Recommendations for the Occurrence and Control of Pests and Diseases in Winter Potatoes

In recent years, the potato planting area in our city has been continuously expanding, and various potato pests and diseases have been occurring in succession, seriously affecting potato yield and quality. It is currently the potato growing season. According to recent surveys conducted by our station and the Huidong station in Tieyong, Renshan and other places, the main pests and diseases occurring in winter potatoes in our city include: potato bacterial wilt, blackleg, late blight, viral diseases, as well as underground pests and aphids. All localities should strengthen surveys, and in particular, do a good job in controlling soil-borne diseases of potatoes.

I. Occurrence of Pests and Diseases

1. Bacterial wilt: The typical symptom in the field is acute wilting of leaves, branches or the whole plant, that is, wilting while still green, with the vascular bundles at the base of the stem turning yellow or yellowish-brown. When the tuber is cut crosswise, the cut surface shows ring-shaped decay, and turbid white bacterial ooze automatically exudes from the vascular bundles. In some early-planted fields, the diseased plant rate is generally 2.6-5.2%, with the highest reaching 13.3% in a few severe cases.

2. Blackleg: It mainly infects stems or tubers, and can occur from the seedling stage to the late growth stage. Infected seedlings are generally stunted, with shortened internodes, or leaves rolling upward, chlorosis and yellowing, or the base turning black, and then wilting and dying. A cross-section of the stem shows three main vascular bundles turning brown. In some early-planted fields, the diseased plant rate is generally 1.7-3.5%, with the highest reaching 6.1% in a few severe cases.

3. Late blight: It is a devastating epidemic disease. On leaves, symptoms usually start from the leaf tip or leaf margin, initially as water-soaked chlorotic spots, which then gradually expand into nearly circular, dark brown lesions with a ring of white mold on the edge. At the same time, the lesions can spread along the leaf veins to the petiole and stem, forming brown streaks. In severe cases, the leaves wilt and turn black, which can cause the death of the whole plant. In some early-planted fields, the diseased plant rate is generally 1.23-3.78%, with the highest reaching 6.37%.

4. Viral diseases: Depending on the pathogenic virus, field symptoms vary greatly, generally appearing as mosaic, yellow spots, leaf curling, wrinkling, witches' broom, yellow dwarf, purple top wilting, etc. They are mainly transmitted through sap friction and by insects such as aphids. In affected fields, the diseased plant rate is generally 0.5-1.7%, with the highest reaching 3.6% in a few cases.

5. Underground pests: Mainly cutworms, mole crickets, etc., which can bite off the underground stems of seedlings, causing the seedlings to wither and die, and can also feed on tubers, causing disease infection and affecting tuber quality. In affected fields, the damage rate to small seedlings is generally 0.64-2.25%, with the highest reaching 5.79%.

In addition, potato ring rot, aphids, 28-spotted ladybird beetles, etc. also occur to varying degrees.

II. Control Recommendations

During the potato growing period, the plant protection policy of "prevention first, combining prevention and control" should be adopted, fertilizer and water management should be strengthened, field humidity should be controlled, and diseased plants should be promptly removed from fields with initial disease occurrence to reduce the spread and proliferation of pathogens, creating an environment favorable for plant growth and unfavorable for the occurrence of pests and diseases.

1. Bacterial wilt, blackleg, ring rot: In fields with initial disease occurrence, diseased plants should be promptly removed, lime should be spread in the holes, and field water should be drained to avoid flood irrigation and continuous irrigation, thereby reducing the spread and proliferation of pathogens. For other plants, 20% Yekuning (Yeqingshuang, Chuanhua 018) 100 g mixed with 60-80 kg of water per mu, or 25.9% Zhibaoling aqueous solution 100 mL, or 50% Xiaojunling soluble powder 1000-1500 times solution can be used for drenching or spraying 2-3 times for protective application. For severe cases, the dosage and water volume can be increased to control the expansion and spread of the disease.

2. Late blight: Control should focus on the middle and late stages, and pesticide should be applied immediately after finding the central diseased plant. Chemicals that can be used include 58% Ridomil-MZ wettable powder 75-120 g plus 40-60 kg of water, 25% metalaxyl 150-200 g plus 60 kg of water, 72% Kelu wettable powder 500 times solution, Sandofan 500 times solution, and 75% chlorothalonil 600-800 times solution, etc. Choose one for rotation use each time.

3. Viral diseases, aphids: If wrinkled mosaic, leaf curling, leaf wilting, and ring rot plants appear 15-20 days after emergence, they should be promptly removed. In the early stage of disease occurrence, spray the leaf surface with Virus A 500-700 times solution 2-3 times. After full emergence and around flowering, do a good job in aphid control. Use 2.5% pymetrozine wettable powder 20 g or 10% imidacloprid 15 g per mu, add 50 kg of water, and spray 2-3 times.

4. Underground pests: Mainly control cutworms, mole crickets, etc. First, mix Lesiben granules or Dichong Susha granules with base fertilizer and apply them in the fertilization furrow (or apply them when hilling), to poison and kill underground pests damaging the seedling stage; second, in combination with the first and last fertilizer drenching, use 90% crystal trichlorfon 800-1000 times solution, or 50% phoxim or deltamethrin 1000 times solution, or 50% fenitrothion 1000-2000 times solution, etc. for spraying to protect seedlings.