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, significantly limiting both the yield and quality of stevia crops. In the early stages, brown spots appear on the leaves, which gradually expand into irregular or nearly circular lesions. As the disease progresses, multiple dark spots develop, and the infection spreads upward, causing premature leaf drop.
**Characteristics of the Disease**
First, the disease is widespread, with nearly all stevia fields showing 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 cutting leaves. The symptoms are usually mild during the cold seasons in winter and spring, but as temperatures rise and rainfall increases after planting in spring, the disease becomes active between June and July, reaching its peak during this period. Third, there are differences in susceptibility among different stevia varieties, making some more prone to infection than others.
**Prevention and Control Measures**
To prevent stevia spot blotch, several strategies should 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. When conditions allow, dry crop rotation can help reduce disease buildup. Second, field management plays a crucial role. Deep plowing of the soil, watering around the rhizosphere rather than flooding, ensuring good ventilation, reducing humidity, and promptly removing diseased plants are all important steps. Third, chemical control is often necessary. When environmental conditions are favorable for the disease, preventive pesticide applications should be carried out in advance. If infections are detected, continuous treatment in the field is recommended. Some stevia varieties are sensitive to certain fungicides such as mancozeb and thiophanate-methyl, so a small-scale test should always be conducted first to ensure safety before large-scale use.
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