Symptom Identification and Control Methods for Major Potato Pests and Diseases

The main potato diseases include: potato ring rot, potato wart disease, potato late blight, potato early blight, potato blackleg, potato bacterial wilt, and others. The main insect pests include: potato tuber moth, 28-spotted ladybird beetle, and underground pests (cutworms, white grubs, wireworms, mole crickets, etc.). Among these, three are nationally quarantined pests: potato tuber moth, potato ring rot, and potato wart disease.

Main Potato Diseases

Potato Ring Rot

Field symptoms generally appear after the flowering stage. Initial symptoms show chlorosis between the veins, appearing mottled, after which the leaf margins or entire leaves turn yellow and withered, and curl upward. The disease starts from the lower leaves of the plant and then gradually develops upward to the whole plant. Due to differences in environmental conditions and varietal resistance, plant symptoms vary greatly. It can cause wilting and necrotic spots on aboveground stems and leaves, and ring-shaped rotting of the vascular bundles in underground tubers. Necrotic spot type: symptoms mostly appear first at the top of compound leaves at the base of the plant. Leaf tips and margins remain green, while the mesophyll turns yellow-green or gray-green with obvious mottling. Leaf tips turn brown and dry up, and leaves curl inward longitudinally. The vascular bundles in the diseased stem turn brown. Wilting type: occurs from the bud stage. Leaves wilt and die from bottom to top, leaf margins curl longitudinally toward the leaf surface, showing dehydration-type wilting. The vascular bundles at the stem base turn pale yellow or yellow-brown, and the plant dies prematurely.

When tubers are mildly infected, there are no obvious external symptoms. As the disease progresses, the skin color darkens, the eyes turn black and die, and the surface may crack. When cut open, the vascular bundles can be seen as a milky white or yellow-brown ring-shaped area. In mild cases, squeezing by hand exudes milky yellow bacterial slime. In severely diseased tubers, the diseased area turns dark brown, forming ring-shaped cavities. When squeezed by hand, the skin separates easily from the flesh, often accompanied by invasion of saprophytic bacteria.

Control methods:

Integrated measures should be adopted, combining the use of resistant varieties, removal of diseased plants in the field, and application of low-toxicity pesticides. During the seedling stage and adult plant stage, dig out and remove diseased plants and dispose of them centrally. When disease occurs in the field, spray 72% agricultural streptomycin at 4000x dilution, or 2% kasugamycin wettable powder at 500x dilution, or 77% Kocide wettable micro-powder at 500x dilution, or 25% copper ammonia complex aqueous solution at 300x dilution, or 50% DT wettable powder at 500x dilution.

Potato Wart Disease

After the underground stem base, tubers, and stolons of potato are infected, large, malformed, rough, spongy tumors form, sometimes surrounding the entire stem base, closely resembling cauliflower. Young tubers become entirely malformed, while larger tubers mostly form malformed warty tumors at the eyes. Highly susceptible varieties form small warty tumors on axillary buds and between stems. The number and size of warty tumors vary depending on the susceptibility of the variety, how early infection occurs, the number of infection points, and the severity of the disease. Warty tumors are initially white and glossy, gradually turning green upon exposure to light, and finally turning brown to black and rotting. On highly susceptible varieties, stems, pedicels, calyxes, and leaf undersides may produce clustered small leaflets that are sessile, with a main vein but no branching veins.

Control methods:

(1) Strict quarantine, delineate epidemic areas and protected areas. It is strictly prohibited to transport seed potatoes out of epidemic areas, and soil from diseased fields and plants growing on it are also strictly prohibited from being moved out;

(2) Select resistant varieties. Resistance varies greatly among varieties. The potato variety "Mili" in our province shows high resistance and can be selected according to local conditions.

(3) Severely diseased land should not be planted with potatoes. Generally diseased land should, based on actual conditions, be rotated to non-solanaceous crops;

(4) Strengthen cultivation management. Carry out frequent cultivation and apply clean manure, increase phosphorus and potassium fertilizer, and promptly dig out diseased plants and burn them centrally;

(5) When necessary, carry out soil disinfection in diseased fields;

(6) Apply pesticides early for control. For fields with gentle slopes and inconvenient water sources, during the period from 70% plant emergence to full emergence, irrigate with 20% triadimefon emulsifiable concentrate at 1500x dilution; for fields with inconvenient water sources, spray 20% triadimefon emulsifiable concentrate at 2000x dilution during the seedling and bud stages, spraying 50-60 liters of prepared solution per mu each time, which has a certain control effect.

Potato Early Blight

When seedlings are infected, they develop damping-off, causing seedling death. During the adult plant stage, leaf infection is widespread and severe. Leaf infection mostly starts from the lower leaves and develops upward to the upper leaves. Initially, small chlorotic spots form on the leaves, which gradually expand to form round or irregular lesions of varying sizes. The lesions are brown to dark brown, mostly with a light green or yellow halo at the margins, and the center of the lesion has obvious concentric raised rings. In severe cases, multiple lesions can merge into large irregular patches, causing premature leaf death. Petiole lesions are elliptical, dark brown to black, with concentric rings. When lesions are large, they cause leaves to droop and die. Stems are also susceptible. Stem infection mostly occurs at branching points. Lesions are elliptical, elongated spindle-shaped, or irregular, brown to dark brown, slightly sunken, with inconspicuous concentric rings, and a gray-black moldy growth on the surface. Stems and branches tend to break at the lesion sites. Fruit infection mostly occurs near the fruit stalk, producing nearly circular or elliptical, sunken lesions 10-30 mm in diameter. The lesions are brown to dark brown, with obvious concentric rings, covered with black mold. The lesion area is relatively hard, generally does not rot, and sometimes cracks open from the lesion site in later stages. Potato early blight can sometimes also damage tubers, forming round or irregular, dark, slightly sunken lesions with clear margins. The diseased area can extend half a centimeter below the skin, the tuber flesh turns brown, and later develops dry rot.

Control methods: