cons:
  • May not work well in hot, dry conditions

Carbaryl

Carbaryl is a chemical insecticide that works on the nervous system of pests, such as armyworms and cutworms.

• Pros:
  • Broad-spectrum control
  • Fast-acting
• Cons:
  • Toxic to beneficial insects
  • Possible human health risks

Spot Treatments

Spot treatments involve targeting specific areas where pests are a problem, rather than treating the entire area.

• Pros:
  • Reduced pesticide use
  • Saves time and resources
• Cons:
  • May miss some infestations

Cutworm and Armyworm Species

Black Cutworm

• Larvae: Black cutworm larvae are plump, hairless, and grow up to 1.5 inches long, with a characteristic black-grey color. When disturbed, they tend to curl up.
• Eggs: Black cutworm eggs are typically laid in masses and start with a white or greenish color, darkening as they approach hatching.

Black cutworms are known for their infestation on fields in North Dakota and can be a real pest, damaging crops by cutting off the plant at the base.

Variegated Cutworm

• Larvae: Variegated cutworm larvae grow up to 2 inches long, have a yellowish-brown to black color, and a distinctive row of yellow spots along their backs.
• Eggs: Similar to black cutworms, variegated cutworms lay eggs in masses, with colors transitioning from white or greenish to darker shades as they hatch.

Variegated cutworms often feed on the foliage of plants and can result in significant crop damage.

Army Cutworm

• Larvae: Army cutworm larvae are greenish-gray with a subtle stripe pattern along their backs, growing up to 2 inches long.
• Eggs: The eggs of army cutworms are laid in masses, similar to the other cutworm species, with a white or greenish color that darkens as they approach hatching.

Army cutworms are differentiated by their similar eating habits to armyworms, primarily attacking grasses and cereals. They have a wide range of host plants, including small grains, corn, and rice.

Comparison Table

Birds and other natural predators play a role in keeping both the cutworm and armyworm populations under control. Vigilance and properly timed action can be key in managing cutworm and armyworm infestations in agricultural and residential settings.

Supporting a Healthy Turf and Landscape

Parasitic Nematodes

Parasitic nematodes are beneficial organisms that can help control cutworms and armyworms. Some examples are:

• Steinernema carpocapsae
• Heterorhabditis bacteriophora

These nematodes enter and kill the pests, making them effective natural control agents. Advantages of using nematodes include:

• Targeted pest control
• Environmentally friendly
• Safe for humans and pets

Possible drawbacks might be:

• Temperature sensitivity (optimal temperature range varies by species)
• Limited shelf life

Cultural Practices

Practicing good turf and landscape management can reduce the impact of cutworms and armyworms. Some helpful cultural practices include:

• Regular mowing at proper height
• Keeping grass healthy to withstand minor damage
• Removing excess debris or plant litter around turf

By maintaining a clean and organized landscape, pests will have fewer hiding and breeding spots.

Irrigation Management

Proper irrigation is crucial for healthy turfgrass and reducing the risk of cutworm and armyworm infestations. Overwatering can create a favorable environment for pests. To maintain proper moisture levels:

• Water deeply, but infrequently
• Water early in the morning to allow time for the grass to dry
• Adjust watering schedule based on weather conditions

In conclusion, by using a combination of parasitic nematodes, cultural practices, and proper irrigation management, it is easier to maintain a healthy turf and landscape with reduced infestations of cutworms and armyworms.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Flame Tree Loopers from Guam

Subject: caterpillars everywhere!
Location: Guam
November 10, 2013 11:20 pm
Happened to step outside on my front porch and noticed a rather large gathering of these wormy looking fellows hanging around everywhere. Probably over 200 of them all along the driveway. They vary in size, but are all quite small (the largest I found was maybe an inch long?).. Very active, it was hard to take a picture of one since they were all moving pretty quickly. No idea where they came from, or when they even showed up.
Usually bugs come out in droves here when it rains, but it was a pretty dry day when I saw them. Nov 11 @ around 4pm.
Signature: JB

Hi JB,
The red heads on your caterpillars are very distinctive and it shouldn’t make identification too difficult.  We are preparing your posting and then we will research the species.

Our quick search did not produce any potential matches.  We will try again later and perhaps one of our readers will be able to assist in this matter.

Thanks for the quick response! I’m excited to see what they are.. they disappeared as quickly as they came.. Don’t know if that is due to the large amount of geckos we have hanging around that enjoyed an all you can eat caterpillar buffet, or for some other reason. Maybe we will see a large explosion of moths or butterflies around our home soon! 🙂

Karl identifies Flame Tree Loopers
Hi Daniel and JB:
They look like Poinciana Loopers or Flame Tree Loopers (Pericyma cruegeri). These are Noctuid moths in the Family Erebidae or Noctuidae, depending on whether you prefer the new or old classification system. Similarly, the subfamily designation is either Erebinae or Catocalinae. The species is native to much of Southeast Asia and Australia but has been introduced to several Pacific islands, including Guam. As the name suggests, the caterpillars feed on Poinciana or flame Tree species, particularly the Yellow Flame Tree (Peltophorum pterocarpum; native to Southeast Asia) and the Royal Poinciana or Flamboyant (Delonix regia; originally from Madagascar). Both are now grown as ornamental trees throughout the tropical regions of the world and the Poinciana Looper is considered a serious pest of these tree species. There are at least two color morphs; one is predominantly green and the other is mostly black and white as in JB’s photos. If you want to learn more about the biology of these moths you can check out two online papers: “Biology of the Poinciana Looper, Pericyma cruegeri (Butler) on Guam” by R. Muniappan (1974); and, “Tree Pests of the Marianas” by Donald Nafus (U.S. Department of Agriculture). Regards.  Karl

Awesome!! So great to learn what these little guys were… not so great that they are an invasive pest! I ended up losing about 6 hours of my day looking at various bugs and caterpillars and now I can be at peace! Thanks so much for the detailed and informative answer. 🙂

Letter 2 – Dice Moth Caterpillar from South Africa

Subject:  Unknown
Geographic location of the bug:  Marloth Park, South Africa
Date: 01/02/2018
Time: 11:49 AM EDT
Good day.
Found this gorgeous worm outside. It seems to be trying to find its way with the “paddles” on the back, might be hugely mistaken though. Was wondering if you could assist me as I cannot find help on the internet? Would like to know how the butterfly looks.
Kind regards
How you want your letter signed:  Yolande

Dear Yolande,
Your Caterpillar is very similar looking to the North American Paddle Caterpillar in the Owlet Moth family Noctuidae, that we figured it might be closely related, and that led us to this posting of some Dice Moth Caterpillars in the Rhanidophora on the Biodiversity on my Farm site.  iSpot also contains some nice images of Rhanidophora ridens, the species that looks most like your individual.  Alamy also has a nice image.

Letter 3 – Cutworm or Armyworm

I know you’re busy, but look at my new buddy!
So I brought my pond plants inside over a week ago since the temps have started dropping rapidly. Today, I noticed a creature munching on my lizard’s tail plant. I really dig catepillars, so I don’t want to let him go outside because it’s been frosting at night. Can you give me an ID when you get a chance? This guy hails from west-central Illinois. I’m thinking that it’s some sort of Sphinx moth? I was tapping his rear to get him to move off of his leaf and he turned around and tried to get my finger!! I think I’ll set him up in an enclosure of some kind for I fear that he’ll perish in the temps right now. Thank you for your time, I appreciate it, and just like everyone else, I’m OBSESSED with WTB
Erika

Hi Erika,
We have always just generically referred to this group of Owlet Moth Caterpillars in the family Noctuidae as Cutworms. BugGuide likes the more specific name Armyworm. Here is what Charles Hogue writes about the group: “All are general feeders and will eat most kinds of low-growing herbaceous vegetation, including grasses. The adults are all drab brown or gray moths with pale translucent hind wings. The fore wings have varied markings, but in many species there are noticeable found and kedney-shaped spots near the leading edge.” They are called Cutworms because they will cut a newly sprouted plant at soil level killing it. They are called Armyworms as they are sometimes found in large numbers that travel like army troops..

Letter 4 – Cutworm of a Tomato Moth eating Tomatoes in Jamaica

Subject:  Tomato caterpillars
Geographic location of the bug:  St. Elizabeth, Jamaica
Date: 04/09/2018
Time: 09:04 AM EDT
Your letter to the bugman:  Hello Bugman!
I’ve  been enjoying your website for years  and I am now excited to submit my first question! I am a Peace Corps volunteer serving in Jamaica and my host father is growing some of the most beautiful tomatoes in the entire world. However there is an aggressive caterpillar pest Wreaking havoc on his produce. I am trying to encourage less toxic methods to deal with such pests in the community and I was hoping that you could identify the species of caterpillar for me in order to create a more targeted management method. Thank you so much for your help and keep up the good work!
How you want your letter signed:  Farming PCV

Dear Farming PCV,
This is some species of Cutworm in the family Noctuidae, and many caterpillars in the family look very similar.  Our internet search did turn up images on Minden Pictures of the Caterpillar of the Large Yellow Underwing, Noctua pronuba, feeding on the leaves of a tomato plant, and BugGuide states “Larvae feed on a variety of crops and vegetables, plus grasses”, but even though we see a similarity, we do not believe that is your species.  We found an image on Colourbox that is identified as a Turnip Moth cutworm, Agrotis segetum, eating a tomato, and it resembles your culprit, but other images of this caterpillar we located on the internet are brown and we cannot confirm that identification either.  Both species we have mentioned are Old World species, but the Large Yellow Underwing has been introduced to North America.  We found additional images of brown Cutworms eating tomatoes on Dreamstime and then we believe we found your culprit on Alamy where it is identified as a “Bright-line Brown-eye moth, also known as tomato moth (Lacanobia oleracea).”  According to UK Moths: “Favouring suburban habitats as well as salt-marshes, the larval foodplants in the wild are usually orache (Atriplex) and goosefoot (Chenopodium), but it can sometimes attack cultivated tomatoes, feeding internally in the fruit.”  Wikipedia does not list Jamaica nor any other New World location, but that does not mean the species has not been introduced.  It might just be undocumented at this time.  Wildlife Insight offers the following advice:  “To prevent the adult moths from laying eggs on the plants some fine mesh should be placed over the greenhouse windows between May and August. Doors left open during the day to allow bees to enter should be netted off if left open at night.  If growing tomatoes outdoors then the whole plant will have be cloaked in netting.  Any clusters of eggs are usually easy to find on the underside of the leaves and can then be scrapped off.  At the first sign of fenestrations appearing in tomato leaves check the undersides for the tiny caterpillars.  The location of the feeding caterpillars is often given away by fine dark freckling of frass on the leaves directly beneath those being eaten.”

Thank you so very much for your assistance!

Letter 5 – Dot Moth Caterpillar

Subject: Caterpillar
Location: nr Carmarthen
August 18, 2017 6:42 am
A couple of people have identified this caterpillar as ‘Dot moth’.
Signature: Dara

Dear Dara,
Please add WTB? to the the list of people who agree that this is a Dot Moth Caterpillar, Melanchra persicariae.  According to Wildlife Insight:  “The caterpillars reach 45mm in length and can be various shades of green and brown. The distinguishing features are three pale lines cross the dark prothoracic plate behind the head, the central one being an extension of dorsal line and the eleventh segment is raised dorsally.  The Dot Moth caterpillar feeds on a wide range of herbaceous plants and sallows and can be found during the day on plants such as dock and common nettle.”

Letter 6 – Harris's Three Spot Caterpillar

Help!
I failed to mention earlier that we’re in Greensboro, NC and the little guys are over 2 inches long. This caterpillar, yes, that is a caterpillar, is eating my fringe tree which is very small and can’t take much more! there are five of these and I don’t want to kill them if they are going to turn into some lovely butterfly or moth…. it’s head is to the right, with the three hairy brown balls hanging off of it….lower left is its back end.
Melissa

Hi Melissa,
Probably 15 letters will go unanswered because we spent so much time trying to identify your bizarre caterpillar. We were relatively sure it was an Owlet Moth in the family Noctuidae, one of the largest moth families. We scoured BugGuide until we located Harris’s Three Spot, Harrisimemna trisignata. The hairy balls are actually “old dry head capsules shed by the earlier instars!” The adults are a very lovely moth, also pictured on BugGuide.

Letter 7 – Hitched Arches Caterpillar

Hitched arches moth caterpillar
Location: Shenandoah National Park, Front Royal, Va
September 26, 2011 9:07 pm
Hello, bugman:
My husband and I wanted to share this picture of a very beautiful caterpillar that we found feeding on goldenrod yesterday in Shenandoah National Park. We were able to identify it as the hitched arches moth caterpillar through the BugGuide. We have never seen anything like it.
Signature: Peggy

Hi Peggy,
With the onset of autumn, our mailbox is filling with caterpillar identification requests and spider identification requests.  Thanks so much for taking the time to self identify your Hitched Arches Caterpillar, Melanchra adjuncta, and also for taking the time to email the photo to our website.  BugGuide is an awesome source for insect identifications.

Letter 8 – Hitched Arches Caterpillar on Aster: Melanchra adjuncta

Subject: green caterpillar
Location: 30 miles from charlottesville Va in mountains
October 26, 2013 5:35 pm
Need id. Cat on an aster in blue ridge mountains.. oct. 18 . Near charlottesville
VA. Cant find name in wagners or on web sites. Thx
Signature: nancy n

Hi Nancy,
Since you indicated this caterpillar was feeding on Aster, we checked the species of Hooded Owlet Moths in the genus Cucullia that are posted to BugGuide, but we could not find a match.  We hope one of our readers can assist in this identification.  Are you certain this is an aster?  There appear to bee seed pods on the plant and asters do not have seed pods.

I often take cat off of host plant to get picture and then return it. We found 6 of them on six different aster plants tho.  I dont know which aster variety.  Keep looking please.  Ive looked at all my resources. N

IM SENDING A FEW MORE PICS OF MY MYSTERY ASTER MOUNTAIN CATERPILLAR….NANCY  NEWMAN

Hi again Nancy,
We have added your additional photos to the posting.

Hitched Arches identification courtesy of a comment by Frankie
Thanks Frankie,
You are absolutely right. The Hitched Arches is the perfect match based on the photos posted to BugGuide. We are going to update the posting thanks to your carefully researched comment.

Thanks to all of you who identified the Hitched Arches caterpillar for me.   What an amazing job you do!
N Newman
Nnature642