Authors: Brittany Justesen & Jessica Sullivan, UF IFAS Extension – Osceola County
Armyworms are highly destructive caterpillars that primarily feed on grasses, making them a significant concern for cattle ranchers. Several species of moth caterpillars in Florida are known as “armyworms”: Fall Armyworm (Spodoptera frugiperda), Southern Armyworm (Spodoptera eridania), and Beet Armyworm (Spodoptera exigua). These species may occur together, and all may have multiple generations per year.
Identification
Life Stages
- Larvae (Caterpillar Stage):
- Color: Green to brown, often with dark stripes.
- Size: Up to 1.5 inches long.
- Distinctive Features: Inverted “Y” shape on the head.
- Adult Moths:
- Color: Brown with a wingspan of about 1.5 inches.
- Distinctive Features: Dark stripe on forewings.
- Eggs: Adults moths can lay up to 1500 eggs during lifespan of a few weeks.
When to Scout for Fall Armyworms
Best Times to Scout
- Late Summer to Early Fall (August-October): Peak activity typically occurs after heavy rains or storms.
- New Growth: Scout areas with lush, green grass, as these are most attractive to armyworms.
Tips for Effective Scouting
- Inspect fields weekly during high-risk periods.
- Look for signs of feeding damage or caterpillars themselves. The last 2-3 days of the caterpillar stage, 80% of leaf consumption occurs causing quick pastures destruction.
- Scout in the early morning and late afternoon when armyworms are most active
- Waiting for signs of birds in a pasture could be too late to avoid damage
Symptoms to Look for in Pastures
Signs of Infestation
- Leaf Damage: Irregular holes in leaves, starting from tips and edges.
- Wilting or Browning: In serve cases, pastures may appear wilted and turn brown.
- Frass: Greenish-black droppings found on the ground.
- Patchy Areas: Infestations can create uneven growth patterns in the pasture.
Preferred Grass Types
Armyworms prefer well fertilized grasses and may feed on a variety of forages, causing severe damage to pastures and hayfields. Armyworms can infest hundreds of plant species, including the following forages:
Bermudagrass (Cynodon dactylon)
Limpograss (Hemarthria altissima)
Bahiagrass (Paspalum stelatum)
Aeschynomene (Aeschynomene americana)
Rhizoma perennial peanut (Arachis glabrata)
Sunn hemp (Crotalaria juncea)
Sorghum (Sorghum bicolor [L.] Moench)
Annual ryegrass (Lolium perenne L. ssp. Multiflorum) and other cool-season forages
Control Options for Fall Armyworms in Pastures
Management Strategies
- Cultural Practices:
- Mowing/Grazing: Mowing or grazing can reduce feeding sites for caterpillars.
- Cutting Hay: Cutting hay can help protect your crops and reduce the need for chemical controls.
- Biological Control:
- Encourage natural predators like birds and beneficial insects.
- Chemical Control:
- Integrated Pest Management (IPM): Combine methods for effective control while minimizing chemical use.
- Insecticides: Use targeted insecticides and consider mixing (e.g., pyrethroids are fast acting and diflubenzuron products provide residual control). If rain is in the forecast, consider a rainfast product like Vantacor, Shenzi, or Besiege. Always read the label first before purchasing and applying to be sure the product is labeled for intended use and forage crop. To ensure caterpillars and insecticide contact, applications should be made in the morning or evening. Always follow all PPE (Personal Protection Equipment) guidelines when applying insecticides.
| Insecticides available to control armyworms in Florida grass pastures and hayfields | ||||||
| Insecticide Class / Mode of Action (MOA) Group |
Active Ingredients | Trade Names | Restricted Use Pesticide (Requires Pesticide Applicator License to purchase or apply) |
Pre-grazing interval (days) | Pre-harvest interval for hay (days) |
Residual activity/Rainfast |
| Pyrethroid 3A |
Cyfluthrin | Tombstone | Restricted Use | 0 | 0 | 3-5 days |
| Beta-cyfluthrin | Baythroid XL, Sultrus | Restricted Use | 0 | 0 | 3-5 days | |
| Zeta-cypermethrin | Mustang, Mustang Maxx | Restricted Use | When dry | 0 | 3-5 days | |
| Lambda-cyhalothrin | Kendo 22.8 CS, Drexel L-C Insecticide, Lamcap II, Paradigm VC, Province II, Ravage, Silencer, Warrior II with Zeon Technology | Restricted Use | 0 | 7 for hay (0 for cut forage) |
3-5 days | |
| Benzoylurea 15 |
Diflubenzuron | Durant 2 L IGR, Unforgiven, Dimilin, Micromite | Restricted Use | 0 | 1 | 7-14 days |
| Methoxyfenozide | Intrepid 2F, Invertid 2F, Troubadour 2F, Zylo Insecticide | 0 | 7 days for hay (0 for cut forage) |
7 -14days | ||
| Diamide 28 |
Chlorantraniliprole | Vantacor Insect Control, Coragen, Shenzi 400SC | 4 hours | 0 | 14-20days /Yes rainfast | |
| Spinosyn 5 |
Spinosad | Blackhawk | When dry | 3 | 4-7days | |
| Diamide 28 + Pyrethroid 3A |
Chlorantraniliprole + Lambda-cyhalothrin | Besiege | Restricted Use | 0 | 7 for hay (0 for cut forage) |
14-20 days/Yes rainfast |
| Carbamate 1A |
Methomyl | Lannate, Nudrin | Restricted Use | 7 | 3 (7 for cut forage) |
4-7 days |
Monitoring and Thresholds
- Regularly monitor pastures and consider treatment if more than 3 caterpillars are found per square foot.
Conclusion
Armyworms can significantly impact the health of your pastures and hayfields. By recognizing the signs of infestation early, understanding their preferred grass types, and implementing effective control strategies, you can protect your pastures from these damaging pests. Stay proactive and keep your pastures thriving! For additional questions or concerns, please contact your county extension agent.
Fall Armyworm Control in Pastures (agrilife.org)
Fall Armyworms in Hayfields and Pastures (msstate.edu)
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