The harmfulness of this fungus involves rapid spread among healthy plants. The incubation period is only 5-6 days. Infection with this disease prevents normal pollination of the plant and its further development.
The spread of the agent of this disease is most active in wet cloudy weather. Sharp temperature variations, poor illumination, high humidity create favorable conditions for fungus growth on the surface of cucumber leaves. At temperature above 20°C this process stops. Also spores of the fungus can be transmitted from weeds.
Powdery mildew is a fungal disease that can be identified externally on cucumber leaves in the form of spots of rusty or whitish color, while on stems and fruits such a plaque is much less common. This disease causes drying and early death of a cucumber. You can determine powdery mildew already on the real leaves of the cucumber, much less often - on the embryo. Initially, the fungus is located more on the top of the plant, then spreads to the entire shoot.
Infected plant is easily recognized by a noticeable in development gap in comparison with other plants. Initially, white spots are not noticeable, but from small rounded inclusions they quickly expand and cover the entire surface of the leaf. Then, the leaves of this plant are deformed and dry up. In the final stage a whitish coating covers the entire bush. The plant begins to gradually shed leaves and fade. In neglected cases, the whole plant dies.
In greenhouses, cucumbers that grow near the entrance first are affected by powdery dew, as well as in poorly sheltered places, where it is usually wetter and cooler. Besides, a possible cause of this disease is a lack of calcium in the soil or surfeit of nitrogen in it.
To prevent powdery mildew on the cucumber, clean the soil from weeds and any other plant residues before sowing. It is also important to isolate sowing from other crops. These measures help to prevent the transfer of mildew spores from neighboring plants or weeds.