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Potato diseases are a major concern for farmers, affecting both the quality and yield of crops. Among these, scab is one of the more common and damaging conditions. Scab typically occurs alongside late blight and manifests as brown spots on the surface of potato tubers. These spots gradually expand into larger, irregularly shaped patches. The affected area becomes corky and rough, with the center either sunken or raised, forming a hard, scab-like lesion. Importantly, the infection remains limited to the outer layer of the skin and does not penetrate deep into the tuber, distinguishing it from whitefly disease.
Scab development is influenced by environmental factors such as temperature (25–30°C) and soil type. Sandy loam soils that are slightly alkaline tend to be more prone to the disease, while acidic soils (pH < 5.2) have lower incidence. Resistant varieties are key in managing scab, with thin-skinned, pale varieties being more vulnerable, while thick-skinned, brown varieties show greater resistance.
To control scab, farmers should select resistant potato varieties, apply well-decomposed organic manure or green manure to suppress disease occurrence, and ensure proper irrigation to avoid drought stress.
Whitefly disease, also known as powdery scab, primarily affects tubers and roots, though stems can also be infected. Early symptoms include small brown spots on the epidermis, surrounded by a translucent yellow halo. Over time, these spots grow into raised, 3–5 mm diameter "freckles," resembling closed crickets. As the disease progresses, the epidermis ruptures, exposing an orange-red subcutaneous layer and releasing dark brown spores. This stage is referred to as the "open cricket" phase. Infected roots develop bean-shaped swellings, which can hinder nutrient uptake.
The disease thrives in moist soils with temperatures between 18–20°C and pH levels ranging from 4.7 to 5.4. The severity of the disease depends largely on initial infections rather than repeated cycles in the field.
Prevention and control measures include using disease-free seed potatoes, proper storage and planting practices, and treating seeds with a 40% formalin solution (200 times diluted) for 5 minutes, followed by a 2-hour covering period before drying and planting. Increasing organic matter and bio-fertilizers, along with applying wood ash, helps adjust soil pH. Avoiding flood irrigation and rotating crops with sorghum can further reduce disease spread.
Virus diseases are another significant threat to potato crops. These diseases often result from poor management practices, such as using contaminated seed potatoes, over-cultivation, and inadequate water and nutrient supply. Symptoms include plant stunting, leaf deformation, and reduced yield. Two common types are mosaic and leaf rolling. Mosaic causes mottled leaves with curled, shriveled tips, while leaf rolling results in upward curling of the leaf margins, sometimes forming cylindrical shapes. In Jiaoxian County, the most prevalent form is the lobular virus.
Controlling viral infections requires improved agricultural practices, including proper spacing, adequate fertilization with phosphorus and potassium, and timely removal of infected plants. Aphid control is critical, as they act as vectors for the virus. Spraying a mixture of 1.5% Plant Disease Ling (1000 times dilution) and 20% Virus A (600 times dilution) every 7 days, up to 3–4 times, has proven effective in preventing virus spread.