Title: Unraveling the Culprits: Grass Grub Larvae and Porina in New Zealand Lawns

Introduction:

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A lush, vibrant lawn is the dream of many homeowners in New Zealand. However, this idyllic vision can be challenged by two formidable foes - the grass grub larvae (Costelytra zealandica) and the porina caterpillars (Wiseana spp.). These pests are common and notorious for causing damage to lawns and grasslands across the country. In this article, we will explore both species, learn how to identify them, and discuss effective methods to manage their impact on your outdoor space.

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1. Grass Grub Larvae (Costelytra zealandica):

Grass grub larvae, scientifically known as Costelytra zealandica, are the immature stage of the brown beetle. These C-shaped larvae possess six prominent legs near their head and can grow up to 25mm long. They have a voracious appetite for grass roots, causing irregular patches of brown or dying grass on lawns, golf courses, and pasture lands. Grass grub larvae are most active during the warmer months, making vigilance during this period crucial for early detection and control.

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2. Porina Caterpillars (Wiseana spp.):

Porina caterpillars, encompassing species like Wiseana copularis and Wiseana cervinata, are night-feeding moths found in New Zealand. These caterpillars have smooth bodies and vary in appearance, often exhibiting green or brown colors with distinctive markings. During their larval stage, porina caterpillars feed on grass and pasture foliage, posing a significant threat to the health of lawns and grazing areas.

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3. Signs of Infestation:

Detecting these pests early is vital in curbing their detrimental impact on your lawn:

a. Grass Grub Larvae:
   - Brown Patches: Irregular brown or yellowish patches scattered across the lawn due to root feeding.
   - Loose Turf: Weak and loose turf that can be easily lifted or rolled back.
   - Increased Bird Activity: A surge in bird activity, especially starlings and blackbirds, as they feed on the grubs.

b. Porina Caterpillars:
   - Grazing Damage: Visible grazing damage on grass and foliage, often leading to scalloped or notched leaves.
   - Night Feeding: Caterpillars are nocturnal feeders, so you may not spot them during the day.
   - Presence of Moths: Moths flying around your lawn during the night can indicate the presence of porina caterpillars.

 

4. Prevention and Management:

To safeguard your lawn from both grass grub larvae and porina caterpillars, consider these preventive and control measures:

a. Regular Lawn Maintenance: Maintain a healthy lawn through regular mowing, watering, and fertilization practices to reduce vulnerability to pests.

b. Biological Controls: Consider introducing beneficial nematodes to target grass grubs or natural predators like birds that feed on caterpillars.

c. Chemical Treatments: In severe infestations, utilize insecticides labeled for specific pest control. Always follow instructions carefully to minimize environmental impact.

d. Night Vigilance: To manage porina caterpillars, consider inspecting your lawn during the night with a flashlight to spot caterpillar activity.

Conclusion:

Grass grub larvae and porina caterpillars are two significant lawn pests that can mar the beauty of your outdoor space in New Zealand. By understanding their characteristics and behavior, you can take appropriate measures for early detection and effective management. Whether you're dealing with the root-feeding grass grub larvae or the night-feeding porina caterpillars, a combination of preventive practices and targeted interventions will help you maintain a lush, green lawn that stands resilient against these troublesome pests. If in doubt, seek guidance from local pest control experts or agricultural extension offices to ensure optimal pest management.

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Further reading:
https://www.daltons.co.nz/gardening-guides/controlling-porina-caterpillars-lawns#:~:text=Porina%20moth%20caterpillars%20feed%20on,bare%20patches%20in%20the%20lawn.
https://www.kiwicare.co.nz/problem/porina/

https://plantdoctor.co.nz/problem-finder/porina-caterpillar/