What are the control methods for sweet potato stem nematode disease?
Sweet potato stem nematode disease, commonly known as “chaff heart disease”.
[Pathogen nematode scientific name] Ditylenchus destrutor Thorne.
[Host crops] Sweet potato, potato, lily, ginseng, mint, Angelica sinensis, etc.
[Disease diagnosis] It mainly damages the tuberous roots, followed by the stems and vines. When tuberous roots are affected, the flesh appears as strip-like white or brown powdery cavities containing large numbers of nematodes, making the flesh dry and cottony, with weight significantly reduced; when tapped with the hand, a hollow sound is produced. Affected tubers are difficult to identify by appearance at first harvest, and after storage the skin turns liver-colored. Affected seedlings are mainly damaged on the white portion at the base; the affected epidermis shows blue-purple block-like or strip-like halos, and in severe cases the pith becomes brown and dry-rotted. On the stems and vines, yellowish-brown cracks usually appear on the epidermis of the base of the main vine at 7-10 cm above the ground, later gradually turning brown, with the pith becoming white and dry-rotted; in severe cases the affected stems and vines become thickened and break easily. The pathogen nematode is the potato stem nematode; both female and male adults are worm-shaped and slender, slightly tapered at both ends, with a body length of about 1 mm. Larvae are short, small and slender, and eggs are oval.
[Occurrence pattern] The pathogen nematode overwinters in the egg, larval and adult stages with harvested tuberous roots in storage pits, and can also overwinter as larvae and adults in soil and manure. The pathogen nematode is mainly spread by tuberous roots and seedlings, and can also be spread over long distances. In the field it can be spread by soil, manure, rainwater and irrigation water, humans and livestock, and farm tools; raising seedlings in old seedbeds can also spread it. The pathogen nematode is tolerant to low temperatures, becoming active at 2°C, and laying eggs and hatching above 7°C. The optimum temperature for activity is 25-30°C. It prefers to be active in moist, well-aerated sandy soil.
[Control measures] (1) Choose disease-resistant varieties, such as Lu Shu No. 7, Liao Shu 40, Beijing 553, Ji Shu No. 10, etc. (2) Establish disease-free seed-production fields, select disease-free seed tubers or use high-cut seedlings to prevent seedlings from carrying nematodes. (3) Apply thoroughly decomposed manure, and do not use diseased tubers or the dried tuber slices and diseased vines made from them as feed, to prevent the pathogen nematode from entering manure through the livestock digestive tract and spreading. (4) In heavily infested land, carry out crop rotation with grain crops, tobacco, cotton, etc. for more than 3 years; flooded and dry rotation is better. (5) Maintain field sanitation; when diseased plants are found in the field, pull them out with roots and bury them deeply or burn them. After harvesting a diseased field, thoroughly remove diseased residues from the field and deep-plow the soil. (6) For chemical control, 5% stem nematode-killing granules can be used, applied at 1-1.5 kg per 667 sq m scattered at the base of the sweet potato vine stems, then covered with soil and watered.