Late blight on onion leaves

Disease name: Late blight of onion leaves

The scientific name: Stemphylium vesicarium

Type of disease: fungal

Disease family: Pleosporaceae

(The appearance of the initial symptoms of late blight on onion leaves)

• The causes of disease:

Stemphylium leaf blight or late blight, where Stemphylium fungi infect onion leaves, which overwinter on plant remains and at the beginning of spring infect plants as a secondary infection with some diseases.

• Symptoms of the disease:

Brown, oval-shaped spots appear on the leaves and are soaked in water and darker during the spore formation stage. The infection can become severe and the disease can spread to the rest of the plant, where brown spots spread to the stems and fruits.

• Disease development cycle:

When temperatures rise in spring, ascospores are released into the air from the plant debris where the fungus lived, infecting nearby leaves that are usually infected with other diseases such as powdery mildew, insects, heat stress, or exposure to chemicals.

(Development of infection on onion leaves)

• Conditions suitable for the spread of the disease:

Mushrooms need moderate to warm temperatures and high humidity resulting from rainfall or irrigation, and this occurs in the spring, which is the growth season for these fungi.

• Losses resulting from the spread of the disease:

The fungus infects onion leaves, which die if the infection is neglected, leading to a decrease in the area for photosynthesis, as the fruits appear smaller and of lower quality.

(Onion leaf death due to late blight)

• Control:

1. 
2. Chemical control: Using a fungicide containing phenhexamide, and combating powdery mildew or any disease that appears on the plant quickly to limit the spread of the disease.
3. Organic control: Use neem oil in cases of insect infestation, remove the remains of infected plants and dispose of them away from the field.

• preventive measures:

1. Avoid planting onion crops for 3 years in the infected field.
2. Maintain good fertilization and avoid excessive use of nitrogen.
3. Maintain appropriate moisture levels in the crop.
4. Use herbicides properly to avoid plant poisoning.
5. Sterilize agricultural tools before use.

(The spread of late blight in onion crops)

• Sources:
• https://vegpath.plantpath.wisc.edu/diseases/onion-stemphylium-leaf-blight/