Guest Author: Ashley Best
(University of Georgia Cooperative Extension | Newton County, County Extension Coordinator | Agriculture and Natural Resources Agent)
Fall armyworms are a persistent threat to horse pastures in Georgia, particularly from July until the first frost. These destructive pests can devastate pastures quickly, but a proactive, integrated approach can help prevent and control infestations effectively.
Cultural and Mechanical Prevention Methods
Scout and Monitor Regularly
Regular scouting is the cornerstone of armyworm management. Infestations can emerge rapidly, so inspect pastures weekly during summer and fall. Look for signs like skeletonized grass blades, brown patches, or the caterpillars themselves. Scout in the early morning or late evening when armyworms are most active.
Soapy Water Test
For early detection, use a simple soapy water test. Insert a section of PVC pipe or a gallon can (with both ends removed) into the soil and fill it with soapy water. Armyworms hiding in the thatch will float to the surface within minutes. If you find more than 2–3 caterpillars per square foot, consider implementing control measures.
Mowing and Grazing Management
- Mowing: Maintain proper mowing height to deter moths from laying eggs. If an infestation is detected near harvest time, mowing and baling hay can remove a significant portion of caterpillars.
- Grazing: Rotate pastures and avoid overgrazing to promote healthy, dense grass that is more resilient to armyworm damage and recovers faster. Rest severely damaged pastures to encourage regrowth.
Biological Control
Encourage Natural Predators
Natural predators like birds and beneficial insects can significantly reduce armyworm populations. You may notice flocks of birds feeding in infested pastures, a sign they’re helping control the pests.
Use Bacillus thuringiensis (Bt)
Bt, a naturally occurring bacterium, is a safe and effective organic control option. When ingested by armyworms, Bt disrupts their digestive system, causing them to stop feeding and die. It works best on smaller, younger caterpillars and is safe for horses and other animals.
Chemical Control
For severe infestations, chemical treatments may be necessary. Always choose products labeled for horse pastures and follow instructions, particularly pre-grazing and pre-harvest intervals, to ensure safety for horses.
Organic/Lower-Risk Insecticides
- Spinosad: Derived from a soil bacterium, spinosad is effective against young caterpillars and often has a short grazing restriction (typically until the spray dries), making it ideal for horse pastures.
Synthetic Insecticides
Several synthetic pyrethroid insecticides are effective but may require a pesticide applicator’s license. Always check the product label for specific details.
- Chlorantraniliprole (e.g., Coragen, Prevathon): Highly effective with long residual activity and often no grazing restrictions, making it a top choice for horse pastures.
- Zeta-cypermethrin, Beta-cyfluthrin, Lambda-cyhalothrin (e.g., Mustang Maxx, Baythroid, Warrior): These fast-acting pyrethroids typically have a zero-day grazing interval but shorter residual effects.
- Carbaryl (e.g., Sevin): Effective but less practical due to a longer pre-grazing interval (typically 14 days).
Key Considerations for Chemical Applications
- Timing: Apply insecticides in the early morning or late evening when armyworms are actively feeding.
- Water Volume: Use sufficient water to ensure the spray penetrates the grass canopy where armyworms feed.
- Read the Label: The label is the law. Confirm the product is approved for your forage type and follow all application rates, safety precautions, and grazing/harvest intervals.
- Consult Experts: For tailored, up-to-date recommendations, refer to the Georgia Pest Management Handbook or contact your local University of Georgia Extension agent.