I. Symptoms: Tomato early blight mainly affects leaves, stems, flowers, and fruits. The leaves were initially presented with small black spots with large needlepoints. They developed into continuously expanding round striated spots. There were more light green or yellow halos on the edges, and the central circle was concentric; the stems were infected, and brown irregular circles were often generated at the branches. In the form of elliptical lesions, the surface is gray-black moldy, infected with green fruits, beginning near the calyx, beginning with an oval or indefinite brown or black spots and depressions, later fruit cracking, diseased part of the hard, dense black mold layer.
Second, the route of transmission and the occurrence of conditions, laws: the mycelium or conidia in the sickle or seed overwintering, directly from the stomata, lenticels or epidermis invade, the formation of primary spores, and through the air flow, rain repeated several times Infection. When the tomato enters vigorous growth and the fruit rapidly expands, the basal leaves start to age. If the average temperature is 21 degrees Celsius for 5 days and the relative temperature is greater than 70% for more than 49 hours, the disease begins to become prevalent. The occurrence of early blight is based on several years of observations. The incidence of early sowing is mainly due to relatively late sowing. The middle group in the same shed has a heavier incidence in the middle group than in the side group. The deficiency of basal fertilizer and the deficiency of phosphorus and potassium fertilizers are relatively serious.
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