How to Control Stevia Blight

Spot blotch is one of the most significant diseases affecting stevia cultivation. Over the past few years, as planting periods have extended, the disease has become more severe, significantly limiting both the yield and quality of the crop. In the early stages, the disease appears as small brown spots on the leaves, which gradually grow into larger, irregular or nearly circular lesions. As the infection progresses, multiple dark spots develop, and the affected leaves eventually fall off, leading to premature defoliation. One key characteristic of this disease is its widespread occurrence—nearly every stevia field experiences some level of infection. Another is its long-lasting impact, as the disease can affect the plant throughout its entire growth cycle. During autumn cuttings, the pathogen can be introduced into the seedbeds through infected cutting material, and it spreads further via diseased leaves on the seedlings. The symptoms are usually mild during the colder months in winter and spring, but as temperatures rise and rainfall increases, the disease becomes active between June and July, reaching its peak during this period. Additionally, there is variation in the susceptibility of different stevia varieties to the disease. To manage spot blotch effectively, several preventive measures should be taken. First, crop rotation is essential. Seedbeds should be carefully selected to minimize the risk of bacterial spread through contaminated soil, and disease-free cuttings should be used whenever possible. When feasible, implementing a dry crop rotation system can help reduce the buildup of pathogens. Second, proper field management plays a crucial role. Soil should be deeply tilled, watering should focus on the rhizosphere rather than flooding the plants, and good ventilation should be maintained to lower humidity. Infected plants must be removed promptly to prevent further spread. Third, chemical control methods may be necessary. Pesticides such as mancozeb and thiophanate-methyl can be effective, but they should be tested on a small scale first to ensure safety for the specific variety being grown. Once confirmed safe, these treatments can be applied consistently in the field when the conditions are favorable for disease development.

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