Spot blotch is the most significant disease affecting stevia cultivation. Over the past few years, as the planting period has extended, the disease has become more severe, posing a serious threat to both the yield and quality of stevia crops. In the early stages of infection, brown spots appear on the leaves of stevia plants. These spots gradually expand into larger, nearly circular lesions, and in later stages, multiple dark spots develop. The disease then spreads upward through the plant, eventually causing premature leaf drop.
**Characteristics of the Disease**
First, the disease is widespread, affecting almost all stevia fields to varying degrees. Second, it has a long-lasting impact cycle, as it can occur throughout the entire growth period of the plant. During autumn cuttings, pathogens can enter the seedbed and spread through infected leaves on the cutting seedlings. The symptoms are usually mild during the cold season in winter and spring, but after planting in spring, with rising temperatures and increased rainfall, the disease becomes active between June and July, reaching its peak during this time. Third, there are differences in susceptibility among different stevia varieties.
**Prevention and Control Measures**
To prevent spot blotch in stevia, several strategies can be implemented. First, crop rotation is essential. Seedbeds should be carefully selected to minimize the risk of bacterial spread through soil, and disease-free cuttings should be used whenever possible. If conditions allow, implementing a dry crop rotation system can help reduce the buildup of pathogens. Second, field management plays a crucial role. Deep plowing of the soil, watering around the rhizosphere rather than flooding, and ensuring proper ventilation to reduce humidity are important practices. Diseased plants should be promptly removed to prevent further spread. Third, chemical control methods can be effective when applied correctly. Pesticides should be applied in advance when weather conditions are favorable, and regular monitoring is necessary to detect early signs of infection. Once the disease appears, continuous treatment in the field is required. Some stevia varieties may be sensitive to certain fungicides like mancozeb or thiophanate-methyl, so small-scale testing is recommended before large-scale application to ensure safety and effectiveness.
By combining these preventive and management practices, farmers can significantly reduce the impact of spot blotch and improve the overall health and productivity of their stevia crops.
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