How to Control Stevia Blight
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Spot blotch is one of the most significant diseases 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, which gradually expand into irregular or nearly circular lesions. As the disease progresses, dark spots multiply, and the infection spreads upward, eventually causing premature leaf drop.
**Key Characteristics of the Disease**
First, the disease is widespread, with almost every stevia field experiencing some level of infection. Second, it has a long-lasting impact throughout the entire growth cycle of the plant. During autumn cuttings, pathogens can enter the seedbeds and spread through infected leaves on cutting seedlings. The symptoms are usually mild during cold seasons in winter and spring, but once the weather warms up after planting, the disease becomes active from June to July, reaching its peak during this period. Third, there is variation in disease severity 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. It's also advisable to use disease-free cuttings. When possible, implementing dry crop rotation can help reduce the buildup of pathogens. Second, proper field management is crucial. Deep plowing of the soil, watering around the rhizosphere rather than flooding, and ensuring good ventilation to reduce humidity are all important steps. Infected plants should be removed promptly to prevent further spread. Third, chemical control can be effective when conditions are favorable. Fungicides should be applied in advance when the climate is suitable, and continuous treatment should be carried out in fields where the disease first appears. Some stevia varieties are sensitive to certain chemicals like mancozeb and thiophanate-methyl, so it's important to conduct small-scale trials before applying them widely to ensure safety.