symptom
After the seedlings are unearthed, the true leaves are more prone to disease, or the seedlings are not unearthed 12 to 16 days after sowing. After the seedbed soil is shallowly opened, only the radicle and rotten dead cotyledons are found. In the early stage of seedling disease, the base of the stem is water-soaked, and later the diseased part turns yellowish-brown, and gradually shrinks into a thin line. The low-lying places in the middle of the seedbed are prone to disease, and there are local patches of dead seedlings. The main cause of the disease is that the seedbed has high humidity and is at a low temperature below 10°C; or the seeding is too dense, the seedlings are not thinned or the seedlings are not thinned in time, and the ventilation is poor.
pathogen
Pythium aphanidermatum (Edson) Fitzp., said Pythium melon fruit, belongs to Pseudobacteria Oomycota Pythium.
Transmission routes and disease conditions
It mainly survives the winter in the soil with chlamydospores along with the diseased residues. The fungus can also live saprophytically in soil organic matter, and generally survive for 2 to 3 years. Chlamydospores germinate to produce hyphae, which invade directly by contact, and are spread by rainwater, irrigation water, agricultural tools and bacteria-carrying fertilizers. The optimum temperature for growth is 20-40°C, the lowest is 14-15°C, and the highest is 40-42°C. Celery is prone to disease due to waterlogging or high humidity, poor permeability, or too deep planting, too wet soil, or application of insufficiently decomposed organic fertilizers; low temperature in seedling stage, long duration of high humidity or frequent rainy days, neutral and slightly acidic Soil, severe disease.
Prevention method
①Choose varieties with better resistance.
② Sowing at the right time. The seedbed is selected in the leeward and sunny place. Before sowing, soak the seeds in warm water at 45-50°C for 10-15 minutes, then soak the seeds in warm water at 20-30°C for 4-6 hours, wash the seed packs with clean water 2-3 times, drain, and dry in the air for 24 hours. Moisturize and accelerate germination at 15-20°C, and sow after 60% of the seeds are white.
③ Soil disinfection. Before sowing, spray 80-120ml of 15% hymexazol water solution into the soil for every 10m2 of furrow, or add 30-40kg of fine soil, mix well and sprinkle it into the furrow, and then mix the soil medicine in the furrow evenly. Protecting seedlings with medicinal soil: mix 8-12ml of 15% hymexazol water per square meter with 5-8kg of sifted fine soil or fine sand, spread 1/3 of the medicinal soil on the surface of the seedbed when sowing, and the remaining 2/ 3 of medicinal soil as seed cover soil. Foliar spray: Spray 70% hymexazol wettable powder 1800 times liquid or 70% Disenlian water dispersible granule 500-600 times liquid or 30% kresoxim-methyl wettable powder 1200-1500 times liquid, 2.5% fludiomycin Nitrile suspension 1000 times liquid.
