According to years of observation and research conducted in the Walnut Garden, two primary pests commonly affect walnut trees during June and July. These pests are the walnut fruit borer and the clouded coniferous bark beetle. Below are detailed descriptions of their symptoms and effective control measures:
**First, the Walnut Fruit Borer**
1. **Symptoms of Damage**: The larvae of the walnut fruit borer bore into the developing nuts, causing internal damage. As a result, the affected fruits darken, shrink, and eventually fall from the tree, leading to significant yield loss. This condition is often referred to as "black walnuts" due to the darkened appearance of the damaged fruit.
2. **Control Measures**:
- **Manual Removal**: Regularly collect and destroy fallen fruits to reduce the number of overwintering larvae.
- **Crown Spraying**: From early June to late July, apply a mixture of 25% diflubenzuron suspension (diluted 1500 times) and 2.5% deltamethrin emulsion (diluted 3000 times). Spray every 10–15 days for two applications, which has shown the best results.
- **Ground Spraying**: In early June, spray 50% phoxim emulsifiable concentrate on the ground around the base of the tree at a dilution of 300–500 times, using approximately 0.5 kg per mu. This helps reduce the survival rate of the next generation of larvae.
**Second, the Clouded Coniferous Bark Beetle**
1. **Symptoms of Damage**: This pest belongs to the longhorn beetle family and is also known as the "walnut big sky" or "iron bark" beetle. The larvae bore into the trunk, disrupting the tree's vascular system, which can lead to stunted growth, poor wood quality, and even tree death in severe cases. These beetles have a life cycle that spans two years, with one generation emerging every three years. Both larvae and adults overwinter inside the tree trunks. The peak larval activity occurs between early July and late July.
2. **Control Measures**:
- **Manual Removal**: Observe the tree trunks regularly for signs of egg-laying tunnels. Use a hard object to crush the eggs or remove the larvae directly. If fresh frass (insect excrement) is found, carefully peel back the bark with a knife to expose and kill the larvae.
- **Light Trapping**: Set up black light traps to attract and capture adult beetles, taking advantage of their phototactic behavior.
- **Chemical Blocking**: When infestation levels are high, systemic insecticides can be applied directly to the affected areas. For example, inject 80% dichlorvos solution (diluted 500 times) into the entry holes or use poisoned sticks soaked in insecticides like deltamethrin. After treatment, seal the holes with mud to prevent re-infestation.
By implementing these integrated pest management strategies, farmers and gardeners can effectively reduce the impact of these pests on walnut crops and maintain the health of their trees.
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