What are the latest control methods for tobacco brown spot disease?
Tobacco brown spot disease is a disease caused by fungi. Tobacco farmers in China commonly call it red spot, root tiger eye, fire blister spot, etc. It is the main leaf spot disease during the tobacco leaf maturity period and occurs in all tobacco-growing areas in China. It not only makes tobacco leaves incomplete and lowers their grade, but also, due to uncoordinated internal quality, worsens the taste and reduces industrial use value. Now let us take a look at how to control tobacco brown spot disease!
Symptoms of tobacco brown spot disease
In the middle and late stages in the field, disease spots begin to appear on the lower leaves of the tobacco plant. At first they are small yellowish-brown round spots, later expanding to 1-2 cm. The spots are round or irregularly round, with a yellow halo around them, and obvious concentric rings centered on the middle of the spot appear on them. They are brittle and easily broken. When the air is humid, dark brown or blackish-brown mold-like substances are produced on the spots, namely the pathogen's conidiophores and conidia (the basis for field diagnosis). When the weather is dry, the centers of the spots often crack and are prone to perforation. In severe cases, the spots can merge with one another to form large spots and crack and fall off. When the main veins, flower stalks, capsules and stems are infected by the pathogen, smaller dark brown or black spots can be produced. Near harvest time, round or nearly round dark brown sunken spots appear on the stems.
Occurrence pattern of tobacco brown spot disease
The fungus overwinters as mycelium on diseased residues. When conditions are suitable the following year, it produces conidia, which spread by wind and rain. In tobacco fields where susceptible varieties are planted on a large scale, where rain is concentrated during the maturity period (July-August), where nitrogen application is excessive, where planting density is high and where ventilation and light penetration in the field are poor, epidemics are likely to occur.
Agricultural control of tobacco brown spot disease
1. Select resistant (tolerant) varieties: Resistant varieties include Zhongyan 98, etc. Moderately resistant varieties include Yunyan 85, K326, RG11, G28, K346, etc. RG17 and Zhongyan 9203 also have a certain degree of disease resistance.
2. Increase application of organic fertilizer: Appropriately increase the application of organic fertilizer and cake fertilizer, control the amount of nitrogen fertilizer, strengthen field management, and improve the disease resistance of tobacco plants.
3. Reasonable close planting: Especially in severely affected areas, it is required that rows do not close at the mature plant stage, and that contiguous areas be moderate rather than too large, so as to avoid the disease being difficult to control once it becomes epidemic.
4. Topping and harvesting at the right time: Determine the topping time according to soil fertility and variety. If topping is too early, the upper leaves grow too large, the tobacco plant often becomes umbrella-shaped, and ventilation and light penetration for the lower leaves are poor, making them vulnerable to the pathogen. Harvesting mature tobacco leaves at the right time can prevent and control the occurrence and spread of the disease and reduce damage.
5. Reasonable crop rotation: Implement a crop rotation system of more than 2 years.
Chemical control of tobacco brown spot disease
1. At the first harvest of the bottom leaves, spray with 40% dimethachlon wettable powder at 400-500 times dilution, using 50-75 kg of solution per mu, once every 10 days, for 2-3 consecutive times. The control effect is relatively good.
2. At the budding stage of the tobacco plant, spray the leaves with 1.5% polyoxin at 100 times dilution or 0.3% kasugamycin at 200 times dilution, using 50-75 kg of solution per mu, and apply once more half a month later. The control effect is relatively good.
3. In the early stage of disease occurrence, use 10% polyoxin wettable powder at 800-1000 times dilution, once every 7-10 days, for 2-3 consecutive times. Or use 30% dimethachlon suspension concentrate at 600-800 times dilution, or 47% dimethachlon wettable powder at 600-900 times dilution for spray control, using 50-75 kg per mu, once every 7-10 days, for a total of 2-3 sprays. The control effect is relatively good.
4. In tobacco fields where brown spot disease and wildfire disease occur together, use 45% Jinyeshu wettable powder at 500-600 times dilution for spray control, once every 7-10 days, for a total of 2 sprays. The control effect is relatively good.