In recent months, a significant number of tomato plants in greenhouses across Guangrao, Shandong Province, have been affected by a condition commonly referred to as "fish eye disease." This fungal infection has raised concerns among local farmers due to its rapid spread and impact on crop yield. The disease primarily affects the leaves and stems, though it can occasionally damage the fruits as well.
The initial symptoms appear on the lower leaves, where small, water-soaked spots develop. These lesions gradually expand, forming irregular, grayish-brown, or dark brown patches that resemble the shape of a fish. Small black dots may also be visible on the leaf surface. As the infection progresses, similar symptoms can appear on the stems and fruits, causing further damage to the plant.
This disease is caused by a fungal pathogen, and its development is strongly influenced by environmental conditions. High temperatures and humidity, especially when combined with prolonged rainy weather, create ideal conditions for the disease to thrive. Additionally, factors such as poor crop rotation, insufficient fertilization, continuous planting of the same crop, and inadequate drainage can worsen the situation. This year, the unusually cloudy weather during spring and summer has led to higher humidity levels, contributing to an increased incidence of the disease.
To manage this issue effectively, several control measures are recommended:
1. **Seed Treatment**: Use disease-free seeds and soak them in warm water at 50°C before germination to eliminate any potential pathogens.
2. **Crop Rotation**: Implement a 3–4 year rotation cycle with non-solanaceae crops to reduce the buildup of the fungus in the soil.
3. **Field Management**: Keep the fields clean to minimize disease sources. Practice proper irrigation to avoid excessive moisture, and maintain good air circulation by managing plant density. Apply adequate amounts of phosphorus and potassium to enhance the plant's resistance.
4. **Chemical Control**: At the early stage of infection, apply fungicides such as 50% carbendazim WP diluted at 800–1000 times, 65% dexamethasone WP at 500 times, or 70% thiophanate-methyl WP at 1000 times. Repeat the application every 7 days for 2–3 times.
5. **Growth Regulators**: To further strengthen plant immunity, spray a natural plant growth regulator like Alfalfa Shuofeng 481 every 10–20 days. This helps improve photosynthesis, nutrient absorption, and overall plant resilience.
By combining these strategies, farmers can significantly reduce the impact of "fish eye disease" and protect their tomato crops from future outbreaks.
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