In recent weeks, a significant number of tomato plants in greenhouses across Guangrao, Shandong Province, have been affected by a fungal disease commonly referred to as "fish eye disease" by local farmers. This condition primarily targets the leaves and stems of the plants, though it can occasionally affect the fruit as well.
The symptoms typically begin on the lower leaves, gradually spreading upward. Initially, small, water-soaked spots appear, which then expand into gray, brown, or dark brown polygonal lesions that resemble fish-like shapes. Small black dots may also be visible on the leaf surface. The stems and fruits may develop similar brown spots, further reducing the quality and yield of the crop.
This disease is caused by a fungal pathogen, and its development is strongly influenced by environmental conditions. High temperatures combined with high humidity create ideal conditions for the fungus to thrive. At 25°C, especially during prolonged rainy periods, the disease spreads rapidly. Additionally, poor agricultural practices such as excessive planting density, insufficient fertilization, continuous cropping without crop rotation, and poor drainage can worsen the situation. This year, the unusually cloudy weather during spring and summer has led to higher humidity levels, resulting in a more severe outbreak.
To manage this issue, several effective control measures can be implemented:
1. **Seed Treatment**: Use disease-free seeds and soak them in warm water at 50°C before germination to eliminate any potential fungal contamination.
2. **Crop Rotation**: Implement a 3–4 year rotation cycle with non-solanaceae crops to break the disease cycle and reduce pathogen buildup in the soil.
3. **Field Management**: Keep the greenhouse clean and remove infected plant debris to minimize disease sources. Practice proper irrigation to avoid excess moisture, and ensure good air circulation by maintaining appropriate planting density. Applying adequate phosphorus and potassium fertilizers can enhance the plant's natural resistance.
4. **Chemical Control**: Early intervention is crucial. Apply fungicides such as 50% carbendazim wettable powder diluted at 800–1000 times, or 65% mancozeb wettable powder at 500 times, or 70% thiophanate-methyl wettable powder at 1000 times. Repeat the application every 7 days for 2–3 times, depending on the severity of the infection.
5. **Biostimulants**: To further strengthen plant health, spray a natural plant growth regulator like Alfalfa Shuofeng 481 every 10–20 days. This helps promote photosynthesis, improve nutrient uptake, and boost the plant’s ability to resist diseases.
By combining these strategies, farmers can effectively manage "fish eye disease" and protect their tomato crops from significant losses.
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