symptom
The disease is widespread in the spinach planting area and mainly damages the leaves. Lesions are light green dots at the beginning, with inconspicuous edges, and after expansion, they are irregular in shape, with a diameter of 3 to 17 mm. A gray-white mold layer is produced on the leaf back lesions, and then turns grayish-purple. Lesions spread upwards from the lower part of the plant. During drought, the diseased leaves turn yellow, and when the humidity is high, they often rot. In severe cases, the entire plant leaves turn yellow and die. Some vegetable plants are shriveled, mostly caused by systemic infection before winter.
pathogen
Peronospora farinosa (Fr.: fr.) Fr.f.sp.spinaciae Byford, said spinach downy mildew, belongs to Pseudobacteria Oomycota downy mildew. Cyst peduncles protrude from the stomata, 250-450 μm in size, colorless, branched at an acute angle with the main axis, and branched 3-6 times. Sporangia ovate, without papillae, oospore spherical. The fungus only affects spinach.
Transmission routes and disease conditions
The fungus overwinters as hyphae on damaged hosts and seeds or as oospores in diseased leaves. Conidia are produced in the following spring, and spread by air currents, rain, agricultural tools, insects and agricultural operations. The spores germinate and produce germ tubes that invade the host epidermis or stomata, and then produce sporangia in the diseased part for re-infection. The optimum temperature for conidia formation is 7-15°C; the optimum temperature for germination is 8-10°C, with a maximum of 24°C and a minimum of 3°C. Under low temperature and high humidity conditions with a temperature of 10°C and a relative humidity of 85%, or when the planting density is too large, water accumulation and early sowing are severe.
Prevention method
① In the spinach field in early spring, if the shrunken plants infected by the system are found, they should be pulled out in time, and taken out of the field to be burned. ②Crop rotation for 2 to 3 years should be implemented in severely diseased areas, and cultivation management should be strengthened to achieve appropriate density, scientific irrigation, and reduce field humidity.
③At the initial stage of the onset, spray 60% azole ether·Dysenlian water dispersible granules 1500 times liquid, 500g/L fluazinam suspension concentrate 1800 times liquid or 52.5% xanthone·cymoxanil water dispersible granules 1500 times liquid, 70% Manganese zinc · ethyl aluminum wettable powder 500 times liquid, 250g/L azoxystrobin suspending agent 1500 times liquid, once every 7 to 10 days, continuous control 2 to 3 times.
