The corn earworm, also known as the cotton bollworm or tomato fruitworm, can be a frustrating pest for home gardeners and commercial growers alike. This crafty caterpillar has a wide host range and can cause substantial damage to corn, tomatoes, cotton, beans, peppers, and many other crops if left unchecked. While earworms may be difficult to control, there are ways to identify, manage, and prevent infestations through an integrated pest management approach.
Identifying the Corn Earworm
The first step in controlling earworms is learning how to accurately identify them. Here are some key identification features of this pest:
- Appearance: Earworms are typically green, brown, or yellow in color with faint white and pink stripes running the length of their bodies. They have a dark head and can reach 1 to 2 inches long when fully grown.
- Damage: Earworms chew into the fruit and ears of plants, leaving behind trails of excrement and damaged kernels. Look for caterpillars inside tomato fruits, pepper pods, corn silk, and other reproductive structures.
- Life Cycle: Earworms overwinter as pupae in the soil and adults emerge in late spring. After mating, females lay eggs on leaves and newly forming fruit structures. Larvae hatch and begin feeding, going through 5-6 instars over 2-3 weeks before dropping to the soil to pupate. There are 2-3 generations per year.
- Time of Year: Earworms are most active during the summer months when susceptible crops are fruiting. However, be on the lookout for them from mid-spring through early fall.
Carefully inspect plants for signs of earworm damage. Targeted monitoring will help detect infestations early when they are easiest to manage.
Earworm Overview: Biology, Behavior, and Damage
Now that you know how to spot corn earworms, let’s take a closer look at what makes these caterpillars so successful – and destructive. Understanding earworm biology and behavior is key to controlling them.
Host Plants
Earworms have an extremely wide host range of over 100 species of wild and cultivated plants. Their favorites include:
- Corn
- Tomatoes
- Cotton
- Peppers
- Green beans
- Lettuce
- Sorghum
They prefer to feed on reproductive structures like corn ears, cotton bolls, bean pods, and tomato fruits. Feeding damage to these structures can be economically devastating for farmers.
Life Cycle
The earworm life cycle consists of four stages: egg, larva, pupa, and adult moth.
- Eggs are laid singly on leaves and newly forming fruit structures. They are round and pale white, about 0.5 mm wide.
- Larvae are light green to brown caterpillars with faint stripes. They grow through 6 instars over 14-21 days, shedding their exoskeleton between each stage. Mature larvae reach 1 to 2 inches long.
- Pupae form in the soil. They are brown and about 14 mm long. Earworms overwinter in the pupal stage up to 30 inches underground.
- Adults are medium brown moths with a wingspan around 1.5 inches. They are active at night, hiding amongst foliage during the day. Adult lifespans range from 7-10 days.
There are 2-3 generations of earworms per year in most regions. The winter is spent in the pupal stage with new adults emerging in spring.
Feeding Habits
Earworm larvae use tiny mandibles to chew into fruits, buds, and other plant structures. They preferentially feed inside reproductive parts, burrowing tunnels and cavities. Feeding damage progresses through four stages:
- Pinhole entry point
- Penetration and cavity formation
- Growth widens cavities
- Excessive rotting once feeding completes
Larvae are voracious eaters. A single earworm can destroy 3-4 flower buds or young tomato fruits within its 2-3 week development. After completing feeding, mature larvae drop to the soil to pupate.
Identification Tips
When scouting for earworms, target your monitoring to flowers, fruit buds, and developing fruits. Key signs include:
- Holes bored into buds, pods, and ears
- Silks chewed back to the tip of corn ears
- Presence of green larvae and black fecal pellets
- Tan colored moths flying at night
Finding earworms early is critical for management. Don’t wait until you see extensive damage.
Impacts and Damage
If left uncontrolled, earworms can cause extensive damage in home gardens and commercial fields alike. Understanding the types of damage they cause will help motivate control efforts.
Yield Losses
Earworms preferentially attack the most marketable plant structures – the fruits and ears. Their feeding and contamination makes these products unsaleable. Just a few earworms can render an entire corn crop unmarketable.
Spoilage and Rot
The holes and entry points created by earworms facilitate decay and rot organisms. They provide the perfect avenue for bacteria and fungi to invade.
Plant Stress
Earworm feeding compromises the health and vigor of plants. It can stunt growth, lower yields, and increase susceptibility to disease. Wounding from earworms is extremely taxing on crops.
Spread of Disease
Earworms don’t just cause direct damage – they also spread plant diseases. As they move from plant to plant, earworms transmit bacterial and viral pathogens on their mouthparts.
Control Challenges
Earworms are difficult to control for several reasons:
- High reproductive rate
- Multiple generations per year
- Wide host range
- Hidden nature inside fruits and ears
- Rapid development time
- Overwintering stage in soil
An integrated approach is required to manage populations.
Garden Control Strategies
Controlling earworms in the home garden takes diligence, but it’s possible with persistence. Here are some of the top methods:
Hand Removal
Picking earworms by hand is one of the most effective and organic control methods. Check plants daily for signs of damage or larvae. Remove and destroy any caterpillars found. Be sure to check in crevices and under bud caps.
Row Covers
Floating row covers provide a physical barrier that prevents earworm moths from laying eggs on plants. Cover crops with fabric row covers early in the season before earworms are active. Make sure to remove covers when flowers start opening to allow pollination.
Trap Cropping
Trap cropping involves planting earworm favorites like corn and cowpeas around the perimeter of your garden to attract and concentrate pests there. This protects your main crops while earworms get trapped on the sacrificial plants.
Biological Control
Natural predators like parasitic wasps, predatory stinkbugs, and braconid flies help control earworm numbers. Attract these beneficials to your garden by providing diverse flowering plants with small blooms. Avoid broad-spectrum insecticides that kill predators.
Bacillus thuringiensis (Bt)
This microbial insecticide contains proteins that are toxic to earworms when eaten, but safe for humans and beneficial insects. It must be reapplied every 5-7 days. Direct sprays at young larvae for best results.
Insect Growth Regulators
IGRs like azadirachtin and diflubenzuron disrupt the molting process, preventing earworm larvae from reaching destructive later instars. Spray flower buds weekly as they develop.
Sanitation
Remove and destroy infested fruits, pods, and plant debris after harvest. Eliminate earworm food sources and overwintering sites. Till garden soil in fall to disrupt pupae.
Commercial Control Methods
In large-scale agricultural settings, earworm management requires a more rigorous approach. Here are some key tactics:
Monitoring
Use pheromone traps to monitor male moth flights and pinpoint peak activity. Target insecticide applications for threshold levels rather than routine calendar sprays.
Resistant Varieties
Plant earworm-resistant crop varieties when available. Certain varieties have physical and chemical traits that deter earworm feeding and egg-laying.
Chemical Control
Commercial insecticides like pyrethroids, spinosyns, diamides and Bt formulas can prevent crop damage if properly timed. Hire licensed pest control professionals for applications.
Mating Disruption
Mating disruption tools like pheromone ties and puffers release synthetic earworm sex pheromones into fields. This confuses males and prevents mating and egg-laying.
Biological Control
Release parasitic wasps such as Trichogramma species into fields for inundative biological control. The tiny wasps parasitize earworm eggs, greatly reducing populations.
Crop Rotation
Rotating crop locations from year to year avoids build-up of earworm populations. Move host crops to different fields each season.
An integrated pest management plan using multiple tactics gives the best protection for commercial crops. Continual monitoring allows for well-timed control responses.
Frequently Asked Questions
What plants do earworms attack?
Earworms have an extremely wide host range but prefer corn, cotton, tomatoes, soybeans, peppers, lettuce, and other vegetables. They feed on buds, fruits, ears, and pods.
How do I know if I have earworms?
Look for caterpillars inside reproductive structures, holes chewed in buds and fruits, damaged kernels, and trails of poop. Target scouting at silks, pods, and developing fruits.
What do earworm moths look like?
Earworm moths are about 1 inch long with a 1.5 inch wingspan. They are light brown with a faint dark spot on each forewing. The hindwing is paler with a dark border. They are active at night.
Can earworms destroy a crop?
Yes, just a few earworms are capable of causing substantial losses in fruits and ears. Their feeding damage renders produce unmarketable. Entire fields of corn, cotton, or tomatoes can be devastated.
How do earworms overwinter?
Earworms overwinter as pupae up to 30 inches underground. The pupal stage is the overwintering stage in their lifecycle. Adults emerge in spring to start a new generation.
When are earworms most active?
Earworm populations peak in mid to late summer when host plants are flowering and fruiting. However, be on the lookout for them anytime between spring and fall.
How can I naturally control earworms?
Hand removal, row covers, trap cropping, biological control, Bt sprays, and insect growth regulators are organic-approved options for earworm management. Good sanitation also helps.
What insecticides kill earworms?
Pyrethroids, spinosyns, diamides, and Bt insecticides are effective chemical control options. However, make sure to rotate modes of action to avoid resistance.
Conclusion
The voracious corn earworm can quickly devastate backyard gardens and commercial fields alike if left unchecked. Identifying and monitoring for this pest early is critical. Integrated management combining multiple tactics gives the best control and prevents the development of insecticide resistance. Persistence is key, as earworms have multiple generations per year. But with diligent scouting and a proactive pest management approach, gardeners can protect their crops from earworm damage.