How to control tobacco anthracnose? What preventive measures are there?

Tobacco anthracnose is a common disease in the growth process, which mostly occurs at seedling stage, mainly harming leaves and greatly affecting the planting benefits of tobacco farmers. So, how can tobacco farmers control tobacco anthracnose? This paper will make a detailed summary for everyone for farmers' reference.

Symptoms:

At the seedling stage, the diseased spots on the leaves were dark green waterlogged spots at first, and after 1-2 days, they expanded into reticular spots with a diameter of 2-5 mm, slightly depressed, and the edges were obviously slightly convex, showing reddish brown. When the weather is wet, the lesions are mostly brown or yellowish brown, and sometimes there are wheel marks or small black spots. When the weather is dry and the host tissue is hard, there are no wheel marks or small black spots on the lesion. When the lesions are dense, they merge with each other, causing the leaves to shrink and burn. The lesions on midvein, lateral vein, petiole and stem are spindle-shaped, sunken and cracked. Large or more diseased spots often cause seedlings to turn back. The disease started from the foot leaves in the adult stage and gradually spread upward, and the symptoms of the lesion were basically the same as those in the seedling stage. The diseased spot on the stem is large, dark brown, cracked and sunken, showing longitudinal fissure network stripes, and small black spots appear on the diseased part when the weather is wet. If flowers and fruits are killed, they will produce brown and nearly round spots.

Occurrence law:

The main source of infection of seedbed diseases in the second year is that hyphae and conidia stay on the soil and manure with diseased residues for the winter, or hyphae and conidia in seeds attach to the surface of seeds for the winter. Germs are spread by wind and rain, conidia are only produced under wet conditions, and can germinate and infect when there is water film. It is rainy at seedling stage, and diseases are often serious. Low humidity of seedbed or flooding will cause diseases. The pathogen of field diseases mainly comes from diseased seedlings, followed by the residue of diseased plants in soil and fertilizer. Field diseases-usually confined to the bottom leaves, can spread to the top leaves and inflorescences when it rains. The optimum temperature of anthrax is 25-30℃, and the incidence below 4℃ and above 35℃ is rare. Water plays a decisive role in the propagation and spread of this strain, and it is easy to form and spread conidia for reinfection under wet and rainy conditions. It is rainy and humid, the tobacco seedlings in the seedbed are too dense, the drainage is not smooth, the ventilation after film mulching is poor, and the disease is aggravated by poor management. Tobacco seedlings are most susceptible to infection before and after two real leaves, which often makes the whole border tobacco seedlings sick and even die a few days later.

Prevention and control methods:

The prevention and treatment of the disease should focus on the seedling stage. The key link is to set seedlings reasonably, reduce shading, control the temperature and humidity of seedbed, reduce the chance of infection by germs, and take protective measures such as applying net fertilizer and spraying chemicals to achieve the purpose of cultivating strong seedlings. Choose a plot far away from vegetable fields, tobacco fields and curing barn, with high terrain and convenient drainage, and the previous crop is paddy field or the plot without solanaceae or cucurbitaceae crops as the seedbed. Popularizing film seedling raising without applying bacterial fertilizer can reduce the occurrence of diseases. Strengthen seedling management. The seedbed should avoid water accumulation and the bed surface is too wet, pay attention to controlling the sowing density, so as to achieve early planting spacing and early seedling setting and cultivate strong seedlings. If the seedlings are covered with plastic film, when the temperature is high, the plastic film on the border will open early and close late, which is convenient for ventilation.

Seed treatment is an effective measure to prevent anthracnose. Soak the seeds in 1% copper sulfate, 0. 1% silver nitrate or 2% formalin solution for 10 minute, then wash them with clear water, dry them to accelerate germination and sow them.

Before planting, use the method of burning soil or using criminals. The seedbed can be fumigated with 7% weibaimu aqueous solution, or treated with a mixture of 40% pentachloronitrobenzene and 80% zineb (1: 1), and the dosage per square meter is 10g. Spraying1:150 times bordeaux solution every 7- 10 days for 3 consecutive times from the tobacco seedling hybridization period.

Before transplanting tobacco seedlings, the following chemicals can be sprayed: 70% mancozeb wettable powder 500 times solution; 500 times solution of 75% chlorothalonil wettable powder; 80% zineb wettable powder 80-100g/mu, water 60-70kg; Control effect of 500 times solution of 50% carbendazim wettable powder. At the beginning of the disease after transplantation, the following drugs can be used: 25% prochloraz manganese salt EC 1000 times solution; 60% difenoconazole thiram wettable powder100-150g/mu, and 50-60kg of water; 20% thiophanate carbendazim suspension 100- 125ml/ mu, 50-60kg water; 50% junhejing wettable powder 1000 times solution; 50% thiophanate-methyl wettable powder 1000 times solution; 600-800 times of 50% Kelantan wettable powder; 600 times solution of 80% thiram zinc wettable powder; 24% benzoxazole suspension concentrate 900- 1200 times; 40% flusilazole emulsifiable concentrate 4000-6000 times; 5% and 600-700 times of amizole wettable powder, every 7 7- 10/day 1 time, 2-3 times in a row, and 4-5 times in severe cases.