1. Pathogens and pathogenesis.
Green onion purple spot disease is a fungal disease, the fungus overwinters by mycelium or conidia on the diseased residue or seedlings, and is spread by air flow and rainwater, and the pathogen invades through the stomata on the surface of the onion, wound or directly through the epidermis. The disease is easy to occur under warm and humid conditions, the suitable temperature for the onset is 25 27, less than 12 does not occur, warm and humid disease is serious. Autumn temperatures are just right for germs to multiply. Sandy soil, dry land, early seedlings or old seedlings, lack of fertilizer, and green thrips are the most harmful fields, and the disease is serious.
2. Disease symptoms.
Symptoms: oval or fusiform, brown to purple, etc.
Alternaria Porri (Ell) Ciferri is a subphylum of Hemiphyllum and is called Alternaria chivesis. It mainly damages leaves and peduncles, and occasionally bulbs. The disease mainly affects leaves and peduncles, mostly from the tips of leaves and middle peduncles, and can also harm bulbs. At the beginning of the disease, the lesions are small and slightly depressed, and then gradually become larger, oval or fusiform, brown to purple. When wet, the lesion has a black mold layer and concentric wheel lines, and the diseased part is easy to break. After the peduncle is damaged, it often causes the seeds to shrink and cannot fully mature and affect the seed collection. The lesions on green onions and onions are purple-brown, and the garlic spots are yellowish-brown. Pathogenic characteristics: The pathogen overwinters in the soil with mycelium in the host, on the seedlings or with the diseased residue, and can also continue to damage the stored green onions.
3. Mode of transmission.
1. Green onion purple spot disease is mostly harmed by conidia on onion crops in southern China. In the cold regions of the north, mycelium overwinters in the host or on diseased remains.
2. Green onion purple spot disease can be spread by air flow or rainwater, and invade from stomata, wound or epidermis, with an incubation period of 1 4 days. Suction wounds are an important route for pathogen invasion, so thrips can aggravate the disease when it occurs severely.
3. The appropriate temperature for conidia germination is 24 27, and the appropriate temperature for pathogen development is 6 34.
Four: prevention and control agents.
1. Etherstrobin. Fluconazole.
Difenoconazole + 75% chlorothalonil.
3. Tebuconazole, prochloraz, chlorothalonil, Pythium, iprodione, Dysenlian, propiconazole.
5. Atlas. 