Which pesticides give good control of tobacco anthracnose?
Tobacco anthracnose is caused by infection by fungi of the genus Colletotrichum in the subphylum Deuteromycotina. This disease can occur at all growth stages of tobacco, but it occurs commonly and severely during the seedling stage. The seedling leaves are densely covered with lesions, and when the disease is severe, the entire batch of tobacco seedlings is often destroyed. So what pesticides should be used for tobacco anthracnose?
1. What pesticides should be used for tobacco anthracnose?
The pesticides commonly used for tobacco anthracnose are: copper sulfate, silver nitrate, formalin, chlorothalonil, mancozeb, anthracnose fumei, penconazole, tanteling, thiophanate, and tuijunte.
2. Disease symptoms
Leaf infection: initially dark green water-soaked small spots, which later expand into brown round spots; the center of the lesion is slightly sunken, white to yellowish brown, with a distinct, slightly raised, brown edge. When humid, concentric rings and small black dots form on the lesions. When dry, the diseased tissue becomes old and hard, and the lesions are mostly yellow or white, without concentric rings or black dots. When the disease is severe, the lesions merge into large spots, causing the tobacco leaves to twist and shrink or to scorch and wither.
Infection of leaf veins, petioles and young stems: the lesions are spindle-shaped, brown, sunken and longitudinally cracked; in severe cases the seedlings collapse and break at the petioles. At the mature plant stage, the disease mostly starts on the lower leaves and gradually spreads upward.
Stem infection: the lesions are relatively large, forming longitudinally cracked net-like streaks, sunken, dark brown; when the weather is humid, small black dots grow on the diseased parts. Infection of sepals and capsules produces small brown nearly round spots.
3. Control methods
1. Choose a good seedbed, use film-covered seedling raising, and select and plant disease-resistant varieties according to local conditions.
2. Use disease-free seeds or disinfect the seeds; collect seeds from disease-free plants. For seed disinfection, generally soak the seeds in 1% copper sulfate or 0.1% silver nitrate or 2% formalin solution for 10 minutes, then rinse the solution off thoroughly with clean water, and then sprout them or dry them for sowing. You can also dress the seeds with 15% triadimefon wettable powder at 0.2% of the seed weight.
3. Seedbed management: choose a non-continuous-cropping plot with high, dry terrain, good drainage and fertile soil for the seedbed, plant it far from tobacco stubble fields, vegetable gardens, curing barns and tobacco sheds, and use plastic film mulching for seedling raising. Plant at a reasonable density and pay attention to field ventilation; the seedbed land should be level, and before sowing carry out ”double soaking of the bottom” or ”triple soaking of the bottom”, avoid watering during the seedbed stage as much as possible, and choose a sunny morning to do it; avoid flood irrigation. Apply fully decomposed fertilizer and increase phosphorus and potassium fertilizer to improve the disease resistance of the plants.
4. Strengthen cultivation management. Be careful not to apply fertilizer carrying the pathogen. The bed surface of the tobacco field should be level, and drainage ditches should be made well to prevent water from accumulating in the beds after rain. The sowing density should be appropriate, not too dense; thin the seedlings early and set the seedlings sparsely, so as to promote strong seedling growth and improve disease resistance. After the tobacco seedlings emerge, it is advisable to irrigate frequently with a small amount of water and avoid flood irrigation.
Tobacco anthracnose is easily confused with weather fleck. The similarity between the two is that both produce small brown spots on tobacco plant leaves, so they must be carefully identified; only by treating the right disease will the treatment work.