Tobacco
Blue Mould of Tobacco
Peronospora hyoscyami
Fungus
In a Nutshell
- Yellow spots on older leaves.
- Grey mould on underside of leaf.
Can also be found in
Tobacco
Symptoms
Single or groups of yellow spots appear on the older, shaded leaves. Additionally, dense gray mould can appear on the underside of the leaf lesions. The spots can spread and the leaves eventually die. Finally, the plant grows smaller than it should. Sometimes, the fungus can spread throughout the stem. This can cause the plant to stop growing and wilt at any age. Brown streaks can be found inside these stems. A sign in the nursery for the disease being present are patches of dead or dying seedlings. At first, the top of the leaves may look normal, but after a day or two, yellow spots develop. Seedlings will start to die and turn light brown.
Recommendations
Organic Control
Currently, there are no biological products available to control blue mould disease.
Chemical Control
Most of the time the control of blue mould chemically is necessary in temperate and subtropical tobacco areas. Dithiocarbamates or systemic products with residual activity are used. Use pesticides regulated for your area. Always follow the label for the correct application. Inform yourself on the resistance of the pathogen to the pesticide of your choice. Chemical sprays are not effective against systemic infection.
What caused it?
The damage is created by a plant pathogen called Peronospora hyoscyami which causes Blue Mould. It is a fungal disease that affects tobacco plants. It is spread through wind-blown spores and infected transplants. Once it is present, it grows by infecting the plant tissue. Under optimal conditions, the fungus produces the next generation of spores within 7-10 days after initial infection. The fungus requires cool, wet, and cloudy weather to produce spores, and disease epidemics may become severe under these conditions. When the climate is sunny, hot, and dry, the fungus survives poorly.
Preventive Measures
- Prevention measures are essential to avoid the infestation of blue mould in tobacco plants.
- The pathogen is highly dependent on a cool, humid environment to reproduce and infect the tobacco plant.
- Keep the growing area as thoroughly drained.
- Avoid overhead irrigation as it favours disease development.
- Drip irrigation is a better option as it reduces the level of blue Mould in comparison with overhead irrigation.
- Maintain appropriate plant spacing and limit nitrogen fertilisation that can cause excess growth.
- Search for resistant cultivars.
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