Managing Porina in Pasture: Effective Control Methods and Strategies for Recovery
Porina Caterpillars
A serious pest in New Zealand’s pasture-based farming systems.
Photo credit to: https://teara.govt.nz/
Porina caterpillars (Wiseana spp.) are a serious pest in New Zealand’s pasture-based farming systems. These nocturnal larvae feed on the leaves and roots of pasture plants, particularly in autumn and winter, leading to significant pasture thinning, lower feed availability, and reduced livestock performance.
Effective Porina control requires an integrated approach that combines chemical sprays, biological treatments, and strategic pasture renovation. Here’s how to tackle Porina infestations and restore pasture health.
In spring and summer Adult moths fly mainly in October-January, and do not feed, moths can lay up to 3000 eggs in a lifecycle. The eggs hatch into caterpillars in 10 to 21 days. The Porina caterpillars live in vertical burrows and are 15 mm to over 50 mm long, dark greenish-grey on top and cream underneath. They feed above the ground on leaves from late evening and leave worm-like, granular casts. Patches of shorter pasture, with increasing areas of bare ground, indicate porina damage.
Porina caterpillars damage pasture in late autumn and throughout winter as growth slows. Caterpillars are greyish yellow with a dark brown head, and grow up to 6 cm in length. They live in tunnels in the soil, emerging at night to feed on the surface, grazing grass and clover. Their tunnels are associated with bare patches of pasture, and dead plants. Tunnel entrances can be found as holes, covered in soil castings and debris held together with silken threads.
The Damage Caused by Porina Caterpillars
Porina caterpillars live in burrows in the soil and emerge at night to feed on pasture foliage. As they grow, they consume more plant material, creating bare patches and weakening pasture persistence.
Common signs of Porina include:
🟠 Loss of pasture cover, increasing vulnerability to weed invasion, and soil erosion
🟠 Reduced feed availability in winter and early spring
🟠 Timing of control measures can be determined from the times moths fly. These vary between regions and sometimes within localities. Learn to recognise porina moths and note when they fly in your area.
🟠 Long-term degradation requiring costly pasture renovation or reseeding
🟠 Check out any suspect paddocks in late summer or early autumn, by digging squares out of the ground 300mm deep. 5-6 grubs per 20 cm square and there’s likely to be a problem
Early detection and timely intervention are key to minimizing the economic and environmental impact of these pests.
Chemical Control: Targeted Insecticide Applications
One of the most effective methods for Porina treatment is the use of targeted insecticides like Diflubenzuron, an insect growth regulator (IGR). This product disrupts the caterpillar’s moulting process, leading to death before they cause serious damage.
Best practices for chemical Porina control:
✅ Apply Diflubenzuron in autumn when caterpillars are small and actively feeding, An insect growth regulator which disrupts chitin deposition and prevents moulting of porina caterpillar
✅ Diazol® 800 is a high strength, broad spectrum insecticide
✅ Large caterpillars control using chlorpyrifos insecticide
✅ Diazinon granular insecticide for the control of porina caterpillar and grass grub in pasture
✅ Use label-recommended rates to ensure efficacy without harming beneficial insects
✅ Apply using adequate water volumes to ensure soil contact and coverage
Note: Always check the latest product approvals and follow local guidelines for application timing and safety.
Boosting Recovery: Combine Porina Spray with Liquid Nitrogen and PGRs
To get more value from your spray application and aid pasture recovery, consider adding Liquid Nitrogen (N) and Plant Growth Regulators (PGRs) during the same application window.
Benefits of this integrated approach:
🌱 Stimulates rapid regrowth of damaged pastures
🌱 Increases winter and early spring feed availability
🌱 Reduces the need for multiple spray passes, saving time and money
This pasture recovery strategy helps offset the damage caused by Porina and strengthens sward resilience.
Organic Porina Control: Bio-Insecticide
For farmers seeking a sustainable option, there is an organic bio-insecticide that uses natural compounds to target Porina larvae.
Metarhizium Anisopliae fungi is currently being trialled in NZ for control against Porina, Metarhizium anisopliae is the type of fungi, that grows naturally in soils throughout the world and causes disease in various insects by acting as a parasitoid
Advantages of the organic solution:
🐞 Minimal impact on beneficial insects and soil health
🌍 Fits within an Integrated Pest Management (IPM) strategy
🌾 Suitable for organic farms or those transitioning away from synthetic chemicals
While the efficacy may vary depending on infestation levels, it’s a valuable tool in long-term pest management.
Photo credit to: https://teara.govt.nz/
Preventing Future Porina Infestations: Sow Seed with Endophyte Protection
One of the most proactive ways to reduce Porina damage maintain low pasture cover during late spring to reduce survival of eggs and young larvae. Paddocks left for hay or silage, or poorly grazed and rank, are typically worst affected by porina as higher pasture covers help eggs survive.
AR37 provides pastures with a some level of porina control. Initial testing with NEA12 and RGT18 has shown they could also provide a level of control, endophyte pastures will still need to be monitored for porina and sprayed when larval numbers are high
Pasture Species Less Favoured by Porina:
✅ Cocksfoot (Dactylis glomerata) – unpalatable and chemically deterrent
✅ Tall Fescue (with strong endophyte) – texture and chemistry reduce feeding
✅ Chicory and Plantain – bitter compounds deter caterpillars
✅ Endophyte-Enhanced Ryegrasses – produce alkaloids toxic to Porina larvae
Species More Susceptible to Porina:
❌ Traditional ryegrasses without endophytes
❌ White clover – commonly targeted and heavily damaged
❌ Kikuyu – vulnerable in warmer regions
❌ Phalaris – young seedlings especially at risk
By selecting Porina-resistant pasture species and endophyte technologies, farmers can build a more resilient grazing system.
Summary: Key Steps for Managing Porina in Pasture
🔍 Monitor for early signs of Porina activity in autumn
💧 Apply Diflubenzuron or approved insecticides when larvae are small
🧪 Integrate Liquid N and PGRs to stimulate pasture recovery
🍃 Consider organic sprays for sustainable Porina management
🌾 Sow endophyte-protected pasture species for long-term resistance
Final Thoughts
Porina caterpillars present a persistent challenge for New Zealand farmers, but with the right mix of chemical, biological, and cultural controls, you can significantly reduce their impact. A proactive, integrated approach will help you maintain productive pastures, healthier livestock, and lower re-sowing costs year after year.
For advice on selecting the right endophyte seed or tailored Porina control plans for your farm, get in touch today.