Cutworms are a common pest that attack a wide variety of crops (Photo 1), particularly in the early stages of growth. These soil-dwelling larvae can cause significant damage by cutting through plant stems at or just above the soil surface (Photo 2), leading to plant death.
Photo 1. C- shaped cutworm larva
Photo 2. Growing shoot of pepper plant is cut by cutworm larva
Beneficial Nematodes as a Biological Control Agents
Beneficial nematodes are microscopic, soil-dwelling roundworms that naturally parasitize many insect pests, including cutworms. As part of an integrated pest management approach, the most commonly used beneficial nematodes, including Steinernema carpocapsae (Photo 3) and Heterorhabditis bacteriophora (Photo 4), offer an effective, environmentally friendly control method that is safe for humans, pets, wildlife, and pollinators. Both Steinernema carpocapsae and Heterorhabditis bacteriophora nematodes enter the body cavity of cutworm larvae through natural openings such as the mouth, anus, and breathing pores (Photo 5). Once inside, these nematodes release symbiotic bacteria—Xenorhabdus spp. and Photorhabdus spp., respectively—into the insect's blood. The bacteria multiply, causing septicemia and killing the larvae within 48 hours (Photo 6 and 7). The nematodes then reproduce within the cadaver for approximately 12 days or until food (growing bacteria) becomes scarce. When resources are depleted, they exit as infective juveniles in search of new hosts, continuing their life cycle (Photo 3 and 4).
Photo 3. Steinernema carpocapsae Nematodes
Photo 4. Heterorhabditis bacteriophora nematodes
Photo 5. Nematodes enter into the body cavity of nematodes through natural openings like mouth, anus and breathing pores.
Photo 6. Larval cadavers were infected with Steinernematid nematodes.
Photo 7. Larval cadavers were infected with Heterorhabditid nematodes.
Benefits of Using Beneficial Nematodes
Targeted Action: Nematodes selectively attack pests like cutworms, leaving beneficial insects unharmed. Environmentally Safe: Unlike chemical pesticides, nematodes pose no risk to humans, animals, or ecosystems. Reduced Resistance Development: Pests are less likely to develop resistance to biological agents than to synthetic chemicals. Ease of Application: Nematodes can be easily applied using a watering can or sprayer and are available in liquid or granular forms. Sustainability: They support an eco-friendly approach to pest management.
Applying Nematodes for Cutworm Control
To maximize nematode effectiveness, follow these guidelines:
Timing and Quantity: For effective cutworm control, apply 25,000 nematodes per square foot when cutworm larvae are actively feeding, typically in late spring or early summer. Applying in the early morning or evening helps protect nematodes from UV exposure, which can kill them instantly.
Soil Moisture: Ensure the soil is moist before and after application to help nematodes move through the soil and effectively locate and infect host larvae, grubs, or caterpillars.
Temperature: Nematodes thrive in temperatures between 50°F and 85°F (10°C to 29°C).
Application Method: Use a sprayer, watering can, or spreader for even distribution.
Challenges and Considerations
Soil Conditions: Nematodes perform best in moist, well-drained soils and may struggle in dry or compacted conditions.
Persistence: They can persist longer in the soil if they have a continuous source of food (hosts) and the presence of optimum moisture and temperature; otherwise, repeated applications may be necessary.
Compatibility: Nematodes work well with other biological controls and many chemical pesticides.
Conclusion
Beneficial nematodes offer a natural, eco-friendly alternative to chemical pesticides for controlling cutworms. Their targeted action, ease of application, and minimal environmental impact make them a valuable tool in sustainable agriculture. Proper timing, environmental conditions, and application techniques are key to their success.