Blue mould

Causal Agent: Peronospora hyoscyami f. sp. tabacina is a fungus that causes blue mold disease, a devastating downy mildew affecting tobacco (Nicotiana tabacum).

Symptoms:

Leaf Lesions:
- The fungus primarily affects the leaves, causing the development of pale green to yellow lesions on the upper leaf surface.
Underside Growth:
- White to grayish downy growth (sporulation) on the undersides of infected leaves, particularly during humid conditions.
Necrosis:
- Lesions can enlarge, leading to necrosis and tissue death.
Reduced Photosynthesis:
- Severe infections can result in reduced photosynthetic activity and stunted growth.

Identification:

Downy Growth:
- Presence of characteristic downy growth on the undersides of leaves.
Lesion Appearance:
- Pale green to yellow lesions on the upper leaf surface.

Conditions Favoring Disease:

High Humidity:
- Optimal Growth Conditions: Downy mildews, including Peronospora hyoscyami f. sp. tabacina, thrive in high humidity.
Moderate Temperatures:
- Moderate temperatures, typically ranging from 15 to 24 degrees Celsius (59 to 75 degrees Fahrenheit), favor disease development.

Management:

Fungicides:
- Application of fungicides, especially those effective against downy mildews, can be part of an integrated disease management strategy.
Cultural Practices:
- Proper spacing of tobacco plants and pruning to enhance air circulation can help reduce humidity and minimize disease spread.
Resistant Varieties:
- Planting tobacco varieties that exhibit resistance or tolerance to blue mold.
Avoiding Overhead Irrigation:
- Minimizing water on foliage, especially through the use of drip irrigation, can reduce the risk of downy mildew.

Note: Blue mold caused by Peronospora hyoscyami f. sp. tabacina is a significant concern in tobacco cultivation due to its potential to cause yield losses. Early detection, regular monitoring, and the implementation of control measures are crucial for managing this downy mildew disease.