Yellow striped armyworms can be a real nuisance, damaging various crops and making it difficult for farmers and gardeners alike. These pests, scientifically known as Spodoptera ornithogalli and Spodoptera praefica, are found throughout the United States, primarily affecting alfalfa, tomatoes, and other crops.
If you find yourself dealing with a yellow striped armyworm infestation, there are a few techniques you can employ to protect your garden or farm. Examples of effective methods include biological control, chemical treatment, and cultural practices. Timely pest monitoring is crucial for early detection and the swift application of appropriate measures.
Identifying Yellow Striped Armyworms
Yellow striped armyworms, scientific name Spodoptera ornithogalli, are caterpillars that eventually transform into moths. They are named for the distinctive yellow dorsolateral line running the length of their body. Here are some features of these caterpillars:
- Length: Can reach up to 1.5 inches
- Color: Dark gray to black body
- Stripes: Prominent yellow stripes on the sides
Adult moths have a few notable features as well:
- Wingspan: Roughly 1.5 inches
- Color: Brown mottled forewings, pale hindwings
- Markings: Kidney-shaped marking on forewings
The life cycle of a yellow striped armyworm has four main stages: eggs, larvae, pupae, and adult moths. The larval stage is when they are most destructive to crops, while adult armyworms are mostly harmless. Here’s a brief overview of the life cycle:
- Eggs: Females lay clusters of eggs on host plants
- Larvae (caterpillars): Hatch from eggs, feed on foliage and cause damage to crops
- Pupae: Transform in underground cocoon-like structure, preparing to become adult moths
- Adult moths: Emerge from pupae, mate, and lay eggs
Multiple generations of armyworms can occur each year, making them a persistent problem for many crops. Yellow striped armyworms share similarities with their close relative, the fall armyworm, in terms of size, color, and feeding patterns.
|Yellow Striped Armyworm
|Dark gray to black
|Pale brown to black
|White inverted “Y”
|Up to 1.5 inches
|Up to 1.5 inches
|Adult moths color
|Adult moths markings
Understanding the physical characteristics and life cycle of yellow striped armyworms is crucial for effective management of their populations and prevention of crop damage.
Recognizing Armyworm Infestations
Visible Signs on Plants
One clear sign of a yellow striped armyworm infestation is the damage they cause to various plants, especially leaves. These insects can be very destructive as they create ragged holes and chewed edges on leaves of many crops, including corn and tomato plants1. Other possible victims of their attack include flowers, foliage, and even vegetables. Specific signs of infestation include:
- Nibbling on the underside of leaves
- Green, beet, brown or black caterpillars in large numbers2
- Chewed grass blades and crop damage in gardens and fields
Periods of Activity
The life cycle of yellow-striped armyworm3 plays a huge role in determining the periods of activity:
Understanding these periods of activity can help determine the best times to get rid of armyworms in an infested area.
Natural Control Methods
Predators and Beneficial Insects
There are several natural predators that help control yellow striped armyworms, including:
- Ground beetles
- Beneficial nematodes
- Trichogramma wasps
Attracting these beneficial species to your garden can be done by planting their preferred host plants and creating a hospitable environment.
Using Neem Oil
Neem oil is an effective, organic way to control yellow striped armyworms. To use neem oil:
- Mix 1-2 tablespoons of neem oil with 1 quart of water and a few drops of liquid soap.
- Spray the mixture on affected plants during early morning or late evening.
- Organic and eco-friendly.
- Non-toxic to beneficial insects, birds, and pets.
- Requires multiple applications.
- May take time to show results.
Another option for controlling yellow striped armyworms is manual removal. Follow these steps:
- Inspect your plants during early morning or late evening, when the pests are most active.
- Hand-pick any armyworms you find.
- Drop the pests into a bucket of soapy water.
This method is best suited for small infestations and may require constant vigilance during peak seasons, such as May, July, and August.
Insecticides and Chemical Treatments
Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium. It is effective in controlling yellow striped armyworms as it produces toxins that target the pests’ larvae. Some benefits of using Bt include:
- It is safe for beneficial insects, mammals, and humans
- It is biodegradable and does not persist in the environment
However, one downside is its reduced effectiveness under direct sunlight.
Spinosad is another natural insecticide, derived from soil bacteria. It is quite efficient in controlling yellow striped armyworms, as it targets the nervous system of these pests. Some favorable aspects of using Spinosad are:
- Low toxicity to mammals and beneficial insects
- Rapid degradation in sunlight, preventing long-term toxicity
But, it is toxic to bees and should be applied when they are not actively foraging.
Pyrethrin is a group of organic compounds derived from chrysanthemum flowers. It targets the insect’s nervous system and is effective in controlling the yellow striped armyworm. The benefits include:
- Fast-acting and offers a quick knockdown effect
- Low persistence in the environment
However, it may be toxic to aquatic life and can harm beneficial insects.
Diatomaceous earth is a natural, non-toxic alternative made from crushed fossils of aquatic organisms. It physically damages the exoskeleton of insects, including yellow striped armyworms. Some notable features include:
- Safe for humans, pets, and beneficial insects
- Suitable for both indoor and outdoor applications
Just be aware, its effectiveness diminishes when wet.
Bifenthrin is a synthetic pyrethroid insecticide that is effective against several pests, including the yellow striped armyworm. A few advantages of using Bifenthrin are:
- Provides residual control, lasting for weeks
- Effective against a broad spectrum of insects
However, it might be toxic to aquatic life and has a higher chance of resistance development in insects.
|Adult and Larvae
|Adult and Larvae
|Adult and Larvae
Preventing Future Infestations
Cultural practices play a vital role in minimizing yellow striped armyworm infestations. To prevent them, avoid creating environments conducive to their growth. For example:
- Maintain a healthy lawn, as it can help to resist armyworms
- Limit the use of shade, as they prefer shady spots
- Ensure proper lawn care to discourage overwintering
Removing their preferred food sources, like turfgrass, also helps keep their population in check.
Monitoring and Trapping
Regular monitoring increases the chances of detecting yellow striped armyworms early. Use traps to catch adult moths during summer and early fall, as they are active during this time. Here are some tips:
- Place traps between March and October
- Install them near clusters of plants
Remember, armyworms are more active during early morning and late afternoon. Focus on monitoring during these times.
Choosing Resistant Plant Varieties
Opt for plant species resistant to armyworms, especially in areas around the Rocky Mountains where infestations are prevalent. Some armyworm-resistant plants include:
- Plant A
- Plant B
- Plant C
Pros and Cons of Resistant Plants
|Less vulnerable to armyworms
|Limited variety of plant types
|Reduced need for pest control
|May not be suitable for all gardens
By employing cultural practices, monitoring and trapping, and introducing resistant plant varieties, you can significantly reduce the risk of yellow striped armyworm infestations. Remember, prevention is always better than cure.
In summary, dealing with yellow striped armyworms can be managed using various methods. Outlined below are a few key takeaways.
- Monitor: Regularly check your plants for signs of infestation, especially during early morning or late evening when they are most active1.
- Cultural practices: Maintain a clean environment by removing weeds and crop debris. This helps to reduce breeding sites for the pests.
- Natural predators: Introduce beneficial insects like ladybugs and parasitic wasps that can help control armyworm populations.
Here is a quick comparison table highlighting the pros and cons of using chemical and non-chemical treatments:
|– Fast acting
|– Can harm beneficial insects and the environment
|– Effective control of large infestations
|– Potential for pests to develop resistance
|– Environmentally friendly
|– May take longer to see results
|– Encourages natural predators
|– May not be as effective for large infestations
To effectively deal with yellow striped armyworms, it is important to implement an integrated pest management strategy. This includes monitoring, using cultural practices, and introducing natural predators. Be sure to evaluate the pros and cons of chemical and non-chemical treatments to make an informed decision.
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 – Yellow Striped Armyworms on Water Lilies
Subject: Caterpillars on water lilies
Location: Fullerton, CA
August 12, 2014 12:53 pm
For the second year now we have caterpillars in our water lilies. We have a small backyard pond with goldfish and these guys much away at the Lily pads, nothing else. As you can see from the pictures, they come in black and brown. Do caterpillars sunburn? They get almost as large as a monarch caterpillar and have appeared in late summer both years.
Thank you much!
Signature: Southland BugLovers
Dear Southland BugLovers,
We quickly located an image on BugGuide that matches your darker caterpillar and it is identified as a Yellow Striped Armyworm, Spodoptera ornithogalli, and it is feeding on water lilies in San Diego. Other images on BugGuide indicate that this caterpillar is highly variable, hence your lighter caterpillar as is the diet, which is described on BugGuide thus: “Larvae feed on many herbaceous plants, including alfalfa, asparagus, bean, beet, cabbage, clover, corn, cotton, cucumber, grape, grass, jimsonweed, morning glory, onion, pea, peach, peanut, pokeweed, sweet potato, tobacco, tomato, turnip, wheat, watermelon, and wild onion.”