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

Bug Control Recommendation Tool

What type of pest are you dealing with?

Ants Cockroaches Termites Mosquitoes Bed Bugs Spiders Other

How severe is the infestation?

A few sightings Several sightings weekly Several sightings daily Large numbers, causing damage Unknown but suspect a large number

Do you require child/pet/garden safe treatments (organic)?

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Are you willing to monitor and maintain the treatment yourself?

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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.