Cockroaches, which are actually the larvae of Scarabaeoidea beetles from the order Coleoptera, have become a serious problem in grasslands since 1995. They have been found to infest Zoysia japonica (commonly known as Taiwan grass) and Lyppa macrophylla (carpet grass), with damage becoming more severe in certain areas. These infestations have persisted year after year, causing increasing harm to the grasslands. As a result, cockroaches have now emerged as one of the most significant pests affecting turfgrass.
**First, Understanding Their Habits and Infestation Patterns**
Earthworms primarily target the roots of grasses within the top 10 centimeters of the soil surface. In severe cases, they completely destroy the root systems, leading to the death of the grass. Several factors contribute to their infestation:
1. **Soil Texture and Sediment Content**: Earthworms thrive in loose, sandy soils with high sediment content. For example, the Dayeyou grassland in Haixia Park has over 50% sediment, while the severely damaged Nanwan Avenue has up to 60% sand. Such conditions make it easier for earthworms to move and feed.
2. **High Organic Matter Content**: The soil at Nanwan Avenue is sandy but rich in organic matter, which has accumulated over eight years of continuous grass growth. Dead grass roots remain underground, further enriching the soil and providing a food source for earthworms.
3. **Low Soil Moisture**: Reports from garden workers indicate that insufficient watering has worsened the damage caused by earthworms. Dry soil creates an environment where earthworms can multiply unchecked.
4. **Long-Term Grass Growth**: Grasses that have been growing for many years develop thick, dense root systems. Preliminary surveys show that several affected grass species are over four years old, making them more vulnerable to earthworm attacks.
**Second, Control Methods**
**(a) Agricultural Control**
1. **Soil Replacement**: In heavily infested areas, replacing the top 15–20 cm of soil with clay can create an unfavorable environment for earthworms. This method is considered one of the most effective long-term prevention strategies.
2. **Planting Cover Crops**: Using ramie or other suitable plants along roadsides and wastelands can help suppress earthworm populations by poisoning their adults.
3. **Manual Removal**: Adults can be manually collected by shaking trees or using traps to reduce their numbers.
**(b) Physical Control**
Using black light or dual-color lamps (half black light and half green light) can attract and trap adult earthworms due to their phototactic behavior.
**(c) Chemical Control**
Chemical treatments are currently the primary method for controlling earthworm infestations:
1. Apply 3% carbofuran mixed with 30–50 pounds of sand per acre, allowing the solution to penetrate the soil and contact the pests.
2. Use 3% methyl iso-phosphorus granules, mixed with sand and water, for effective application.
3. Apply 6% BHC (666) at 2–3 pounds per acre, mixed with sand and water.
4. Spray 50% phoxim EC diluted 10 times, mixed with fine sand, and apply evenly across the area.
**(d) Biological Control**
Biological methods are increasingly being used as part of integrated pest management:
1. Fungal agents like *Beauveria tenella* and bacteria such as *Lactobacillus* (e.g., "Doom" and "Japedemic" in the U.S.) can effectively control earthworms.
2. Insecticidal nematodes (*Steinernema* spp.) are also used to infect and kill earthworms.
3. Introducing natural predators like bumblebees or specific parasitic wasps (e.g., *Prosenasiberita Fabricius*) can help manage populations without chemical intervention.
By combining these approaches, it's possible to achieve sustainable and effective control of earthworm infestations in grasslands.
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