How to treat diseases in tobacco seedlings? A detailed guide to prevention and control methods

China is a major tobacco-producing and marketing country in the world, with widespread cultivation across the northern and southern provinces and regions. During cultivation, growing strong seedlings is a key part of the work, and if management is improper, diseases may occur. So, how do you treat diseases in tobacco seedlings?

This depends on what disease has appeared in the tobacco seedlings; different diseases have different prevention and control methods. Diseases that tobacco seedlings are prone to include damping-off, bacterial wilt, black shank, anthracnose and common mosaic virus, among others, and you can choose the corresponding pesticide for prevention and control.

1. Damping-off

(1) Symptoms: It mainly harms tobacco seedlings; diseased seedlings show brown, water-soaked rot near the soil surface. The diseased seedlings look as if they have been scalded with boiling water, and patches of diseased seedlings turn dark green, wilt, lodge and rot. Under humid conditions the pathogen spreads outward in all directions, causing tobacco seedlings to develop the disease in patches.

(2) Prevention and control: When scattered patches of disease are found in the seedbed, you can choose 25% metalaxyl wettable powder at 500-600 times dilution; or 64% oxadixyl-mancozeb wettable powder at 500 times dilution; or 75% chlorothalonil wettable powder at 1000 times dilution; or 40% fosetyl-aluminium wettable powder at 250-300 times dilution for spraying.

2. Bacterial wilt

(1) Symptoms: Tobacco bacterial wilt is a vascular disease, with the typical symptom being wilting. Diseased plants usually wilt on one side, and after pulling them up, the lateral roots on the affected side can be seen to have turned black and rotted, while most of the root system on the side without symptoms remains normal.

(2) Prevention and control methods: Use 200 units of agricultural streptomycin at 50 ml per plant as a root drench, once every 10-15 days, applied 2-3 times in a row, which has a certain preventive and control effect; drench the roots with 600 times dilution of Qingkuling while also spraying the stems and the soil in the root zone.

3. Black shank

(1) Symptoms: When seedlings are infected, dirty black lesions appear at the base of the stem, or the disease starts from the lower leaves and spreads along the petiole to the young stem, causing the seedlings to damp off. When humidity is high, the diseased area becomes covered with white mycelium, and seedlings die in patches.

(2) Prevention and control methods: Before transplanting, spray the seedbed evenly with 58% metalaxyl-mancozeb wettable powder at 500 times dilution. Within 1 month after transplanting, when scattered disease occurs, spray the leaves with Gaoke 30% metalaxyl-hymexazol at 600 times dilution, or remove the nozzle and spray the stem base. Alternatively, at transplanting, mix 100-200 g of 95% dexon per mu with 5 kg of fine soil, spread the medicated soil around the base of the tobacco plant stems, and seal it firmly with soil. After transplanting or before hilling, spray 58% metalaxyl-mancozeb or 95% dexon wettable powder at 500 times dilution.

4. Anthracnose

(1) Symptoms: It can occur at all growth stages of tobacco, but it is common and severe at the seedling stage. Diseased spots densely cover the seedling leaves, and in severe cases the entire batch of tobacco seedlings is often destroyed. In ordinary cases, although the seedlings are not destroyed, the seedlings grow poorly, and after transplanting to the field the disease can continue to cause damage, resulting in relatively large losses.

(2) Prevention and control methods: Before the disease occurs, Bordeaux mixture can be used for prevention. After the disease occurs, you can spray 50% captan wettable powder at 500 times dilution or polyoxin 480. If control can reach more than 90%, you can also use 50% thiram wettable powder at 800 times dilution, or 75% chlorothalonil wettable powder at 500-800 times dilution, or 50% zineb, 80% anthracnose-forma or 50% thiram wettable powder, all sprayed at 500 times dilution.

5. Common mosaic virus

(1) Symptoms: It can occur from the seedbed stage to the mature plant stage in the field. From 20 days after transplanting to the budding stage is the peak period of disease occurrence. After topping, the number of diseased plants in the field still tends to rise, but symptoms mainly appear on tobacco suckers and cause little damage. After seedlings are infected, the vein tissue of new leaves turns light green, showing a semi-transparent “vein-clearing symptom”; when held up to the light, the large and small veins of the diseased leaves are very clearly visible. A few days later, the leaves form a yellow-green “mosaic symptom”.

(2) Prevention and control methods: Spray the leaves with ningnanmycin at (20,000 units)/(ml); alternatively, 0.1% sodium alginate or 0.1% zinc sulfate and 0.3% urea can be sprayed alternately 2-3 times at 3-4 day intervals.