Early blight on onion leaves

Disease name: Early blight on onion leaves

The scientific name: Botrytis squamosa

Type of disease: fungal

Disease family: Sclerotiniaceae

(Initial symptoms appear on onion leaves as a result of early blight)

• The causes of disease:

Early blight or Botrytis leaf blight occurs mainly on onion leaves, where the fungus forms hardened structures on infected tissue that can persist in the soil for months to years.

• Symptoms of the disease:

The initial symptoms of the disease appear in the form of white, oval-shaped spots on onion leaves, with a watery back and a pale green halo forming around the spots. As the severity of the infection increases, the spots on the leaves increase, causing the tips of the leaves to die, and the entire leaves may eventually die.

(Development of early blight on onion leaves)

• Disease development cycle:

Mushroom spores are transmitted by the wind and infect onion leaves. In the presence of suitable weather conditions, the fungi germinate and produce enzymes that kill the leaf tissue, causing spots to appear on the leaves.

• Conditions suitable for the spread of the disease:

To infect leaves, the fungus requires temperatures ranging between 15-20 degrees Celsius, and humid conditions where leaf surfaces are wet from dew or rain for long periods of up to 20 hours or more for leaf spots to develop.

(Development of early blight symptoms)

• Losses resulting from the spread of the disease:

If the infection is neglected, the disease spreads in the field, causing onion leaves to appear wilted and yellowish in color, leading to significant losses in the quantity and quality of the crop.

• Control:

1. Organic control: Avoid overhead spraying and use drip irrigation. Plant residues and harmful weeds must be eliminated in the field and fertilization should be stopped when the first symptoms appear.
2. Chemical control: Fumigating the soil helps reduce the severity of the infection or using fungicides containing chlorthalonil or iprodione.

• preventive measures:

1. Leave enough space between each plant to enhance air circulation in the field.
2. Avoid planting onions in a field that has been infected for 3 years.
3. Use disease-free seedlings.
4. Use a good irrigation and drainage system to reduce soil moisture.

(The spread of early blight in onion crops)

• Sources:

– https://ipm.ucanr.edu/agriculture/onion-and-garlic/botrytis-leafspot/

– https://plantix.net/ar/library/plant-diseases/100212/botrytis-leaf-blight/