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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 promptly. According to the **China Pesticide Network**, here are some key preventive measures to manage this disease effectively.
This disease can occur during both the growing season and the storage period, primarily affecting potato seedlings and tubers, but it does not harm 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 infected area. For the tubers, the disease initially shows as small black spots, which then expand into irregular black-green patches. A grayish mass develops on the surface, and later, black spines appear. Infected potatoes have a bitter taste and can continue to spread the disease during storage, eventually leading to rotting.
The ascidian crust produced by the sexual stage of the pathogen appears in the center of the lesion. The ascospore shell has a spherical base with a long, neck-like structure on top, and an endogenous pear-shaped ascus containing 8 ascospores. These ascospores are colorless, thin, and helmet-shaped, measuring between 4.5–7.8 μm in length and 3.5–4.7 μm in width. Although their lifespan is short, they play a significant role in disease transmission during storage. The hyphae start off colorless and transparent, turning dark brown when mature, with a width of 3–5 μm. They grow inside the host cells or in the intercellular spaces.
In the asexual stage, the fungus produces conidia and chlamydospores. Conidia form at the tips or sides of hyphae, carried on spore stalks. Conidiophores are colorless, cylindrical, or dumbbell-shaped, ranging from 9.3–50.6 μm in length and 2.8–5.6 μm in width. After spore formation, germination occurs quickly, sometimes forming chains of conidia that lead to the development of sclerotia after 2–3 generations. Some conidia also develop into chlamydospores, which are dark brown, elliptical, and thick-walled, measuring 10.3–18.9 μm in length and 6.7–10.3 μm in width.
The pathogen overwinters in the soil, on storage platforms, or in seedbeds, often in the form of thick spores or ascospores. It can also attach to seed potatoes via mycelium or survive within the tuber itself. This becomes the primary infection source in the following years. The pathogen can directly infect the roots of seedlings or enter through wounds, lenticels, or roots on potato chips, frequently causing infections once the disease takes hold.
The disease tends to be more severe in low-lying areas, heavy clay soils, or during rainy seasons. High humidity and poor ventilation also contribute to increased disease incidence.
To control the disease, consider the following methods:
1. Establish disease-free seed fields and carefully select healthy seed potatoes to prevent the spread of infected material.
2. Soak seed potatoes in a 50% carbendazim WP solution diluted 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 potato seedlings, soak them in a 50% thiophanate-methyl WP solution diluted 1500 times for 10 minutes, ensuring that the solution covers about one-third to half of the vines.
By implementing these practices, you can significantly reduce the risk of disease and protect your potato crops effectively.