Pasture Pests

5 Common Pasture Pests affecting New Zealand Crops

If you've observed a decline in pasture productivity, such as the appearance of brown or dead patches, dead or dying tillers, poor or patchy seed germination, it's possible that pasture pests could be causing the issue. Conducting regular inspections of your pasture, especially during peak pest activity or vulnerable periods such as after rainfall, rain after a long dry spell or just during the growing season, can aid in early detection of infestation signs. In this guide, we've identified five prevalent pasture pests in New Zealand, provided guidance on recognizing them, and suggested methods for their control

1. Grass Grub (GG):

Identification: Grass Grub larvae are creamy-white, C-shaped insects with brown heads, typically found underground in soil. 

Impact: Grass Grubs are voracious feeders on grass roots, leading to reduced pasture productivity and compromised soil structure. They particularly favor young grass, causing significant damage to newly sown pastures. You may be able to see the following effects in your pasture:

• Irregular patches of dying or yellowing grass.

• Presence of birds, such as starlings or magpies, actively foraging in affected areas, as they often feed on grass grubs.

• Digging into the soil may reveal white, C-shaped larvae underneath.

Control: Control measures often include biological control agents, such as nematodes or Beauveria Bassiana fungi, as well as chemical treatments. However, the efficacy of chemical control can diminish over time due to the development of resistance. There are a number of options for treatment, talk to your farm adviser or give us a call to discuss further.

2. Argentine Stem Weevil (ASW):

Identification: Adult Argentine Stem Weevils are small beetles with distinctive elongated snouts, while their larvae are legless, white grubs found within grass stems.

Impact: ASW larvae tunnel into grass stems, causing characteristic "dead-heart" damage, which stunts growth and reduces pasture quality. This pest is particularly problematic in regions with mild temperatures and higher rainfall. You may be able to see the following effects in your pasture:

• "Dead-heart" symptoms, characterized by the center of grass tillers turning brown or dying.

• Notching or chewing damage on grass leaves and stems.

• Presence of adult weevils on pasture vegetation, particularly during early morning or late afternoon.

Control: Integrated pest management strategies, combining cultural practices like pasture rotation with targeted insecticide applications, are commonly used to manage Argentine Stem Weevil populations. There are a number of options for treatment, talk to your farm adviser or give us a call to discuss further.

3. Black Beetle (BB):

Identification: Black Beetles are shiny, black insects with robust bodies, typically found in soil and thatch layers.

Impact: Both adult and larval stages of Black Beetles feed on grass roots, leading to reduced pasture vigor and increased susceptibility to drought stress. Infestations can result in patches of dead or dying grass. You may be able to see the following effects in your pasture:

• Patches of dead or dying grass, often expanding over time.

• Presence of adult beetles on pasture surfaces, especially during warm evenings or after rainfall.

• Undermined grass roots visible upon closer inspection.

Control: Cultural practices such as pasture renovation and drainage improvements, coupled with chemical control options, are employed to manage Black Beetle populations. There are a number of options for treatment, talk to your farm adviser or give us a call to discuss further.

4. Crickets:

Identification: Crickets are nocturnal insects with long antennae and powerful hind legs for jumping.

Impact: While not as destructive as some other pests on this list, crickets can still cause significant damage to pastures by feeding on young seedlings and grass blades. Their presence can lead to reduced pasture density and vigor. You may be able to see the following effects in your pasture:

• Notched or ragged edges on grass leaves.

• Presence of crickets during nighttime hours, as they are nocturnal feeders.

• Audible chirping or clicking sounds, particularly in the evening.

Control: Cultural methods such as maintaining proper pasture health and diversity can help reduce cricket populations. In severe cases, chemical control measures may be necessary. There are a number of options for treatment, talk to your farm adviser or give us a call to discuss further.

5. Slugs:

Identification: Slugs are soft-bodied, slimy mollusks without shells, typically found in moist environments.

Impact: Slugs feed on both living and decaying plant material, including grass seedlings and foliage. Their feeding activity can cause extensive damage to pastures, especially in wet and humid conditions. You may be able to see the following effects in your pasture:

• Slimy trails or mucus trails left behind on grass blades or soil surfaces.

• Irregular feeding damage on grass seedlings, with chewed edges or holes.

• Presence of slugs during damp or humid conditions, especially in the evening or early morning.

Control: Control of slugs often involves habitat modification to reduce moisture levels and the use of baits. Additionally, cultural practices like timely grazing management can help minimize slug damage. There are a number of options for treatment, talk to your farm adviser or give us a call to discuss further.

If you think you may have a problem with pasture pests and want some expert advice, get in touch with us.