Carrot leaf blotch, also known as leaf spot disease.
[pathogen name] Septoria carotae Nagorn.
[host crop] carrots.
[Disease diagnosis] mainly damages the leaves, but it can also damage the petioles. The incidence of leaves is mostly caused by lesions on the leaf margins. The lesions are nearly round and oval, brown to dark brown, with no obvious edges, and many small black spots are scattered on the lesions later. Petioles onset, lesions spindle-shaped, oblong, dark brown, scattered on many small black spots. When the onset is severe, the leaves are covered with lesions or lesions, causing the leaves to fade early (Figure 8).
The pathogenic bacteria are carrot spores. Conidia nearly spherical, dark brown. Conidia needles, slightly curved, colorless, with 3 to 4 diaphragms.
〔Incidence of the disease 〕 bacteria with the residue scattered on the surface of the ground and the soil in winter, the seeds can also be bacteria, are the primary source of infection. The pathogenic conidia of the pathogenic fungus spewed out of the conidia after being absorbed by water and spread through wind and rain and irrigation water, and penetrated through the stomata or penetrating the epidermis. The disease re-infested frequently and the disease developed rapidly.
The bacteria is warm and wet. The optimum temperature for onset is 25°C, and the relative humidity is required to be above 85%. Water droplets need to be present for contagios spread. Excessive management, heavy growth and weak disease.
〔Prevention〕
(1) Use seeds harvested from disease-free plants. General seeds should be disinfected and can be seeded with 40% seed weight double or 50% thiram with seed weight 0.3%.
(2) Apply manure, timely topdressing, and increase phosphorus and potassium fertilizers. Appropriate irrigation, after the irrigation, strengthen the cultivator loose soil, control the humidity in the field. Immediately rule out the water in the fields after the rain.
(3) Early detection and removal of central diseased strains. Harvest the sick plants in the field and turn the soil deep.
(4) Chemical control in the early stage of onset can be sprayed with 70% mancozeb WP 500 times, or 80% vacant 600 times, or 40% WP WP 500 times , or 40% of the polysulfide suspension 500 times, or 77% can kill 800 times the wettable particulate powder, or 1:160 ~ 200 Bordeaux mixture.
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