How to prevent and control tobacco brown spot? What other diseases are there?

Tobacco is widely cultivated in all provinces and regions of northern and southern China. Besides being made into tobacco products for people to smoke, it can also be used for medical treatment and for eliminating the “four pests” (snails, mosquitoes, flies, mice) and for killing insects. So, how do you prevent and control tobacco brown spot? What other diseases are there?

1. How do you prevent and control tobacco brown spot?

1. Which parts are mainly affected?

Brown spot is one of the main tobacco diseases. It mainly affects the leaves, stems, flower stalks, and capsules. It occurs severely in Shandong, Henan, Anhui, Heilongjiang, Jilin, and other places, followed by the tobacco-growing areas of Sichuan, Yunnan, Guizhou, Liaoning, Shaanxi, and others.

2. When does the disease occur?

When the temperature reaches 7-8°C in the spring of the following year and the relative humidity is greater than 50%, the brown spot pathogen begins to produce conidia, which are spread by airflow, wind, and rain to tobacco plants in the field and infect the lower leaves (primary infection); conidia are then produced again on the lesions of these diseased tobacco plants and spread by wind and rain, causing secondary infection; after repeated secondary infections, the pathogen can infect any part such as flower stalks, capsules, side branches, and stems.

3. What are the symptoms of the disease?

Leaf infection mostly starts from the lower leaves and gradually develops upward. At first, there are small yellowish-brown spots, which later develop into brown round or nearly round spots. The lesions are brittle and easily broken, and in severe cases the leaves become fragmented; when veins, flower stalks, capsules, and stems are infected, long oval or spindle-shaped dark brown sunken spots appear.

4. What are the prevention and control methods?

(1) Agricultural prevention: First, plant tobacco varieties with relatively strong resistance to brown spot; second, apply more organic fertilizer to improve the disease resistance of tobacco plants; third, do not plant too densely, so as to avoid rapid spread after the disease occurs; fourth, maintain field sanitation, and the removed bottom leaves, tobacco suckers, and tobacco stalks should be taken out of the field and deeply buried or dried and destroyed; fifth, implement a crop rotation system of more than 2 years.

(2) Chemical prevention: At the first harvest of bottom leaves, spray with 40% dimethachlon wettable powder at 400-500 times dilution, once every 10 days, for 2-3 consecutive times; at the budding stage, spray the leaves with 1.5% polyoxin at 100 times dilution, and apply once more half a month later.

(3) Chemical treatment: In the early stage of the disease, spray with 10% polyoxin wettable powder at 800-1000 times dilution, once every 7-10 days, for 2-3 consecutive times, or spray with 30% dakeli suspension concentrate at 600-800 times dilution or 47% baofengning wettable powder at 600-900 times dilution, once every 7-10 days, for a total of 2-3 sprays.

2. What other tobacco diseases are there?

Other tobacco diseases include mosaic disease, bacterial wilt, black shank, anthracnose, powdery mildew, wildfire disease, angular leaf spot, sooty mold, damping-off, downy mildew, sclerotinia rot, southern blight, black spot, frog-eye leaf spot, and others. Only a few are introduced here.

1. Mosaic disease: It is mainly transmitted through contact, but aphids can also transmit some varieties. Failure to pay attention to sanitary operations is the key to causing a mosaic disease epidemic. At present, there is no single treatment method for mosaic disease, so prevention is the main approach; carry out reasonable crop rotation, maintain field sanitation, emphasize sanitary operations, control aphids, and apply agents such as virus-clearing, toxin-eliminating, and fungus-virus-clearing preparations before the virus enters for prevention.

2. Bacterial wilt: The main sources of primary infection are pathogenic bacteria in soil, diseased residues, and fertilizer, and flowing water in diseased fields is the most important way of secondary infection and spread of the disease; you can select disease-resistant varieties, do a good job in disinfection, use crop rotation of more than 3 years, use high ridges and irrigation and drainage, do not use diseased plants to make compost, and after timely removal of diseased plants, disinfect the diseased holes with quicklime.

3. Black shank: Soil is the most important source of infection, followed by compost made from diseased plant residues, and the most important transmission medium is surface flowing water; you can select disease-resistant varieties, use crop rotation of more than 3 years, use high ridges and irrigation and drainage, and when scattered disease occurs, spray the leaf surface with Gaoke 30% metalaxyl-hymexazol at 600 times dilution, and diseased stems and leaves should be promptly removed and burned or deeply buried.

4. Angular leaf spot: The pathogen overwinters in diseased residues or seeds, and can also survive near the root systems of some crops and weeds, becoming the source of primary infection of the disease the following year. The pathogen is mainly spread by wind, rain, and insects; seeds should be disinfected, and seedbeds should also be disinfected, with timely ventilation and dehumidification, weeding and thinning, drainage to release moisture, crop rotation for 2-3 years, and after the disease occurs, remove diseased leaves or diseased plants and spray 200 units of agricultural streptomycin.

5. Southern blight: The pathogen overwinters in the soil as sclerotia or mycelial masses and is often spread with soil, organic fertilizer, and irrigation water; use crop rotation of more than 3 years, apply compost fermented with enzyme bacteria or fully decomposed bio-organic fertilizer, apply plant ash as a topdressing in the middle and late growth stages, and in the early stage of the disease use 50% carbendazim wettable powder at 1000 times dilution, focusing the spray on the stem base, once every 7-10 days, for 2-3 consecutive treatments.

The above is an introduction to the prevention and control methods for tobacco brown spot and other diseases. I hope it is useful to everyone.