What Pesticides Work Well to Control Tobacco Weather Fleck

Tobacco weather fleck is a physiological disease mainly caused by ozone, nitrogen compounds and other substances in the air, and is one of the major tobacco diseases worldwide. So what pesticide should be used for tobacco weather fleck?

1. What pesticide to use for tobacco weather fleck

Weather fleck is a physiological disease, and ordinary fungicides are ineffective against it, but some protective fungicides can be used in production. When scattered symptoms appear in the field, starting from the rosette stage, spray the leaves with monopotassium phosphate or Bordeaux mixture, or spray the leaves with a 500-fold dilution of zineb or a 700-fold dilution of thiophanate-methyl.

2. Causes of the disease

1. Variety: Large-scale outbreaks of tobacco weather fleck are related to the long-term planting of relatively susceptible varieties. The three varieties Yunyan 87, Yunyan 97 and K326 have weaker resistance, which is also an important reason for the occurrence and spread of tobacco weather fleck.

2. Flue-cured tobacco transplanting period: Long periods of low temperature and scant sunshine mean the seedlings cannot grow early and quickly after transplanting, resulting in uneven growth of tobacco seedlings, tender and weak tobacco plants, and poor stress resistance, making them prone to infection.

3. Rainfall: Large-scale rainfall hinders the root growth of tobacco plants and causes nutrient loss in tobacco fields, forming a microclimate environment in the tobacco field that favors major outbreaks of weather fleck.

4. Cold air: Cold air attacks can cause the incidence of weather fleck to reach about 40%, with affected area exceeding 200 hm2. In summary, during the susceptible stage, there are more rainy days, sunshine hours remain low, field humidity increases, and temperatures are suitable, fully meeting the meteorological conditions required for the occurrence and spread of weather fleck, thereby increasing the degree of disease occurrence and damage.

3. Control methods

1. Choose disease-resistant varieties: A number of disease-resistant or disease-tolerant varieties have been bred and introduced in China, and have been demonstrated and promoted at different stages and in different regions. Among them, varieties such as Yunyan 97, Honghua Dajinyuan, NC89 and Cuibi No. 1 have good disease resistance effects.

2. Do a good job in cultivation management: Since weather fleck mainly occurs on lower and middle leaves, effective cultivation management measures include the following aspects: First, remove 2 foot leaves and the lower 2 to 3 unusable tobacco leaves, to effectively improve the field microclimate, reduce soil moisture, and reduce the occurrence of the disease; second, carry out intertillage and hilling to keep the soil loose, promote tobacco root growth, and improve the stress resistance of tobacco plants; third, keep the field clean and free of weeds to improve air and light penetration between rows.

3. Water and fertilizer management: Follow the fertilization principle of controlling nitrogen fertilizer and increasing the application of phosphorus and potassium fertilizers, and apply fertilizer according to a formula to avoid excessive growth of tobacco plants. Keep the ratio of nitrogen, phosphorus and potassium balanced when fertilizing, and at the same time increase the application of organic fertilizer and farmyard manure to improve the soil properties of tobacco fields, thereby enhancing the resistance of tobacco plants.

Weather fleck is unavoidable. If it occurs, it will cause a relatively large impact, so it can only be prevented and controlled through daily management.