Symptoms are also called erythema, hate tiger's eye, fire bubble spot, spot disease. Can invade leaves, stems, pedicels and pods. Leaf disease mostly occurs from the lower leaves and gradually develops upward. At the beginning of the lesion, it was a small yellow-brown spot, followed by a brownish or nearly round spot with a concentric ring of reddish brown or dark brown. When the expansion is faster, yellow halos appear at the edges. Dark brown or black moldy layer can be seen on the spot when the humidity is high. The lesions are brittle and easily broken. In severe cases, lesion fusion causes the leaves to become broken leaves. Veins, pedicels, capsules, and stems are now oblong or spindle dark brown depressions.
The pathogen Altereraria alternata (Fries) Keissler called Alternaria spp. Mycelium septate, colorless. Conidial stems top, with 1-3, brown. The conidia are brown, and the chains are born on the stalks. The bases are large and the tops are smaller. They are in the form of inverted sticks or ellipses. There are many pods, with 1-3 mediastinums and 3-7 septums. The bacteria grow fast and produce toxins. It has been reported that A. longipes, A. tenuis, and A. tabaima can also cause disease.
Transmission routes and pathogenic conditions The mycelium overwinters on the body of the disease. The conidia are produced in the following year, and the initial infection is carried out by airflow propagation. Seeds and transplanted seedlings can also become the primary source of infection in the field. Most of the bacteria invaded from the host's stomata and wounds, and the disease minister re-infected the conidia. The tobacco plants had obvious disease resistance stages, and the seedling stage was more resistant to disease, and the leaves were more sensitive to aging at the physiological maturity stage. The temperature of pathogenic bacteria is 25-30 °C. If there is dew in 12 hours, the bacteria can complete the intrusion at 12-20°C. The temperature is suitable for 48 hours of incubation and the symptoms of hypothermia are prolonged. Rainy days and high humidity are important factors in the epidemic of diseases. The rainy season during harvesting often leads to a pandemic of the disease. Late transplanting, late maturity, late fertilizer application, excessive nitrogen application, and heavy onset after the storm. High planting density, shading in the fields, and heavy harvesting are not timely.
Control methods (1) Selection of resistant (resistant) varieties such as G80, G28, Kirk 176, Kirk 86, Nc95, net yellow, Zhongyan 90, Yiyan 1, Liaoyan l0, Zhongwei l, Chunlei No. 3, iron smoke, etc. (2) Strengthen the cultivation and management of the use of thin film early nursery, early transplanting, so that the disease stage to avoid the rainy season. Timely harvesting and baking. Reasonable and sparse, increase line spacing, improve ventilation and light transmission conditions, and reduce field humidity. Remove weeds in time. Rational fertilization, promote early-onset. Scientific topping, proper amount of leaves, timely removal of the old leaves of the foot. Implement rotation. (3) In the early stage of the disease prevention and control, spraying 50% Mosquito or 50% carbendazim, 70% thiophanate-methyl wettable powder 600-800 times, 70% mancozeb WP 500 times, 1. 5% polyoxin
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