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Signs of damage
- At the beginning of the development of peronosporosis, the spots are small, pointy, single, or numerous;
- As the disease progresses, they increase in size, acquire a brown color, and can even cover the entire surface;
- Pale yellow, blurred yellow spots are formed on the upper side of the cotyledons and leaves of the affected plants;
- At a high relative humidity of the air on the underside of the leaves, a light-gray loose coating from the conidial sporulation of the fungus is formed in the affected areas;
- On adult plants, the disease usually manifests itself on the lower leaves;
- Severely affected plants rot and die within a few days.
How to prevent
Prevention of the spread of the fungus, although one cannot prevent the development of downy mildew completely, is definitely able to minimize the likely development. All you need is to regularly inspect the plantations (studying the leaves on both sides), maintain temperature and microclimate control in the greenhouse, conduct air drying, and timely feed with organic and mineral fertilizers. It is also possible to do preventive seed treatment before planting.
Healing and protection measures may include but are not limited to such methods as collecting seeds only from healthy plants, culling of seedlings, collecting plant residues in autumn, treating seeds before sowing with drugs, hydrothermal treatment of seeds in hot water of around 22 °F (50 °C) for 20 minutes with further cooling in cold water for 2-3 minutes as well as the treatment of seedlings with a fungicide when signs of downy mildew appear. You should treat the cut site with crushed charcoal when you get rid of the damaged parts. Also, stop or minimize the watering during the treatment period, as lowering the humidity level is an important factor.
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