Scars is a serious potato disease that often occurs alongside late blight. When the disease strikes, brown spots first appear on the surface of the tubers and gradually expand into larger, irregular brown patches. The formation of numerous corky cells leads to a rough texture on the skin. Over time, the center may either sink or bulge, forming a scab-like hard plaque. Importantly, the lesion remains on the outer layer of the potato and does not penetrate deep into the tuber, distinguishing it from whitefly disease.
Disease Conditions: The infection usually occurs before the tuber develops, with bacteria entering through lenticels or wounds. The disease thrives in temperatures between 25°C and 30°C, especially in neutral or slightly alkaline sandy loam soils. Soils with a pH below 5.2 have lower incidence rates. Different potato varieties show varying levels of resistance. Thin-skinned varieties are more susceptible, while thick and brown-skinned ones tend to be more resistant.
Control Methods: Choose disease-resistant varieties, apply well-decomposed organic manure or green manure to reduce infection rates, and ensure proper irrigation to avoid drought stress.
2. Whitefly Disease
Whitefly disease primarily affects the tubers and roots, though stems can also become infected. Early symptoms include small brown spots on the epidermis, surrounded by a translucent yellow halo. These spots gradually grow and form raised lesions about 3-5 mm in diameter, resembling freckles. At this stage, the epidermis is still intact, known as the "closed cricket" stage. As the disease progresses, the epidermis cracks, exposing an orange-red subcutaneous layer and releasing dark brown spores. The lesion then becomes crater-like, with a hardened, coriaceous ring around it—this is the "open cricket" stage. Infected roots may develop bean-shaped swellings on their sides.
Disease Conditions: The disease thrives in soils with over 90% moisture, at temperatures between 18°C and 20°C, and a pH range of 4.7 to 5.4. The severity depends mainly on initial infections, and secondary spread in the field has less impact.
Prevention and Control: Use disease-free seed potatoes and treat them by soaking in 40% formalin diluted 200 times for 5 minutes, followed by covering with plastic for 2 hours before drying and planting. Increase the use of decomposed organic matter or bio-fertilizers, add wood ash to adjust soil pH, and avoid flood irrigation. Planting sorghum can also help prevent the spread of pathogens.
3. Virus Disease
(I) Cause: Potato virus disease is a major threat, often caused by the use of contaminated seed potatoes, extensive cultivation without proper management, lack of fertilization, and insufficient water supply, which worsen the condition.
(B) Symptoms: Infected plants become stunted and deformed, with reduced yield. The virus can degrade seedlings. Once infected, the main symptoms include wrinkled mosaic and leaf rolling. 1. Mosaic disease causes dark and light green mottling on leaves, which shrink and curl downward, leading to a dwarfed appearance. 2. Leaf rolling results in upward curling of the leaf margins, sometimes forming a cylindrical shape. The affected leaves are smaller and lighter in color, with occasional red or purple discoloration on the underside. In Jiaoxian County, the most common type is the lobular virus.
(III) Control Methods: Improve cultivation practices by increasing row spacing, applying sufficient base fertilizer, and using more phosphorus and potassium. Ensure proper irrigation and promptly remove diseased plants to reduce disease spread. Implement aphid control measures early after emergence to prevent virus transmission. For chemical control, spray a mixture of 1.5% plant disease ling diluted 1000 times and 20% virus A diluted 600 times every 7 days, repeating 3–4 times for effective prevention.