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Strictly prevent the spread of sweet potato black spot disease
It is crucial to prevent the spread of diseased potatoes and apply pesticides effectively. According to the **China Pesticide Network**, here are some key measures to manage this issue:
The disease can occur during both the growth and storage periods, primarily affecting potato seedlings and tubers, but not the green parts of the plant. In seedlings, a black, round, slightly sunken spot appears on the white part of the stem, which later leads to stem rot and plant death. A mildew layer forms on the affected area. For tubers, the disease initially appears as small black spots that gradually expand into irregular black-green patches. A grayish layer develops on the surface, followed by the formation of black spines. Infected potatoes have a bitter taste and can continue to spread the disease during storage, leading to rot.
The sexual stage of the pathogen produces ascospores. These are found in the center of lesions, with a spherical base and a long, striped neck. Each ascus contains eight colorless, helmet-shaped ascospores, measuring 4.5–7.8 × 3.5–4.7 μm. Although they have a short lifespan, they play a significant role in disease transmission during storage. The hyphae start as colorless and transparent, then turn dark brown when mature, with a width of 3–5 μm. They grow inside host cells or between them. The asexual stage produces conidia and chlamydospores. Conidiophores are cylindrical or dumbbell-shaped, ranging from 9.3–50.6 × 2.8–5.6 μm. After germination, conidia may form chains, leading to the development of sclerotia after 2–3 generations. Some also produce thick-walled, dark brown chlamydospores, measuring 10.3–18.9 × 6.7–10.3 μm.
The pathogen overwinters in the soil, in storage areas, or on seed potatoes, either as mycelium or spores. It becomes the primary source of infection in the following years. The pathogen can infect seedling roots directly or through wounds, lenticels, and root surfaces. It often spreads quickly once symptoms appear.
The disease thrives in low-lying areas, heavy soils, and during rainy seasons. High humidity and poor ventilation further increase disease severity.
To control the disease, consider the following methods:
(1) Establish disease-free seed fields and carefully select healthy seed potatoes to avoid spreading infected material.
(2) Soak seed potatoes in a 50% carbendazim WP solution diluted at 1000 times for 5 minutes.
(3) Choose resistant varieties such as Jinshu No. 6, Hushu No. 2, Xiangshu No. 15, Legacy 190 Sweet Potato, Lushu No. 2, Lushu No. 3, Lushu No. 7, Beijing 553, Jishu No. 10, and others.
(4) After cutting the seedlings, soak them in a 50% thiophanate-methyl WP solution diluted at 1500 times for 10 minutes, ensuring the solution covers about one-third to half of the vines.
By implementing these practices, farmers can significantly reduce the risk of disease and improve crop health.