What are the latest control measures for potato late blight?
Potato late blight, also known as blight, is a widespread and serious epidemic disease. It occurs in all areas where potatoes are grown. When late blight epidemics occur in susceptible varieties, field yield losses can reach 20%-50%, and storage losses range from 5%-10% in mild cases to more than 30% in severe cases. Late blight not only harms potatoes but can also cause damage to tomatoes, peppers, eggplants and others.
Host crops
Potato, tomato, eggplant.
Disease diagnosis
Leaves, petioles, stems and tubers can all be affected, with symptoms mostly appearing around flowering. When leaves are infected, water-soaked spots begin to appear from the leaf tip or leaf margin. Under high humidity, they quickly expand into brown lesions with water-soaked edges, producing a ring of white mold-like growth, with the mold layer especially obvious on the underside of the leaves. When petioles and stems are affected, dark brown streaks appear, with less white mold, often causing leaves to wilt, dry up and droop, and in the later stage the entire plant becomes a black, wet rot. When tubers are affected, the lesions are brown to purplish-brown, and the tuber flesh beneath the diseased area also turns reddish-brown. The lesions expand into irregular patches, and the boundary between diseased and healthy tissue is often unclear. The diseased area mostly does not extend deep into the interior, often appearing dry, hard and necrotic. In the later stage, it is prone to secondary infection by miscellaneous microorganisms, causing soft rot with an off-odor, making it unfit for consumption. During cellar storage, the diseased area can continue to develop, causing extensive rotting.
The pathogen is Phytophthora infestans. The fungal hyphae are colorless, non-septate, multinucleate and slender. The sporangiophores are colorless, growing singly or in bundles from the stomata, branched, with uneven thickness in the upper part forming nodular swellings. The sporangia are colorless, ovoid, with a papilla at the apex, and produce zoospores after absorbing water. The zoospores are kidney-shaped with two flagella borne laterally. The pathogen can form dormant chlamydospores within the hyphae.
Disease cycle
The pathogen mainly overwinters as mycelium latent in tubers, becoming the primary source of disease infection. After planting diseased tubers, in severe cases they fail to sprout or the sprouts die before emerging from the soil; in mild cases they emerge and then develop disease, becoming center plants. The diseased areas produce sporangia. They spread via air currents and rain for secondary infection, expanding and spreading. Sporangia can also infiltrate the soil with water to infect tubers, forming diseased tubers that serve as the infection source for the following year. The pathogen prefers warm days, cool nights and high humidity conditions. A relative humidity above 95% and temperatures of 18-22°C favor sporangium formation. In rainy years, with frequent morning and evening fog and dew and moist weather, disease occurrence and spread are favored. In northern potato-growing areas, the period around flowering often coincides with the rainy season. If the variety is susceptible, with warm and humid conditions, the disease can spread and become epidemic throughout the field 10-14 days after the appearance of center plants.
Control measures
1. Use resistant varieties
Each region should select resistant, high-yielding improved varieties suitable for local conditions based on local characteristics.
2. Select disease-free seed tubers
Establish disease-free seed production fields, select disease-free seed tubers, and ensure that at every step - autumn harvest and cellaring, winter storage inspection, spring removal from storage, cutting before planting, and the vernalization process - diseased tubers are strictly removed to avoid planting diseased tubers and reduce the primary infection source.
3. Strengthen cultivation management
Plant early at the appropriate time, choose loose-textured, well-drained plots, fertilize rationally, keep plants vigorous and enhance resistance. When center plants are found, pull them out and destroy them promptly.
4. Timely chemical control
Spray immediately upon seeing center plants. You may choose 40% fosetyl-aluminum wettable powder at 300 times dilution, or 70% mancozeb wettable powder at 600 times dilution, or 25% metalaxyl wettable powder at 800 times dilution, or 64% oxadixyl-mancozeb wettable powder at 400 times dilution, or 72.2% propamocarb aqueous solution at 800 times dilution, or 72% cymoxanil-mancozeb wettable powder at 600 times dilution, or 47% kasugamycin-copper oxychloride wettable powder at 800 times dilution, or 69% dimethomorph-mancozeb wettable powder at 1000 times dilution.